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Subject: Re: DSP: low pass filter

Re: DSP: low pass filter

From: Dave Hooper <>
Date: 2005-08-14

Hold on, hold on. A low-pass filter is WAY easier than an FFT - FFT is
overkill for beat detection. Check out implementations of Butterworth FIR
filters, or even just hack something together by averaging a bunch of
samples together: at 44.1kHz, if you average 128 samples at a time, you
have a rough-and-ready 180Hz filter.

The existing peakmeter code looks at peaks over a frame-worth of samples -
you just change that so that it builds an average every 128 samples, and
then looks at peaks across all of those averages.
Should be a piece of cake.

----- Original Message -----
From: "Magnus Holmgren" <>
To: "Rockbox development" <>
Sent: Sunday, August 14, 2005 4:55 PM
Subject: Re: DSP: low pass filter

> Tomas wrote:
>> Ok, then the next problem is... how to make a lowpass filter if I have an
>> FFT? (I've found some other FFT sources too)
> What you get out of an FFT is a set of amplitudes for a set of equal-sized
> frequency ranges. So just check the right bunch of amplitudes. Wikipedia
> should explain the basics...
> Magnus
> _______________________________________________

Received on Sun Aug 14 22:28:21 2005

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