Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!gem.mps.ohio-state.edu!tut.cis.ohio-state.edu!bloom-beacon!mcgill-vision!clyde!maxwell!jean From: jean@maxwell.Concordia.CA ( JEAN GOULET ) Newsgroups: comp.dsp Subject: Re: ASSP Workshop on Audio and Acoustics Summary: How much compression did they get? Message-ID: <1506@clyde.Concordia.CA> Date: 25 Oct 89 07:24:17 GMT References: Sender: news@Clyde.Concordia.CA Reply-To: jean@maxwell.Concordia.Ca ( JEAN GOULET ) Organization: Concordia University, Montreal Quebec Lines: 47 In article 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