From alsa-devel-owner@alsa.jcu.cz  Mon Jul 27 01:49:13 1998
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Date: Mon, 27 Jul 1998 01:40:40 +0200
From: Marcus Brinkmann <Marcus.Brinkmann@ruhr-uni-bochum.de>
To: alsa-devel@jcu.cz
Subject: Re: Sample rate conversion (was: ALSA driver 0.2.0-pre2)
References: <19980723121606.B1702@ruhr-uni-bochum.de> <199807261004.MAA05890@obelix.fvdpol.inter.nl.net>
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In-Reply-To: <199807261004.MAA05890@obelix.fvdpol.inter.nl.net>; from Frank van de Pol on Sun, Jul 26, 1998 at 12:04:51PM +0200
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On Sun, Jul 26, 1998 at 12:04:51PM +0200, Frank van de Pol wrote:
> Marcus Brinkmann wrote:

> The trick to first resample to a higher frequency and not directly to the
> desired frequency is to allow a simpler filter. In this case a 'not so
> steep' filter (ie. shorter FIR filter) is good enough. 

Cool. Frank, thank you very much for your explanations!

> One big concern:
>
> quality 0: (least)
> 	- simple sample rate conversion, by simply repeating old values.
> 	  will give a 'harsh' sound, with losts of additional frequencies
> 
> quality 1: (better)
> 	- use linear interpolation to get the desired frequency. For most
> 	  applications this does sound quitte good.
> 
> quality 2: (even better)
> 	- linear interpolation, with the over sampling and low-pass
> 	  filtering.

I had this idea... would it be better to disallow resampling to lower
frequencies? Just take the highest frequency rate in a stream and convert
the lower frequencies with quality 0 or 1. Do you need a low pass filter
then? 

Note that I only study math and physics, not signal processing. :)

Marcus

-- 
"Rhubarb is no Egyptian god."        Debian GNU/Linux        finger brinkmd@ 
Marcus Brinkmann                   http://www.debian.org    master.debian.org
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