--- In "Barry Blesser"
<> wrote:
>
> Having read some of the discussions on reproducing
> an ambient sound field, it might be useful to
> explore some of the theoretical issues. All
> technical solutions are crude compromises.
> Although Chapter 6 of the book, "Spaces Speak,
> Are Your Listening?" explores the issues for music,
> the same situation presents itself with all natural
> sound field recording.
>
> The central problem is that one is trying to
> reproduce sound in a volume of space.
> Microphones and microphone capture and reproduce
> sound at a few discrete points. Mapping discrete
> points into spatial volumes is THE problem.
>
> In this sense, the compromise is always in the size
> of the sweet spot, the volume in which the
> reproduction is sufficiently accurate. At on
> extreme, we have the volume at the entrance to the
> two ears, which approximates discrete points in space.
> At the other extreme, we have a room where many
> people can be in a large sweet spot. In this case,
> a perfect reproduction would allow a listener to walk
> through the reproduction space as if he/she were
> walking through the original space. Each of the two
> extremes presents two different classes of problems.
>
> Take the large sweet-spot first. Perfect reproduction
> requires the sound field to be sampled in time AND
> space. Based on the Nyquist theorem, one has to same
> at twice the highest bandwidth. Assume 10 kHz for
> discussion. But one also has to sample in space.
> The wavelength of 10 kHz is about 0.1 inches.
> Therefore a 1 cubic foot volume requires about 10**9
> points to be sampled. You get the idea. The numbers
> become so large, that perfect reproduction is clearly
> impossible in a large volume. Moreover, the reproduced
> sound field takes place in a space that has its own
> acoustics. And each listening space is unique.
>
> Now take the other extreme, which is binaural recording.
> The sweet spot covers only one individual. But that too
> has two issues. An individual's outer ears, the pinna,
> are unique and the recording process using a dummy head
> needs to have ears that match those of the listener.
> Moreover, with headphones, the sound field moves as
> the listener turns his head. Once we introduce a moving
> head, we are enlarging the volume in which the sound
> field needs to be captured and reproduced.
>
> Having established that a perfect production is
> impossible, we are now left with the question of how
> to choose a compromise.
>
> One obvious choice is to borrow the commercial technology
> of 5.1 home-theater. Another choice is to borrow some
> of the more advanced laboratory systems, such as
> ambisonics, holophony, or head-tracking binaural.
>
> In conclusion, the critical question is deciding the size
> of the sweet-spot. Is the reproduction intended for one
> listener or many? Is the reproduction equipment part of
> the recording assumptions such that a listener must setup
> a particular system in order to listen to the recording?
>
> Make your compromises but be clear about their assumptions.
> Even the best systems are crude compromises.
>
This reminds me of the discussion years ago about getting "true
sound" from stereo speakers. Every manufacturer tried something. Some
attempted to create a "straight wire with gain." Others accepted
that "colored" sound was inevitable and characterized their speakers
accordingly.
Then, of course, along came digital recording! What a tempest that
stirred! The step from analogue LPs, which really hadn't changed much
since Edison's day, was HUGE for many.
I tend towards recorded sounds that intentionally carry a thematic
element. That is, I try to use sound as a means of conveying a
particular feeling or particular shade of perception. This, I'm sure,
comes from my background as a novelist and story teller.
I respect "pure sound" as much as anyone, but I honestly don't know
if that's really possible. All I want to do is control the variables
to an extent that allows me to accomplish my goal.
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