Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!daver!intersil!hamilton
From: hamilton@intersil.uucp
Newsgroups: comp.sys.amiga.audio
Subject: Re: CHEAP 16-bit STEREO sound samplers
Message-ID: <282.2865f3ac@intersil.uucp>
Date: 24 Jun 91 13:29:15 GMT
References: <17787@chaph.usc.edu> <744@cronos.metaphor.com> <8674@jhunix.HCF.JHU.EDU> <91166.165734DXB132@psuvm.psu.edu>
Organization: Harris Semiconductor, Santa Clara CA
Lines: 32

I've been giving some thought to designing a "cheap" 16 bit audio digitizer
for the Amiga, but the more one thinks about it, the more expensive it gets.
Here's how it seems to go:

Why do you want 16 bits?  Better, "CD-like" sound quality.  OK, that means
40K+ samples/sec/channel (we want stereo, right?).  Well, at a transfer
rate of 16bits*2channels*40000=160,000 bytes/sec, the parallel, serial, and
yes even mouse port is out.  So now we're talking an internal autoconfig
card.  Now let's look at the size of the data we're going to be dealing with:
a 10 second, stereo, CD-quality sound bite takes 1.5 megabytes.  A 4 minute
song is 36 megabytes.  That's a lot of data, moving at a fairly fast rate.
For this system to be practical to use, we need a DSP chip to compress the
data size and slow down the data rate.  The DSP chip is also useful because 
people will probably want to DO SOMETHING with the sound once they've sampled
it, and a dedicated DSP processor is the only way to do any sort-of significant
number crunching on digital audio.

Additionally, people would probably like to hear the sample.  So now we need
a pair of A/D converters.  Finally, you need to put all this hardware
together along with some-sort of practical DMA scheme so the Amiga remains
multitasking, and also write a *lot* of software to make all this work
and be easy enough to use so that people will buy it.  The hardware's not
trivial either-you need decent anti-aliasing filters for the A/Ds and D/As,
and the inside of an Amiga is a reasonably noisy place to try to get 16 bits
of accuracy (an LSB is ~30uV).

So there's a lot more to it than a pair of 16 bit A/Ds.  I'd like to see it too,
but there's a lot to it......
-- 
Fred Hamilton                          "Unlike most of you, 
Harris Semiconductor                    I am not a nut..."
Santa Clara, CA                                            -Homer Simpson