From alsa-devel-owner@alsa.jcu.cz  Thu Jul 23 12:15:17 1998
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Date: Thu, 23 Jul 1998 12:16:06 +0200
From: Marcus Brinkmann <Marcus.Brinkmann@ruhr-uni-bochum.de>
To: Thomas Sailer <sailer@ife.ee.ethz.ch>
Cc: alsa-devel@jcu.cz
Subject: Re: ALSA driver 0.2.0-pre2
References: <35B303E7.E9ECFBB7@ife.ee.ethz.ch> <Pine.LNX.3.96.980720112358.22254F-100000@entry.jcu.cz> <19980722222258.A3598@ruhr-uni-bochum.de> <35B7003B.211CD8A3@ife.ee.ethz.ch>
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In-Reply-To: <35B7003B.211CD8A3@ife.ee.ethz.ch>; from Thomas Sailer on Thu, Jul 23, 1998 at 11:19:55AM +0200
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On Thu, Jul 23, 1998 at 11:19:55AM +0200, Thomas Sailer wrote:
> 
> Ugh. What you're suggesting is linear interpolation.
> This is indeed used in commercial sample rate converter chips,
> _BUT_ only as a last stage, preceded by a polyphase low pass filter,
> and this is what you have to do if you want decent quality.
> Just using linear interpolation gives you significant new (and thus
> unwanted) spectral components.

Okay, I see everyone else than me knows better about this. :) Thank you for
your explanation, it is very much appreciated. I think the low pass is used
to filter out the high frequencies that can't be presented in the new sample
rate? How are pass filteers implemented in software (do you need Fourier for
this, this would be slow...)?

Thank you,
Marcus

-- 
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