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From: jbuck@galileo.berkeley.edu (Joe Buck)
Newsgroups: sci.electronics,comp.dsp
Subject: Re: A question about the Nyquist theorm
Message-ID: <11542@pasteur.Berkeley.EDU>
Date: 28 Feb 91 23:31:21 GMT
References: <20408@shlump.nac.dec.com> <625@ctycal.UUCP> <11515@pasteur.Berkeley.EDU> <1991Feb28.084837.7506@appmag.com>
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Reply-To: jbuck@galileo.berkeley.edu (Joe Buck)
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In article <1991Feb28.084837.7506@appmag.com>, todd@appmag.com (Todd Day) writes:
|> Not all CD players just insert zeroes.  I used the same double oversampling
|> chip and the same DAC as my Denon 1500 CD player (well, I used the serial
|> versions) in my 56000 project board.  The oversampling chip did do
|> interpolation (and it was slightly more complex than bilinear (cubic spline?
|> I don't remember)).
|> 
|> I know the math works for inserting zeroes if you use a sinc function to
|> reconstruct the signal.  However, how does it work out for reconstruction
|> with a near step function?  I've never run through the math on that one...
|> Quickly off the top of my head, it doesn't look like it will work...

If a step-function is used, then you get a sinc function in the frequency
domain.  What happens is that you have a rolloff at high frequencies (that
is, this introduces a distortion).  Some manufacturers use this anyway, and
then add another filter to boost the high frequencies by a corresponding
amount to compensate for this distortion.

--
Joe Buck
jbuck@galileo.berkeley.edu	 {uunet,ucbvax}!galileo.berkeley.edu!jbuck