The fact, that we can only reproduce frequencies up to half of
sampling frequency, has already been dealt with since the first patch
I posted (2006-01-18).
I chose to use a sample rate of 32000 Hz, which should be sufficient
for our purpose. So we can handle PIT count values down to 75.
Previous patches also played the highest possible frequency for PIT
count values 1-74. I changed this with the square wave patch: It
plays "silence" for frequencies above 16 kHz now.
Currently, I want to keep things as simple as possible. I see no need
for producing more overhead to emulate low-pass filtering for plain
tone generation. We can implement this, when we have realtime PIT
emulation, which would make full PC speaker emulation possible. But,
as you told, there are different kinds of PC speakers anyway.
I'm currently improving the patch a bit and will post one, that could
be included into CVS, soon.
Sebastian Kaliszewski wrote:
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).
--
Joachim Henke
http://he-jo.net/
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