🚀 go-pugleaf

In article <GDA.89Oct23163049@creare.creare.UUCP> gda@creare.creare.UUCP (Gray Abbott) writes:
>
>The wideband coding session dealt with compressing music/high quality
>speech/data for storage or transmission.  Several papers focused on
>using psychoacoustic/auditory models to determine what part of the
>signal is inaudible, due to masking, so that it can be discarded without
>perceptually harming the signal.  Some interesting hardware and algorithms
>here, including a wave digital filter implementation a filterbank,
>by Ulrich Sauvagerd.

Do you remember what kind of compression ratio they managed to achieve?
I've been looking for ways of recording as much decent-quality audio into
my limited RAM as possible, but the papers I've seen focus on minimizing speech
bandwidth.  They tend to remove as much information from the speech
signal as they can get away with, until the words are barely comprehensible.
I've only tried some simple algorithms which can reconstruct the input data
exactly after expansion, rather than those which discard parts of the
signal.  I suppose that part of the reason for that is that I went through
so much trouble at making my ADC as noise-free as possible that it would
seem counterproductive to throw away parts of the ADC's output.  Plus it's
hard to anticipate the consequences of doing DSP on that kind of compressed
data, since it will be likely that some frequency components will have been
lost (take for example pitch-shifting a music instrument; while you might kill
some frequency components because they're perceptually insignificant at the
original pitch, that may not be the case after you shift to a new pitch...).

>       [...]                                   Which brings me to another
>paper, by Lehnert and Blauert, in which they completely simulate a concert
>hall, using ray tracing, and combine that with head and pinna transforms.
>Alas, this system is non-real-time (overnight processing on a PC/AT), but
>it's just what I always wanted to do...

I take it that the ray tracing you're talking about is for tracing acoustic
waves, and not light waves, as in ray tracing for graphics.  I'm asking  
because if they really wanted to recreate the concert hall experience, they'd
have to do both kinds of ray tracing.  Then they could do the Virtual Reality
thing by fitting the user with a helmet having stereo headphones and stereo
goggles, with each goggle lens displaying a high-quality color image of the
scenery around the user depending on which direction their head is pointing.
Guess we'll have to wait until they can fit a battery-operated supercomputer
with Gigabytes (Terabytes?) of RAM in a walkman-sized box...

                                             Jean Goulet
                                             Electrical Engineering
                                             Class of '89
                                             Concordia University
                                             Montreal, Canada