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Organization: University of Illinois at Chicago
Date: Monday, 24 Jun 1991 21:45:40 CDT
From: Jason Kratz <U28037@uicvm.uic.edu>
Message-ID: <91175.214540U28037@uicvm.uic.edu>
Newsgroups: comp.sys.amiga.audio
Subject: Re: CHEAP 16-bit STEREO sound samplers
References: <17787@chaph.usc.edu> <744@cronos.metaphor.com>
 <8674@jhunix.HCF.JHU.EDU> <91166.165734DXB132@psuvm.psu.edu>
 <282.2865f3ac@intersil.uucp>

In article <282.2865f3ac@intersil.uucp>, hamilton@intersil.uucp says:
>
>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

At least someone agrees with me that a decent 16 bit board wouldn't be so cheap
.  You're correct on every point Fred.

Jason Kratz - U28037@UICVM.CC.UIC.EDU