From: amiga@uhunix2.uhcc.Hawaii.Edu (ftp Amiga Manager)
Subject: Re: Amiga 4000 & HYPE! -Reply to Jerry Shekkel
Organization: University of Hawaii
Date: Tue, 29 Sep 1992 22:00:22 GMT

In article <1992Sep28.182632.9432@sol.ctr.columbia.edu> jerry@connection.prospect.com (Jerry Shekhel) writes:
>04@eng2.eng.monash.edu.au>
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>10667547@eng2.eng.monash.edu.au (JIMMY FANG) writes:
>>
>>Frequency Modulated sythesized sound on the PC would be more analogous to 
>>telephone quality.  Digital sound is more akin to CD quality and FM is to 
>>AM transitor radios.
>>
>
>I think you're either confused, or your hearing is seriously different from
>mine.  On my sound card (PAS-16), FM music is *crystal clear*, clearer than
>any telephone transmission or radio I've ever heard.  Of course, it doesn't
>sound like it's being played by real musical instruments, but that's
>understandable given that it's synthesized and not digitized.
>
>Digitized music *does* sound like it's being played by real musical
>instruments, but its quality (clarity and richness) depends heavily
>upon several things, such as frequency and sample resolution.  CD's play 
>16-bit 44.1KHz stereo music.  MODs utilize only 8-bit samples, and the
>frequency is what, 22.1KHz?  This is *not* CD quality, even if we ignore the
>fact that MODs are compressed, sampling only one note per instrument.
>

Maybe I am misunderstanding what you were trying to say here, but I think you 
may both be a little confused.  The quality of digitized audio does depend 
heavily on several things, such as frequency and sample resolution, but not 
quite in the manner that's been explained so far.  When you digitize analog 
data, you have to basically do two things: sample it and quantize it.  The
sampling theorem tells us that to completely and accurately reproduce a 
signal bandlimited to frequency f, you have to sample it at least 2*f samples
per second.  Sampling at less than this rate will result in aliasing
distortion.  Audio CD's are bandlimited to 20,050 Hz (the typical range of
human hearing is what, something like 15 - 15,000 Hz for the average adult?)
and thus you need to to sample the audio data at 44,100 samples/second.
The highest frequency that can be recovered is still 22,050 Hz though.  The
CD's 16 bits are for quantization and gives, ummm, 2^16 = 65536 quantization
levels.  Depending on the type of data being digitized, there are different
quantization schemes (linear, delta, exponential, etc.) which may be
appropriate.  Maybe this is where I may be misinterpreting your response
above.  If you meant that MOD's only sample at 22,100 samples/second with
8 bits of quantization, then the highest frequency they would be capable of 
reproducing would be ~10KHz, then you would be right -- this is not CD
quality.  If you meant that the frequency repsonse of a MOD is 22.1KHz, then
this is pretty much equivalent to a CD, athough you wouln't have as many 
quantization levels available, but a well chosen quantization scheme may
help here.  Telephone audio sounds bad, even when digitized because it is
bandlimited to ~3KHz.  This is ok for speech, but not something with and
extended frequency range like music.  I'll stay out of the rest of this
MOD/SoundBlaster/whatever debate 'cuz I know next to nuthin' 'bout them
things.  Feel free to correct any of my own goofs above...

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