Rockbox mail archive
Subject: Re: DSP: low pass filterRe: DSP: low pass filter
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From: [IDC]Dragon <idc-dragon_at_gmx.de>
Date: Mon, 15 Aug 2005 21:21:10 +0200 (MEST)
> Thanks, we got to the point that averaging is enough on IRC tonight
> too... but we had no way to calculate how many samples to average...
I suggest using an IIR filter instead of FIR. You need way less past samples
for each step. The most simple IIR filter is like a charge/discharge (first
order lowpass): e.g. take 90% of your "charge", 10% of the new value, to get
the new charge. Play with the parameters, generalized it's n and (1-n). If
you use less of the current, the thing becomes slower, lower corner
frequency.
Power of two gives the benefit of using shift instead of multiply. Use >16
bit for the charge.
Jörg
Date: Mon, 15 Aug 2005 21:21:10 +0200 (MEST)
> Thanks, we got to the point that averaging is enough on IRC tonight
> too... but we had no way to calculate how many samples to average...
I suggest using an IIR filter instead of FIR. You need way less past samples
for each step. The most simple IIR filter is like a charge/discharge (first
order lowpass): e.g. take 90% of your "charge", 10% of the new value, to get
the new charge. Play with the parameters, generalized it's n and (1-n). If
you use less of the current, the thing becomes slower, lower corner
frequency.
Power of two gives the benefit of using shift instead of multiply. Use >16
bit for the charge.
Jörg
-- GMX DSL = Maximale Leistung zum minimalen Preis! 2000 MB nur 2,99, Flatrate ab 4,99 Euro/Monat: http://www.gmx.net/de/go/dsl _______________________________________________ http://cool.haxx.se/mailman/listinfo/rockboxReceived on 2005-08-15
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