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Sound in Aristotle

An echo occurs, when, a mass of air having been unified,
bounded, and prevented from dissipation by the containing
walls of a vessel, the air originally struck by the impinging body
and set in movement by it rebounds from this mass of air like a
ball from a wall. It is probable that in all generation of sound
echo takes place, though it is frequently only indistinctly heard.
What happens here must be analogous to what happens in the
case of light; light is always reflected – otherwise it would not
be diffused and outside what was directly illuminated by the
sun there would be blank darkness; but this reflected light is
not always strong enough, as it is when it is reflected from
water, bronze, and other smooth bodies, to cast a shadow, which
is the distinguishing mark by which we recognize light.


What has the power of producing sound is what has the power
of setting in movement a single mass of air which is continuous
from the impinging body up to the organ of hearing. The organ
of hearing is physically united with air, and because it is in air,
the air inside is moved concurrently with the air outside. Hence
animals do not hear with all parts of their bodies, nor do all
parts admit of the entrance of air; for even the part which can
be moved and can sound has not air everywhere in it. Air in
itself is, owing to its friability, quite soundless; only when its
dissipation is prevented is its movement sound. The air in the
ear is built into a chamber just to prevent this dissipating
movement, in order that the animal may accurately apprehend
all varieties of the movements of the air outside. That is why we
hear also in water, viz. because the water cannot get into the air
chamber or even, owing to the spirals, into the outer ear. If this
does happen, hearing ceases, as it also does if the tympanic
membrane is damaged, just as sight ceases if the membrane
covering the pupil is damaged. It is also a test of deafness
whether the ear does or does not reverberate like a horn; the air
inside the ear has always a movement of its own, but the sound
we hear is always the sounding of something else, not of the
organ itself. That is why we say that we hear with what is
empty and echoes, viz. because what we hear with is a chamber
which contains a bounded mass of air.


In some cases there is no discrepancy of any sort in the names
used, but a difference of kind between the meanings is at once
obvious: e.g. in the case of ‘clear’ and ‘obscure’: for sound is
called ‘clear’ and ‘obscure’, just as ‘colour’ is too. As regards the
names, then, there is no discrepancy, but the difference in kind
between the meanings is at once obvious: for colour is not
called ‘clear’ in a like sense to sound.

Further, see in regard
to their intermediates, if some meanings and their contraries
have an intermediate, others have none, or if both have one but
not the same one, e.g. ‘clear’ and ‘obscure’ in the case of colours
have ‘grey’ as an intermediate, whereas in the case of sound
they have none, or, if they have, it is ‘harsh’, as some people say
that a harsh sound is intermediate. ‘Clear’, then, is an
ambiguous term, and likewise also ‘obscure’. See, moreover, if
some of them have more than one intermediate, while others
have but one, as is the case with ‘clear’ and ‘obscure’, for in the
case of colours there are numbers of intermediates, whereas in
regard to sound there is but one, viz. ‘harsh’.


The void is thought to be place with nothing in it. The reason
for this is that people take what exists to be body, and hold that
while every body is in place, void is place in which there is no
body, so that where there is no body, there must be void.
Every body, again, they suppose to be tangible; and of this
nature is whatever has weight or lightness.
Hence, by a syllogism, what has nothing heavy or light in it, is
This result, then, as I have said, is reached by syllogism. It
would be absurd to suppose that the point is void; for the void
must be place which has in it an interval in tangible body.
But at all events we observe then that in one way the void is
described as what is not full of body perceptible to touch; and
what has heaviness and lightness is perceptible to touch. So we
would raise the question: what would they say of an interval
that has colour or sound – is it void or not? Clearly they would
reply that if it could receive what is tangible it was void, and if
not, not.


From all this it is clear that the theory that the movement of the stars
produces a harmony, i.e. that the sounds they make are concordant,
in spite of the grace and originality with which it has been stated, is
nevertheless untrue. Some thinkers suppose that the motion of
bodies of that size must produce a noise, since on our earth the
motion of bodies far inferior in size and in speed of movement has
that effect. Also, when the sun and the moon, they say, and all the
stars, so great in number and in size, are moving with so rapid a
motion, how should they not produce a sound immensely great?
Starting from this argument and from the observation that their
speeds, as measured by their distances, are in the same ratios as
musical concordances, they assert that the sound given forth by the
circular movement of the stars is a harmony. Since, however, it
appears unaccountable that we should not hear this music, they
explain this by saying that the sound is in our ears from the very
moment of birth and is thus indistinguishable from its contrary


There is not only the absurdity of our hearing nothing, the ground of
which they try to remove, but also the fact that no effect other than
sensitive is produced upon us. Excessive noises, we know, shatter the
solid bodies even of inanimate things: the noise of thunder, for
instance, splits rocks and the strongest of bodies. But if the moving
bodies are so great, and the sound which penetrates to us is
proportionate to their size, that sound must needs reach us in an
intensity many times that of thunder, and the force of its action must
be immense. Indeed the reason why we do not hear, and show in our
bodies none of the effects of violent force, is easily given: it is that
there is no noise. But not only is the explanation evident; it is also a
corroboration of the truth of the views we have advanced. For the
very difficulty which made the Pythagoreans say that the motion of
the stars produces a concord corroborates our view.

Indeed, this must be recognized as the cause of the fire that is
generated in the earth: the air is first broken up in small
particles and then the wind is beaten about and so catches fire.
A phenomenon in these islands affords further evidence of the
fact that winds move below the surface of the earth. When a
south wind is going to blow there is a premonitory indication: a
sound is heard in the places from which the eruptions issue.
This is because the sea is being pushed on from a distance and
its advance thrusts back into the earth the wind that was
issuing from it. The reason why there is a noise and no
earthquake is that the underground spaces are so extensive in
proportion to the quantity of the air that is being driven on that
the wind slips away into the void beyond.

Subterranean noises, too, are due to the wind; sometimes they
portend earthquakes but sometimes they have been heard
without any earthquake following. Just as the air gives off
various sounds when it is struck, so it does when it strikes other
things; for striking involves being struck and so the two cases
are the same. The sound precedes the shock because sound is thinner and passes through things more readily than wind. But
when the wind is too weak by reason of thinness to cause an
earthquake the absence of a shock is due to its filtering through
readily, though by striking hard and hollow masses of different
shapes it makes various noises, so that the earth sometimes
seems to ‘bellow’ as the portentmongers say


But if any of the dry exhalation is caught in the process as the
air cools, it is squeezed out as the clouds contract, and collides
in its rapid course with the neighbouring clouds, and the sound
of this collision is what we call thunder. This collision is
analogous, to compare small with great, to the sound we hear in
a flame which men call the laughter or the threat of Hephaestus
or of Hestia. This occurs when the wood dries and cracks and
the exhalation rushes on the flame in a body. So in the clouds,
the exhalation is projected and its impact on dense clouds
causes thunder: the variety of the sound is due to the

What is capable of taking on colour is what in itself is
colourless, as what can take on sound is what is soundless;
what is colourless includes (a) what is transparent and (b) what
is invisible or scarcely visible, i.e. what is ‘dark’. The latter (b) is
the same as what is transparent, when it is potentially, not of
course when it is actually transparent; it is the same substance
which is now darkness, now light.

Sound may mean either of two things (a) actual, and (b)
potential, sound. There are certain things which, as we say,
‘have no sound’, e.g. sponges or wool, others which have, e.g.
bronze and in general all things which are smooth and solid –
the latter are said to have a sound because they can make a
sound, i.e. can generate actual sound between themselves and
the organ of hearing.
Actual sound requires for its occurrence (i, ii) two such bodies
and (iii) a space between them; for it is generated by an impact.
Hence it is impossible for one body only to generate a sound –
there must be a body impinging and a body impinged upon;
what sounds does so by striking against something else, and
this is impossible without a movement from place to place.

Actual sound requires for its occurrence (i, ii) two such bodies
and (iii) a space between them; for it is generated by an impact.
Hence it is impossible for one body only to generate a sound –
there must be a body impinging and a body impinged upon;
what sounds does so by striking against something else, and
this is impossible without a movement from place to place.

As we have said, not all bodies can by impact on one another
produce sound; impact on wool makes no sound, while the
impact on bronze or any body which is smooth and hollow
does. Bronze gives out a sound when struck because it is
smooth; bodies which are hollow owing to reflection repeat the
original impact over and over again, the body originally set in
movement being unable to escape from the concavity.
Further, we must remark that sound is heard both in air and in
water, though less distinctly in the latter. Yet neither air nor
water is the principal cause of sound. What is required for the
production of sound is an impact of two solids against one
another and against the air. The latter condition is satisfied
when the air impinged upon does not retreat before the blow,
i.e. is not dissipated by it.
That is why it must be struck with a sudden sharp blow, if it is
to sound – the movement of the whip must outrun the
dispersion of the air, just as one might get in a stroke at a heap
or whirl of sand as it was traveling rapidly past


The distinctions between different sounding bodies show
themselves only in actual sound; as without the help of light
colours remain invisible, so without the help of actual sound
the distinctions between acute and grave sounds remain
inaudible. Acute and grave are here metaphors, transferred from
their proper sphere, viz. that of touch, where they mean
respectively (a) what moves the sense much in a short time, (b)
what moves the sense little in a long time. Not that what is
sharp really moves fast, and what is grave, slowly, but that the
difference in the qualities of the one and the other movement is
due to their respective speeds. There seems to be a sort of
parallelism between what is acute or grave to hearing and what
is sharp or blunt to touch; what is sharp as it were stabs, while
what is blunt pushes, the one producing its effect in a short, the
other in a long time, so that the one is quick, the other slow.


Voice then is the impact of the inbreathed air against the
‘windpipe’, and the agent that produces the impact is the soul
resident in these parts of the body. Not every sound, as we said,
made by an animal is voice (even with the tongue we may
merely make a sound which is not voice, or without the tongue
as in coughing); what produces the impact must have soul in it
and must be accompanied by an act of imagination, for voice is
a sound with a meaning, and is not merely the result of any

Sound in Diodorus Siculus

They also recount that he carried along with his… a great number of women, and that when he joined battle in his wars he used the sounds of
drums and cymbals, since the trumpet had not yet been discovered.

double for a certain distance, but they divide the
inner portions still further, wdth the result that it
becomes a double tongue as far as its base. Consequently
they are very versatile as to the sounds they
can utter, since they imitate not only every articulate
language used by man but also the varied chatterings
of the birds, and, in general, they can reproduce
any peculiarity of sound.


There are also in the island, they say,
abundant springs of water, the warm springs serving
well for bathing and the relief of fatigue, the cold
excelling in sweetness and possessing the power to
contribute to good health. Moreover, the inhabitants
give attention to every branch of learning
and especially to astrology ; and they use letters
which, according to the value of the sounds they
represent, are twenty-eight in number, but the
characters are only seven, each one of which can be
formed in four different ways.


Consequently it comes to pass that when
the Ethiopians come out of the marshy lands they
are eaten by these beasts ; for they are unable to
\vithstand the might of the lions, since they have no
help in the form of weapons, and indeed in the end
the race of them would have been utterly destroyed
had not Nature provided them with an aid which
acts entirely of itself. For at the time of the rising
of the dog-star,^ whenever a calm unexpectedly
comes on, there swarms to these regions such a
multitude of mosquitoes, surpassing in vigour those
that are knowTi to us, that while the human beings
find refuge in the marshy pools and suffer no hurt,
all the lions flee from those regions, since they not
only suffer from their stings but are at the same time
terrified by the sound of their humming.


The animals which bear the name cynocephali ‘ are
in body like misshapen men, and they make a sound
like the whimpering of human beings. These
animals are very wild and quite untamable, and
their eyebrows give them a rather surly expression.
A most peculiar characteristic of the female is that it
carries the womb on the outside of its body during
its entire existence.


three islands which lie off the coast
just described and provide numerous harbours. The
first of these, history relates, is sacred to Isis and is
uninhabited, and on it are stone foundations of ancient
dwellings and stelae which are inscribed with letters
in a barbarian tongue ; the other two islands are likewise
uninhabited and all three are covered thick with
olive trees which differ from those we have. Beyond
these islands there extends for about a thousand
stades a coast which is precipitous and difficult for
ships to sail past ; for there is neither harbour
beneath the cliffs nor roadstead where sailors may
anchor, and no natural breakwater which affords
shelter in emergency for mariners in distress. And
parallel to the coast here runs a mountain range at
whose summit are rocks which are sheer and of a
terrifying height, and at its base are sharp undersea
ledges in many places and behind them are ravines
which are eaten away underneath and turn this way.

And since these ravines are connected
by passages with one another and the sea is deep, the
surf, as it at one time rushes in and at another time
retreats, gives forth a sound resembhng a mighty
crash of thunder. At one place the surf, as it breaks
upon huge rocks, leaps on high and causes an astonishing
mass of foam, at another it is swallowed up wdthin
the caverns and creates such a terrifying agitation of
the waters that men who unwittingly draw near
these places are so frightened that they die, as it
were, a first death.

The man who associated ^v^th her and loved her
more than anyone else, they say, was Marsyas the
Phrygian, who was admired for his intelligence and
chastity ; and a proof of his intelligence they find in
the fact that he imitated the sounds made by the
pipe of many reeds and carried all its notes over into
the flute,^ and as an indication of his chastity they
cite his abstinence from sexual pleasures until the
day of his death.

the hearers decided that Apollo presented the more
just argument, their skills were again compared;
Marsyas was defeated, and Apollo, who had become
somewhat embittered by the quarrel, flayed the
defeated man alive. But quickly repenting and being
distressed at what he had done, he broke the strings of
the lyre and destroyed the harmony of sounds which
he had discovered. This harmony of the strings , however,
was rediscovered, when the Muses added later
the middle string, Linus the string struck with the
forefinger, and Orpheus and Thamyras the lowest


This city lies on a certain island
which is surrounded by the river Triton and is precipitous
on all sides save at one place where there is
a narrow pass which bears the name ” Nysaean
Gates.” The land of the island is rich, is ti-aversed
at intervals by pleasant meadows and watered by
abundant streams from springs, and possesses every
kind of fruit-bearing tree and the wild vine in
abundance, which for the most part grows up trees.
The whole region, moreover, has a fresh and pure
air and is furthermore exceedingly healthful ; and
for this reason its inhabitants are the longest lived
of any in those parts. The entrance into the island
is like a glen at its beginning, being thickly shaded
by lofty trees growing close together, so that the
sun never shines at all through the close-set branches
but only the radiance of its light may be seen.
69. Everywhere along the lanes, the account con-

tinues, springs of water gush forth of exceeding
sweetness, making the place most pleasant to those
who desire to tarry there. Further in there is a
cave, circular in shape and of marvellous size and
beauty. For above and all about it rises a crag of
immense height, formed of rocks of different coloui’s ;
for the rocks lie in bands and send forth a bright
gleam, some like that purple which comes from the
sea,^ some bluish and others like every other kind of
brilliant hue, the result being that there is not a
colour to be seen among men which is not visible in
that place. Before the entrance grow marvellous
trees, some fruit-bearing, others evergreen, and all of
them fashioned by nature for no other end than to
delight the eye ; and in them nest every kind of
bird of pleasing colour and most charming song.
Consequently the whole place is meet for a god, not
merely in its aspect but in its sound as well, since
the sweet tones which nature teaches are always
superior to the song which is devised by art. When
one has passed the entrance the cave is seen to widen
out and to be lighted all about by the rays of the
sun, and all kinds of flowering plants grow there,
especially the cassia and every other kind which has
the power to preserve its fragrance throughout the
year ; and in it are also to be seen several couches
of nymphs, formed of every manner of flower, made
not by hand but by the hght touch of Nature herself,
in manner meet for a god. Moreover, throughout
the whole place round about not a flower or leaf is
to be seen which has fallen. Consequently those
who gaze upon this spot find not only its aspect
delightful but also its fragrance most pleasant.

Apollo played upon the lyre without
accompanying it with his voice, while Mai-syas,
striking up upon his pipes, amazed the ears of his
hearers by their strange music and in their opinion
far excelled, by reason of his melody, the first

Cleio is so named because the pi-aise
which poets sing in their encomia bestows great
glory (kleos) upon those who are praised ; Euterpe,
because she gives to those who hear her sing delight
(terpein) in the blessings which education bestows
Thaleia, because men whose praises have been sung
in poems flourish (thallein) through long periods of
time ; Melpomene, from the chanting (inelodid) by
which she charms the souls of her listeners ; Terpsichore,
because she delights (terpein) her disciples
with the good things which come from education

Sound in Sophocles

Good bye, my chambered home that kept me safe, and neighbouring Nymphs of field and stream, good bye, deep sounding roar of sea swept cape – 1455 here often indeed my head was battered, soaked and wet within my home by spume and flying foam, and often too the mount, Hermaeon, returned antiphonal my cries of echoing agony and pain, tempestuous grief. 1460 Now, though, you springs and water source Apolline, I am leaving, leaving you behind,

Keep silence, son.
Ne. What is it?
Ch. I hear a noise
str. as of a man who shares his life with caustic pain – somewhere over there, or there. It strikes, yes, strikes my ear the sound 205 authentic of a man who creeps in inevitable pain upon his way, nor can I fail to know the grievous sound far off of bitter human torment. Its tone is obvious.


This man is not far off, but close at hand, 211 no piping melody is his as of a shepherd in wild fields, but he cries out loud far off and stumbles in his dire necessity, 215 or when he sees the harbour innocent of ships, and his cry is loud and terrible to hear.


It is a miracle, I think, how he this man, how he, deserted and sole witness to the surge and chop of the surrounding, sounding sea held on so long to this life of tears.


This man second to none it may be
ant. of the houses hallowed by time, 181 has no share in life’s joys, lies abandoned, apart from mankind, his company the wild and dappled beasts, piteous both in his cries and his famine, 185 he gives tongue to the torment he feels, insupportable pains, with Echo, babbling, heard from afar, the only one to heed his bitter grief.

Sound in Plutarch

Agamemnon,a for example,
used nine heralds and, even so, had difficulty in
keeping the assembly in order because of the vast
numbers ; but here in Delphi, a few days hence, in
the theatre you will see that one voice reaches all.
In the same way, in those days, prophecy employed
more voices to speak to more people, but to-day,
quite the reverse, we should needs be surprised at the
god if he allowed his prophecies to run to waste, like
water, or to echo like the rocks with the voices of
shepherds and flocks in waste places.”


As a matter of fact, these statements of Phylarchus
are absurd, but even more absurd are those put forth
by those who say that Serapis is no god at all, but
the name of the coffin of Apis ; and that there are
in Memphis certain bronze gates called the Gates of
Oblivion and Lamentation, which are opened when
the burial of Apis takes place, and they give out a
deep and harsh sound ; and it is because of this that
we lay hand upon anything of bronze that gives out
a sound.

For the same reason many of the Greeks
make statues of Dionysus in the form of a bull and
the women of Elis invoke him, praying that the god
may come with the hoof of a bull d
; and the epithet applied to Dionysus among the Argives is ” Son of the
Bull.” They call him up out of the water by the sound
of trumpets, at the same time casting into the depths
a lamb as an offering to the Keeper of the Gate. The
trumpets they conceal in Bacchic wands, as Socrates f
lias stated in his treatise on The Holy Ones.


And it is evident that Sophocles a assigns each of the
instruments to each god in these words :
No harp, no lyre is welcome for laments.
” As a matter of fact it was only after a long lapse of
time and only recently that the flute ventured to utter
a sound ‘ over things of delight/ but during all the early
time it used to be fetched in for times of mourning,
and it had the task of rendering service on these
occasions, not a very honourable or cheerful one.

libations poured over the victims and the refusal to
give responses unless the whole victim from the hoofjoints
up is seized with a trembling and quivering, as
the libation is poured over it ? Shaking the head is
not enough, as in other sacrifices, but the tossing and
quivering must extend to all parts of the animal alike
accompanied by a tremulous sound ; and unless this
takes place they say that the oracle is not functioning,
and do not even bring in the prophetic priestess.

Examples of Hearing in Tacitus’ Annals

It was a restless night for different reasons, the barbarians in their festivity filling the valleys under the hills and the echoing glens with merry song or savage shouts,

The barbarians meanwhile rushed down with their bands, now hurling at the entrenchments stones such as the hand could grasp, stakes with points hardened by fire, and boughs lopped from oaks; now filling up the fosses with bushes and hurdles and dead bodies, while others advanced up to the breastwork with bridges and ladders which they had constructed for the occasion, seized it, tore it down, and came to close quarters with the defenders. Our soldiers on the other side drove them back with missiles, repelled them with their shields, and covered them with a storm of long siege-javelins and heaps of stones. Success already gained and the more marked disgrace which would follow repulse, were a stimulus to the Romans, while the courage of the foe was heightened by this last chance of deliverance and the presence of many mothers and wives with mournful cries. Darkness, which increased the daring of some and the terror of others, random blows, wounds not foreseen, failure to recognise friend or enemy, echoes, seemingly in their rear, from the winding mountain valleys, spread such confusion that the Romans abandoned some of their lines in the belief that they had been stormed. Only however a very few of the enemy had broken through them; the rest, after their bravest men had been beaten back or wounded, were towards daybreak pushed back to the upper part of the fortress and there at last compelled to surrender. Then the immediate neighbourhood, by the voluntary action of the inhabitants, submitted. The early and severe winter of Mount Haemus saved the rest of the population from being reduced by assault or blockade.

There was as much restlessness in the German host with its hopes, its eager longings, and the conflicting opinions of its chiefs. Arminius advised that they should allow the Romans to quit their position, and, when they had quitted it, again surprise them in swampy and intricate ground. Inguiomerus, with fiercer counsels, heartily welcome to barbarians, was for beleaguering the entrenchment in armed array, as to storm them would, he said, be easy, and there would be more prisoners and the booty unspoilt. So at daybreak they trampled in the fosses, flung hurdles into them, seized the upper part of the breastwork, where the troops were thinly distributed and seemingly paralysed by fear. When they were fairly within the fortifications, the signal was given to the cohorts, and the horns and trumpets sounded. Instantly, with a shout and sudden rush, our men threw themselves on the German rear, with taunts, that here were no woods or swamps, but that they were on equal ground, with equal chances. The sound of trumpets, the gleam of arms, which were so unexpected, burst with all the greater effect on the enemy, thinking only, as they were, of the easy destruction of a few half-armed men, and they were struck down, as unprepared for a reverse as they had been elated by success. Arminius and Inguiomerus fled from the battle, the first unhurt, the other severely wounded. Their followers were slaughtered, as long as our fury and the light of day lasted. It was not till night that the legions returned, and though more wounds and the same want of provisions distressed them, yet they found strength, healing, sustenance, everything indeed, in their victory.

But Germanicus also bestowed attention on other wonders. Chief of these were the stone image of Memnon, which, when struck by the sun’s rays, gives out the sound of a human voice; the pyramids, rising up like mountains amid almost impassable wastes of shifting sand, raised by the emulation and vast wealth of kings; the lake hollowed out of the earth to be a receptacle for the Nile’s overflow; and elsewhere the river’s narrow channel and profound depth which no line of the explorer can penetrate. He then came to Elephantine and Syene, formerly the limits of the Roman empire, which now extends to the Red Sea.

Getting Spatial Audio from Unity Session Recorders

There are a number of VR session recorders available for purchase or free download, and most boast that they can record ”spatial audio.” This is not true by default. These products have been around for several years, and the fact that the issue is not a major topic on forums seems to stem from the fact that either 1) people who use these recorders don’t seem to care about the spatial audio in their games, 2) their audio is being generated using middleware (wwise, FMOD) which will not be captured using the default ”audio listener” anyway and so are already using workarounds, or 3) those that do care about spatial audio create custom workflows or use custom game engines.  I generally use middleware, but I have started to explore how to create custom spatial audio using the default audio tools available.

In this post, I am going to show you how to do this using the Helios session recorder, but the same process will likely work for any asset that records the default audio listener data.

Why Helios?

Honest answer: it is what I have and know how to use. There is no other reason and other tools are fine. Helios is an inexpensive session recorder that is works well with Pegasus and Gaia.  It can render 360, stereographic, and ”little planet” videos, and uses Google’s Spatial Media Metadata injector to inject the 360 data.

The problem with recording spatial audio using the audio listener or raw output

The audio listener is what is recorded using the project Audio settings.  Helios records the audiolistener output and then re-encodes it to match with the frame rate. Possible audio outputs are stereo, quad, 7.1, raw, etc.  When recording audio:

Unity’s audio system will only provide the raw source sound as a stereo signal (even when the source is mono or multi-channel in which case up- or down-mixing is used).

Unity documentation states that this output will always be down-mixed stereo, which can never be ambisonic.  Ambisonic audio is minimum 4 channels.

The workaround

We can use the Google/Youtube First Order Ambisonics Tutorial reaper project to slyly ”convert” the binaural stereo to 4 channel.  This will not add lost spatial information, but it will replace enough of the spatial effects in your 360 video to make it satisfying to poke around the video.  At any rate, it is worlds better than no spatial audio in your 360 video.


  1. Record your session in whatever tool you are using (including session audio)
  2. Find the session audio (in helios it is in your sessions folder)
  3. Click on it to see the number of channels.
    1. If you are new to audio, look at the stripes.  2 stripes? stereo.  4 stripes?  quad or ambisonic.stereo
    2. Assuming you have the stereo file, you should now convert it to 4 channel ambisonic.
  4. Follow the tutorial, install all of the binaural plugins and open the reaper project
  5.  Put your 2 channel sound file in the ”encoder” track at 0:00.  Select the region containing only the audio for your track.  It should be highlighted white.reaperexample.PNG
  6. Now, render your track.  In the tutorial, it shows you how to render the full movie in mp4/mov/etc, but we would like Helios to sync it up for us as a ”soundtrack”, so we will save it as a 4 channel wav.  Go to file/render and set it up like below.  For ease, put the newly rendered file in the directory where the session audio was found.  It will make it easier to find later.render
  7.  Assuming all has gone well, take a look at your new file in Unity.  Check the channel count and check ”Ambisonic” in the checkbox.4channel
  8. Add this fresh file to your soundtrack soundtrack
  9. Render your file as usual. When you go to inject the metadata, you should have no trouble injecting the spatial audio this time.checkbox.PNG
  10.  The effect of this process will be to hear the spatial audio when exploring your 360 video of your game/walkthrough/VR experience.

Echoes in Various Ancient Texts


Night began to wane, [385] yet the fleet of the Hellenes in no way attempted to put forth by stealth. When, however, radiant Day with her white horses shone over all the land, a loud cheer like a song of triumph first rang out from the Hellenes, and, at the same instant, [390] clear from the island crags, an echo returned an answering cry. Terror fell on all the barbarians, balked of their purpose; for then the Hellenes chanted their solemn paean, not as in flight, but as men rushing to the onset with the courage of gallant hearts.

40 As to Hylas and Herakles, compare Ap. Rhod., Argon. i.1207ff.; Theocritus xiii.; Ant. Lib. 26; Orphica, Argonautica 646ff.; Valerius Flaccus, Argon. iii.521ff.; Prop. i.20.17ff.; Hyginus, Fab. 14; Scriptores rerum mythicarum Latini, ed. Bode, i. pp. 18, 140 (First Vatican Mythographer 49; Second Vatican Mythographer 199). It is said that down to comparatively late times the natives continued to sacrifice to Hylas at the spring where he had disappeared, that the priest used to call on him thrice by name, and that the echo answered thrice (Ant. Lib. 26).


[995] Echo, the nymph of Cithaeron, returns thy words, which resound beneath the dark vaults of the thick foliage and in the midst of the rocks of the forest; the ivy [1000] enlaces thy brow with its tendrils charged with flowers

Hymn 19 to Pan

Muse, tell me about Pan, the dear son of Hermes, with his goat’s feet and two horns —a lover of merry noise. Through wooded glades he wanders with dancing nymphs who foot it on some sheer cliff’s edge, [5] calling upon Pan, the shepherd-god, long-haired, unkempt. He has every snowy crest and the mountain peaks and rocky crests for his domain; hither and thither he goes through the close thickets, now lured by soft streams, [10] and now he presses on amongst towering crags and climbs up to the highest peak that overlooks the flocks. Often he courses through the glistening high mountains, and often on the shouldered hills he speeds along slaying wild beasts, this keen-eyed god. Only at evening, [15] as he returns from the chase, he sounds his note, playing sweet and low on his pipes of reed: not even she could excel him in melody —that bird who in flower-laden spring pouring forth her lament utters honey-voiced song amid the leaves. At that hour the clear-voiced nymphs are with him and [20] move with nimble feet, singing by some spring of dark water, while Echo wails about the mountain-top, and the god on this side or on that of the choirs, or at times sidling into the midst, plies it nimbly with his feet. On his back he wears a spotted lynx-pelt, and he delights in high-pitched songs [25] in a soft meadow where crocuses and sweet-smelling hyacinths bloom at random in the grass.

Plato, Republic

to hold their heads unmoved through life?” “And again, would not the same be true of the objects carried past them?” “Surely.” “If then they were able to talk to one another, do you not think that they would suppose that in naming the things that they saw1 they were naming the passing objects?” “Necessarily.” “And if their prison had an echo2 from the wall opposite them, when one of the passersby uttered a sound, do you think that they would suppose anything else than the passing shadow to be the speaker?” “By Zeus, I do not,” said he. “Then in every way

1 Cf. Parmen. 130 c, Tim. 51 B, 52 A, and my De Platonis Idearum doctrina, pp. 24-25; also E. Hoffmann in Wochenschrift f. klass. Phil. xxxvi. (1919) pp. 196-197. As we use the word tree of the trees we see, though the reality (αὐτὸἔστι) is the idea of a tree, so they would speak of the shadows as the world, though the real reference unknown to them would be to the objects that cause the shadows, and back of the objects to the things of the “real” world of which they are copies. The general meaning, which is quite certain, is that they wold suppose the shadows to be the realities. The text and the precise turn of expression are doubtful. See crit. note.παριόντα is intentionally ambiguous in its application to the shadows or to the objects which cast them. They suppose that the names refer to the passing shadows, but (as we know) they really apply to the objects. Ideas and particulars are homonymous. Assuming a slight illogicality we can get somewhat the same meaning from the text ταὐτά. “Do you not think that they would identify the passing objects (which strictly speaking they do not know) with what they saw?” Cf. also P. Corssen, Philologische Wochenschrift, 1913, p. 286. He prefers οὐκαὐτά and renders: “Sie würden in dem, was sie sähen, das Vorübergehende selbst zu benennen glauben.”

2 The echo and the voices (515 A) merely complete the picture.

Plato, Phaedrus

then the fountain of that stream which Zeus, when he was in love with Ganymede, called “desire” flows copiously upon the lover; and some of it flows into him, and some, when he is filled, overflows outside; and just as the wind or an echo rebounds from smooth, hard surfaces and returns whence it came, so the stream of beauty passes back into the beautiful one through the eyes, the natural inlet to the soul, where

Virgil, Aeneid

98. “Vocemvolutant” is said 5. 149 of the shores that echo the sound, a sense which some have wished to impart here, making ‘perampla’ one word.


Scarce had he said, when on the mountain’s brow
We saw the giant shepherd stalk before
His following flock, and leading to the shore:
A monstrous bulk, deform’d, depriv’d of sight;
His staff a trunk of pine, to guide his steps aright.
His pond’rous whistle from his neck descends;
His woolly care their pensive lord attends:
This only solace his hard fortune sends.
Soon as he reach’d the shore and touch’d the waves,
From his bor’d eye the gutt’ring blood he laves:
He gnash’d his teeth, and groan’d; thro’ seas he strides,
And scarce the topmost billows touch’d his sides.

Seiz’d with a sudden fear, we run to sea,
The cables cut, and silent haste away;
The well-deserving stranger entertain;
Then, buckling to the work, our oars divide the main.
The giant harken’d to the dashing sound:
But, when our vessels out of reach he found,
He strided onward, and in vain essay’d
Th’ Ionian deep, and durst no farther wade.
With that he roar’d aloud: the dreadful cry
Shakes earth, and air, and seas; the billows fly
Before the bellowing noise to distant Italy.
The neigh’ring Aetna trembling all around,
The winding caverns echo to the sound.


Better by far to round the distant goal
of the Trinacrian headlands, veering wide
from thy true course, than ever thou shouldst see
that shapeless Scylla in her vaulted cave,
where grim rocks echo her dark sea-dogs’ roar.
Yea, more, if aught of prescience be bestowed
on Helenus, if trusted prophet he,
and Phoebus to his heart true voice have given,
o goddess-born, one counsel chief of all
I tell thee oft, and urge it o’er and o’er.
To Juno’s godhead lift thy Ioudest prayer;
to Juno chant a fervent votive song,
and with obedient offering persuade
that potent Queen. So shalt thou, triumphing,
to Italy be sped, and leave behind


M. Annaeus Lucanus, Pharsalia

By seas inviolate, one bank of sand
Far from the coast arose; there watched in vain
The storm-tossed mariners, their keel aground,
No shore descrying. Thus in sea were lost
Some portion, but the major part by helm
And rudder guided, and by pilots’ hands
Who knew the devious channels, safe at length
Floated the marsh of Triton loved (as saith
The fable) by that god, whose sounding shell2
All seas and shores re-echo; and by her,
Pallas, who springing from her father’s head
First lit on Libya, nearest land to heaven,
(As by its heat is proved); here on the brink
She stood, reflected in the placid wave
And called herself Tritonis. Lethe’s flood
Flows silent near, in fable from a source
Infernal sprung, oblivion in his stream;
Here, too, that garden of the Hesperids,
Its boughs all golden, where of old his watch
The sleepless dragon held. Shame be on him
Who calls upon the poet for the proof
Of that which in the ancient days befell;
But here were golden groves by yellow growth
Weighed down in richness, here a maiden band
Were guardians; and a serpent, on whose eyes
Sleep never fell, was coiled around the trees,
Whose branches bowed beneath their ruddy load.


Sound and Acoustics from Vitruvius Pollio’s The Ten Books on Architecture


1. AFTER the forum has been arranged, next, for the purpose of seeing plays or festivals of the immortal gods, a site as healthy as possible should be selected for the theatre, in accordance with what has been written in the first book, on the principles of healthfulness in the sites of cities. For when plays are given, the spectators, with their wives and children, sit through them spellbound, and their bodies, motionless from enjoyment, have the pores open, into which blowing winds find their way. If these winds come from marshy districts or from other unwholesome quarters, they will introduce noxious exhalations into the system. Hence, such faults will be avoided if the site of the theatre is somewhat carefully selected

4. The curved cross-aisles should be constructed in proportionate relation, it is thought, to the height of the theatre, but not higher than the footway of the passage is broad. If they are loftier, they will throw back the voice and drive it away from the upper portion, thus preventing the case-endings of words from reaching with distinct meaning the ears of those who are in the uppermost seats above the cross-aisles. In short, it should be so contrived that a line drawn from the lowest to the highest seat will touch the top edges and angles of all the seats. Thus the voice will meet with no obstruction.

5. The different entrances ought to be numerous and spacious, the upper not connected with the lower, but built in a continuous straight line from all parts of the house, without turnings, so that the people may not be crowded together when let out from shows, but may have separate exits from all parts without obstructions. Particular pains must also be taken that the site be not a “deaf” one, but one through which the voice can range with the greatest clearness. This can be brought about if a site is selected where there is no obstruction due to echo.

6. Voice is a flowing breath of air, perceptible to the hearing by contact. It moves in an endless number of circular rounds, like the innumerably increasing circular waves which appear when a stone is thrown into smooth water, and which keep on spreading indefinitely from the centre unless interrupted by narrow limits, or by some obstruction which prevents such waves from reaching their end in due formation. When they are interrupted by obstructions, the first waves, flowing back, break up the formation of those which follow.

7. In the same manner the voice executes its movements in concentric circles; but while in the case of water the circles move horizontally on a plane surface, the voice not only proceeds horizontally, but also ascends vertically by regular stages. Therefore, as in the case of the waves formed in the water, so it is in the case of the voice: the first wave, when there is no obstruction to interrupt it, does not break up the second or the following waves, but they all reach the ears of the lowest and highest spectators without an echo.

8. Hence the ancient architects, following in the footsteps of nature, perfected the ascending rows of seats in theatres from their investigations of the ascending voice, and, by means of the canonical theory of the mathematicians and that of the musicians, endeavoured to make every voice uttered on the stage come with greater clearness and sweetness to the ears of the audience. For just as musical instruments are brought to perfection of clearness in the sound of their strings by means of bronze plates or horn so the ancients devised methods of increasing the power of the voice in theatres through the application of harmonics.


. IN accordance with the foregoing investigations on mathematical principles, let bronze vessels be made, proportionate to the size of the theatre, and let them be so fashioned that, when touched, they may produce with one another the notes of the fourth, the fifth, and so on up to the double octave. Then, having constructed niches in between the seats of the theatre, let the vessels be arranged in them, in accordance with musical laws, in such a way that they nowhere touch the wall, but have a clear space all round them and room over their tops. They should be set upside down, and be supported on the side facing the stage by wedges not less than half a foot high. Opposite each niche, apertures should be left in the surface of the seat next below, two feet long and half a foot deep.

2. The arrangement of these vessels, with reference to the situations in which they should be placed, may be described as follows. If the theatre be of no great size, mark out a horizontal range halfway up, and in it construct thirteen arched niches with twelve equal spaces between them, so that of the above mentioned “echea” those which give the note nete hyperbolaeon may be placed first on each side, in the niches which are at the extreme ends; next to the ends and a fourth below in pitch, the note nete diezeugmenon; third, paramese, a fourth below; fourth, nete synhemmenon; fifth, mese, a fourth below; sixth, hypate meson, a fourth below; and in the middle and another fourth below, one vessel giving the note hypate hypaton.

3. On this principle of arrangement, the voice, uttered from the stage as from a centre, and spreading and striking against the cavities of the different vessels, as it comes in contact with them, will be increased in clearness of sound, and will wake an harmonious note in unison with itself. But if the theatre be rather large, let its height be divided into four parts, so that three horizontal ranges of niches may be marked out and constructed: one for the enharmonic, another for the chromatic, and the third for the diatonic system. Beginning with the bottom range, let the arrangement be as described above in the case of a smaller theatre, but on the enharmonic system.

In the middle range, place first at the extreme ends the vessels which give the note of the chromatic hyperbolaeon;

next to them, those which give the chromatic diezeugmenon, a fourth below; third, the chromatic synhemmenon; fourth, the chromatic meson, a fourth below; fifth, the chromatic hypaton, a fourth below; sixth, the paramese, for this is both the concord of the fifth to the chromatic hyperbolaeon, and the concord 1 of the chromatic synhemmenon.

1 Codd. diatessaron, which is impossible, paramese being the concord of the fourth to the chromatic meson, and identical with the chromatic synhemmenon.

5. No vessel is to be placed in the middle, for the reason that there is no other note in the chromatic system that forms à natural concord of sound. In the highest division and range of niches, place at the extreme ends vessels fashioned so as to give the note of the diatonic hyperbolaeon; next, the diatonic diezeugmenon, a fourth below; third, the diatonic synhemmenon; fourth, the diatonic meson, a fourth below; fifth, the diatonic hypaton, a fourth below; sixth, the proslambanomenos, a fourth below; in the middle, the note mese, for this is both the octave to proslambanomenos, and the concord of the fifth to the diatonic hypaton.

6. Whoever wishes to carry out these principles with ease, has only to consult the scheme at the end of this book, drawn up in accordance with the laws of music. It was left by Aristoxenus, who with great ability and labour classified and arranged in it the different modes. In accordance with it, and by giving heed to these theories, one can easily bring a theatre to perfection, from the point of view of the nature of the voice, so as to give pleasure to the audience.

7. Somebody will perhaps say that many theatres are built every year in Rome, and that in them no attention at all is paid to these principles; but he will be in error, from the fact that all our public theatres made of wood contain a great deal of boarding, which must be resonant. This may be observed from the behaviour of those who sing to the lyre, who, when they wish to sing in a higher key, turn towards the folding doors on the stage, and thus by their aid are reinforced with a sound in harmony with the voice. But when theatres are built of solid materials like masonry, stone, or marble, which cannot be resonant, then the principles of the “echea” must be applied.

8. If, however, it is asked in what theatre these vessels have been employed, we cannot point to any in Rome itself, but only to those in the districts of Italy and in a good many Greek states. We have also the evidence of Lucius Mummius, who, after destroying the theatre in Corinth, brought its bronze vessels to Rome, and made a dedicatory offering at the temple of Luna with the money obtained from the sale of them. Besides, many skilful architects, in constructing theatres in small towns, have, for lack of means, taken large jars made of clay, but similarly resonant, and have produced very advantageous results by arranging them on the principles described.

1. this having been settled with the greatest pains and skill, we must see to it, with still greater care, that a site has been selected where the voice has a gentle fall, and is not driven back with a recoil so as to convey an indistinct meaning to the ear. There are some places which from their very nature interfere with the course of the voice, as for instance the dissonant, which are termed in Greek κατηχοῦντες; the circumsonant, which with them are named περιηχοῦντες; again the resonant, which are termed ἀντηχοῦντες; and the consonant, which they call συνηχοῦντες. The dissonant are those places in which the first sound uttered that is carried up high, strikes against solid bodies above, and, being driven back, checks as it sinks to the bottom the rise of the succeeding sound.

2. The circumsonant are those in which the voice spreads all round, and then is forced into the middle, where it dissolves, the case-endings are not heard, and it dies away there in sounds of indistinct meaning. The resonant are those in which it comes into contact with some solid substance and recoils, thus producing an echo, and making the terminations of cases sound double. The consonant are those in which it is supported from below, increases as it goes up, and reaches the ears in words which are distinct and clear in tone. Hence, if there has been careful attention in the selection of the site, the effect of the voice will, through this precaution, be perfectly suited to the purposes of a theatre. The drawings of the plans may be distinguished from each other by this difference, that theatres designed from squares are meant to be used by Greeks, while Roman theatres are designed equilateral triangles. Whoever is willing to follow these directions will be able to construct perfectly correct theatres.



3. Under the roof-beam he fixed a wooden channel in which he arranged a block of pulleys. He carried the cord along the channel to the corner, where he set up some small piping. Into this a[274] leaden ball, attached to the cord, was made to descend. As the weight fell into the narrow limits of the pipe, it naturally compressed the enclosed air, and, as its fall was rapid, it forced the mass of compressed air through the outlet into the open air, thus producing a distinct sound by the concussion.

4. Hence, Ctesibius, observing that sounds and tones were produced by the contact between the free air and that which was forced from the pipe, made use of this principle in the construction of the first water organs. He also devised methods of raising water, automatic contrivances, and amusing things of many kinds, including among them the construction of water clocks. He began by making an orifice in a piece of gold, or by perforating a gem, because these substances are not worn by the action of water, and do not collect dirt so as to get stopped up.


1. With regard to water organs, however, I shall not fail with all possible brevity and precision to touch upon their principles, and to give a sufficient description of them. A wooden base is constructed, and on it is set an altar-shaped box made of bronze. Uprights, fastened together like ladders, are set up on the base, to the right and to the left (of the altar). They hold the bronze pump-cylinders, the moveable bottoms of which, carefully turned on a lathe, have iron elbows fastened to their centres and jointed to levers, and are wrapped in fleeces of wool. In the tops of the cylinders are openings, each about three digits in diameter. Close to these openings are bronze dolphins, mounted on joints and holding chains in their mouths, from which hang cymbal-shaped valves, let down under the openings in the cylinders.

2. Inside the altar, which holds the water, is a regulator shaped like an inverted funnel, under which there are cubes, each about three digits high, keeping a free space below between the lips of the regulator and the bottom of the altar. Tightly fixed on the neck of the regulator is the windchest, which supports the principal part of the contrivance, called in Greek the κανων μουσικὁς. Running longitudinally, there are four channels in it if it is a tetrachord; six, if it is a hexachord; eight, if it is an octachord.

3. Each of the channels has a cock in it, furnished with an iron handle. These handles, when turned, open ventholes from the windchest into the channels. From the channels to the canon there are vertical openings corresponding to ventholes in a board above, which board is termed πἱναξ in Greek. Between this board and the canon are inserted sliders, pierced with holes to correspond, and rubbed with oil so that they can be easily moved and slid back into place again. They close the above-mentioned openings, and are called the plinths. Their going and coming now closes and now opens the holes.[300]

4. These sliders have iron jacks fixed to them, and connected with the keys, and the keys, when touched, make the sliders move regularly. To the upper surface of the openings in the board, where the wind finds egress from the channels, rings are soldered, and into them the reeds of all the organ pipes are inserted. From the cylinders there are connecting pipes attached to the neck of the regulator, and directed towards the ventholes in the windchest. In the pipes are valves, turned on a lathe, and set (where the pipes are connected with the cylinders). When the windchest has received the air, these valves will stop up the openings, and prevent the wind from coming back again.

5. So, when the levers are raised, the elbows draw down the bottoms of the cylinders as far as they can go; and the dolphins, which are mounted on joints, let the cymbals fall into the cylinders, thus filling the interiors with air. Then the elbows, raising the bottoms within the cylinders by repeated and violent blows, and stopping the openings above by means of the cymbals, compress the air which is enclosed in the cylinders, and force it into the pipes, through which it runs into the regulator, and through its neck into the windchest. With a stronger motion of the levers, the air is still more compressed, streams through the apertures of the cocks, and fills the channels with wind.

6. So, when the keys, touched by the hand, drive the sliders forward and draw them back regularly, alternately stopping and opening the holes, they produce resonant sounds in a great variety of melodies conforming to the laws of music.

With my best efforts I have striven to set forth an obscure subject clearly in writing, but the theory of it is not easy, nor readily understood by all, save only those who have had some practice in things of this kind. If anybody has failed to understand it, he will certainly find, when he comes to know the thing itself, that it is carefully and exquisitely contrived in all respects.


1. Beams of very generous length are selected, and upon them are nailed socket-pieces in which windlasses are inserted. Midway along their length the beams are incised and cut away to form framings, and in these cuttings the capitals of the catapults are inserted, and prevented by wedges from moving when the stretching is going on. Then the bronze boxes are inserted into the capitals, and the little iron bolts, which the Greeks call ἑπιξυγἱδες, are put in their places in the boxes.

2. Next, the loops of the strings are put through the holes in the capitals, and passed through to the other side; next, they are put upon the windlasses, and wound round them in order that[309] the strings, stretched out taut on them by means of the handspikes, on being struck by the hand, may respond with the same sound on both sides. Then they are wedged tightly into the holes so that they cannot slacken. So, in the same manner, they are passed through to the other side, and stretched taut on the windlasses by means of the handspikes until they give the same sound. Thus with tight wedging, catapults are tuned to the proper pitch by musical sense of hearing.

On these things I have said what I could. There is left for me, in the matter of sieges, to explain how generals can win victories and cities be defended, by means of machinery.

Examples of Hearing Acoustics in Plato

Then, my dear Crito, there was universal applause of the speakers and their words, and
what with laughing and clapping of hands and rejoicings the two men were quite
overpowered; for hitherto their partisans only had cheered at each successive hit, but
now the whole company shouted with delight until the columns of the Lyceum returned
the sound, seeming to sympathize in their joy. – Plato

….when he was in love with Ganymede named Desire, overflows upon the lover, and someenters into his soul, and some when he is filled flows out again; and as a breeze or an echo rebounds from the smooth rocks and returns whence it came, so does the stream
of beauty, passing through the eyes which are the windows of the soul, come back to
the beautiful one; there arriving and quickening the passages of the wings, watering
them and inclining them to grow, and filling the soul of the beloved also with love

Some persons say that the Sophists are the corrupters of youth; but is not public opinion the real Sophist who is everywhere present—in those very persons, in the assembly, in the courts, in the camp, in the applauses and hisses of the theatre re-echoed by the surrounding hills? Will not a young man’s heart leap amid these discordant sounds? and will any education save him from being carried away by the torrent?

They are ourselves, I replied; and they see only the shadows of the images which the fire throws on the wall of the den; to these they give names, and if we add an echo which returns from the wall, the voices of the passengers will seem to proceed from the shadows. Suppose now that you suddenly turn them round and make them look with pain and grief to themselves at the real images; will they believe them to be real?

When they meet together, and the world sits down at an assembly, or in a court of law,
or a theatre, or a camp, or in any other popular resort, and there is a great uproar, and
they praise some things which are being said or done, and blame other things, equally
exaggerating both, shouting and clapping their hands, and the echo of the rocks and
the place in which they are assembled redoubles the sound of the praise or blame

And if they were able to converse with one another, would they not suppose that they
were naming what was actually before them?/Very true./And suppose further that the prison had an echo which came from the other side, would they not be sure to fancy when one of the passers-by spoke that the voice which they heard came from the passing shadow?/No question, he replied./To them, I said, the truth would be literally nothing but the shadows of the images./That is certain.

Prodicus was saying, for he seems to me to be an all-wise and
inspired man; but I was not able to get into the inner circle, and his fine deep voice
made an echo in the room which rendered his words inaudible

The land between the harbour and the sea was surrounded by a wall, and was crowded with dwellings, and the harbour and canal resounded with the din of human voices.