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From: bowers@elxsi.dfrf.nasa.gov (Al Bowers)
Newsgroups: sci.electronics,comp.std.internat,rec.video,comp.graphics
Subject: Re: I don't need HDTV!
Message-ID: <BOWERS.90Mar21114921@drynix.dfrf.nasa.gov>
Date: 21 Mar 90 19:49:21 GMT
References: <sa0KhqO00Uh7M2R25C@andrew.cmu.edu> <5478@okstate.UUCP>
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Organization: NASA Dryden, Edwards, Cal.
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In-reply-to: minich@a.cs.okstate.edu's message of 20 Mar 90 18:52:05 GMT

In article <5478@okstate.UUCP> minich@a.cs.okstate.edu (MINICH ROBERT JOHN) writes:

>From article <sa0KhqO00Uh7M2R25C@andrew.cmu.edu>, by bas+@andrew.cmu.edu (Bruce Sherwood):
>> The analogy with audio is that a CD with frequency response out to 10
>> MHz would not sound better than one with frequency response out to 20
>> KHz, because the human ear can't hear the higher frequencies.

>  Well, it probably would sound a bit better. Consider this:

>A 20KHz sample on CD looks something like this


> * * * * * * * * * *
>* * * * * * * * * *

Exactly!  Or maybe I would have described it as:
_ _ _ _ _ _ _ _ _ _ _
 _ _ _ _ _ _ _ _ _ _ 

>which is just a dumb square wave. Sure, it's at high enough of a pitch 
>that most people wouldn't be able to discriminate between it and a pure sine 
>of the same requency, but what happens if, say, you have a 20,001Hz waveform? 
>Then, 20KHz just isn't enough to provide a nice, "symetric" waveform. Thus, 
>you get a somewhat harsh sound. If I were really after "human limits" sample,
>I'd bump the rate up to around 30KHz to minimize the distortion.(Assuming that
>a 40KHz sample is "wasteful".)

I realize that this is a little out of place but as an example we in
the aircraft industry prefer to sample at a minimum of 5 times the
maximum frequency of interest and we usually prefer 10 times the max
frequency.  Now I realize that this is far and away more than required
for decent sound (or maybe even exceptional sound) but having the cut
off just above the limit of average human hearing just seems to be a
little rash.

--
Albion H. Bowers  bowers@elxsi.dfrf.nasa.gov  ames!elxsi.dfrf.nasa.gov!bowers
         NASA Ames-Dryden Flight Research Facility, Edwards, CA
                  Aerodynamics: The ONLY way to fly!

                     Live to ski, ski to live...