From: Paul Khoury (pkhoury_at_loop.com)
Date: Tue Feb 10 1998 - 00:59:15 EST
On Mon, 09 Feb 1998 17:06:15 -0700 (MST), billy_at_MIX.COM wrote:
>> >22kHz is a bit high for a 44.1kHz sampling rate - the high frequency
>> >limit is one half the sampling rate...
>> >
>> I don't quite understand (for a change. <g> ). Could you explain that
>> again, please?
>
>In the world of digital sound recording and transmission there is
>what's called (I believe) Shannon's law (many years since I was in
>school) which says the highest frequency that can be digitized is
>one-half the digital sampling rate. Thus a 44.1kHz sample rate
>system can only go up to 22.05kHz. Then there are anti-aliasing
>low-pass filters to enforce this, but they are not perfect so there's
>some gradual decline in frequency response before hitting the actual
>cutoff point. Since in this case you are only 50Hz away in practice
>there will not be much left of your signal after going through this
>filter.
>
>For what it's worth any decent analog tape recorder running at
>15 ips (inches per second) or faster would record this quite well.
>Or if you could sample at 48kHz you might have a chance of getting
>it that way too. I don't know what software might be available
>for the Thinkpad at that sample rate though.
>
>The next step in commercial systems looks like a 96kHz sample
>rate - if this eventually finds its way into notebook computers
>you'd have no trouble at all, but that's probably a year or
>two away.
>
I'm just trying to record a train passing by for a small project,
so if I choose 22KHz, is that the sample rate, or the other rate?
Or do you think 11KHz might work fine as well?
-- Paul Khoury pkhoury_at_loop.com http://pkhoury.dyn.ml.org (if you can't get to the website, then I'm not online)To request a list of available docuements, reply with DOCUMENTS in the subject line.
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