silver@ENIAC.SEAS.UPENN.EDU (Andy Silverman) (02/13/90)
Well, I have this Yamaha PTX-8 drum pad set, and they say that the sampling involved is "12-bit companded PCM." What exactly does this mean? The sounds that come out of the thing are so cheesy (even on an extra Waveform ROM cartridge) that I never use them anymore, instead using to trigger a Roland R-5 via MIDI. Andy Silverman silver@eniac.seas.upenn.edu
adamson@ITD.NRL.NAVY.MIL (Brian Adamson) (02/13/90)
Companded probably means they are really using 8-bit A/D conversion and then using some kind of dynamic range assignment rule supposedly optimized for drum sounds to try to get the same dynamic range as you would get if you had used a 12 bit A/D converter to start with. Although this may give you some added dynamic range (sort of), it does not change the signal-to-noise ratio max that can be achieved using only 8 bit conversion (approx 45-50 dB). That may be part of the problem. I posted a message a little while ago about linear samples versus companded (compressed according to u-law, A-law, etc). Hope this helps, Brian Adamson
kg19+@ANDREW.CMU.EDU (Kurt A. Geisel) (02/13/90)
How does companding get more dynamic range out of PLAYBACK circuitry that is only 8-bits wide? By having a seperate overall amplitude control channel? - Kurt Kurt Geisel SNAIL : Carnegie Mellon University 65 Lambeth Dr. ARPA : kg19+@andrew.cmu.edu Pittsburgh, PA 15241 UUCP : uunet!nfsun!kgeisel "We just need to short-circuit the continuum on a BIX : kgeisel 5 or 6 parsec level." - Forbidden Planet
JEFF@UTCVM.BITNET (Jeffrey R Kell) (02/13/90)
On Mon, 12 Feb 90 20:18:35 EST Kurt A. Geisel said: >How does companding get more dynamic range out of PLAYBACK circuitry >that is only 8-bits wide? By having a seperate overall amplitude >control channel? No, you encode/decode sample values on a non-linear scale, most likely some exponential function. If the A/D D/A conversions are strictly limited to 8-bit you would have to do this on the analog side; for example placing a dBx compander chip set on the analog side of the converters. The magic is the non-linear signal treatment as opposed to simply reducing resolution or padding the signal. <Jeff> ****************************** * If the first person who answers the phone cannot answer your * question, it's a bureaucracy. ******************************