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

[Sebastian Kaliszewski]

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).

rgds
--
Sebastian Kaliszewski