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Re: [Qemu-devel] [PATCH] PC speaker emulation (square wave)

From: Sebastian Kaliszewski
Subject: Re: [Qemu-devel] [PATCH] PC speaker emulation (square wave)
Date: Thu, 26 Jan 2006 17:55:40 +0100
User-agent: Mozilla Thunderbird 1.0.2 (X11/20050322)

Joachim Henke wrote:
Ok, I simplified my patch to generate just plain square waves. Indeed, its sound is much closer to a real PC speaker now.

Does "cut off frequency" mean, that we have silence above that specific frequency?

No. Typical cutoff freq is where components of the signal are attenuated by 3dB (i.e. are half as loud). At 2 times taht frequency they'll be attenuated by 3 + A dB, where A is filter's rate in dB/octave. Typical 1st order filter is 6dB/octave, 2nd order is 12dB/octave, etc. Typical soundards used no more than 2nd order filter.

But, if you want to have your path behave really nicely, you should simply not generate at all waves at frequencies above half of current output sampling rate -- those can't be reproducted -- instead significant distortion will be generated (google for Nyquist frequency).

Sebastian Kaliszewski

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