This is by no means a dumb question, many very smart people
have tried to answer this question over the years with varying
degrees of success.
Your ears work together as a system in getting sound data to
the brain. The aurical (the part of your ear on the outside of
your head) and the ear canal both play a part in your directional
hearing ability. The physical construction of these parts (along
with the overall shape of your head) cause slight frequency
response changes in sounds that come from different directions.
Your brain picks up on these small frequency response differences
and gives you a location for the sound direction.
So in answer to your question, a two speaker setup or a standard
headphone playback doesn't take into account these frequence
response variations that give your brain the directional clues it needs
to locate the sound.
Now there is a whole industry dedicated to the effort of producing
simulated 3d positioned audio with 2 sound sources (either speakers
or headphones) by emulating these frequency response changes.
The HRTF (Head Related Transfer Function) is a mathmatical model
that describes these frequency response changes. This model was
developed by using a dummy head (see KEMAR) with mics down
where the eardrums would be and measuring the frequency response
changes as sound came at the dummy from different directions.
So now we have these tables that tell us if a sound is coming from the
right rear it will have a specific frequency response in the right ear and
a different response in the left ear, so if we apply this function to the
audio data before we play it the sound should come from the right
rear.
This is a great theory but it doesn't work vary well in practice. There
are too many real world variables to get it to work reliably over a large
subset of people including:
- everyones head and ears are different giving each person a unique HRTF
that can only be approximated by an "average" HRTF
- If you are using speakers as the sound source then the persons head
position relative to the speakers is critical, and uncontrollable.
- Headphones are much better for controlling the audio reaching the
eardrums,
but there is a tendancy to get a things foating inside my head effect.
On the other hand a real multi speaker setup really can put sounds behind
you
and your brain can do its own sound positioning magic giving a much
more realistic experiance.
As you can tell this question pushes one of my buttons, but I hope I've
answered your question somewhere in my ranting.
Regards,
David Sowa
----- Original Message -----
From: "PrinceGaz" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, February 29, 2000 10:12 AM
Subject: MD: Surround sound
>
> Hi guys, if you think I'm stupid please be gentle with me!
>
> A big thing is made these days of Dolby Pro-Logic Dolby Digital and
> all sorts of cinema surround sound systems. So I'm gonna ask a
> really stupid question which I would really like a serious answer
> to.
>
> We have two ears, a left and a right ear, so what advantage can be
> gained by using more than left and right speakers / headphones?
>
> I know I'm gonna get humiliated by asking this but I can't hold off
> asking any longer. I know in the cinema the sound may seem to
> come from behind because it did-- but our two ears received the
> sound from all angles and our brain gave us the surround effect.
>
> Cheers,
> PrinceGaz -- "if it harms none, do what you will"
> Email: [EMAIL PROTECTED]
> Website: http://website.lineone.net/~princegaz/
> ICQ: 36892193
>
> Earn a minimum of $20 per hour by watching ads on the net!
> Visit http://www.bepaid.com/users.rhtml?REFID=10164669
>
>
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