On Mon Jul 24, 2006 at 06:18:30PM +0200, oliver wrote:

hi, list

maybe someone here on the list has done this before...

i'm looking for an "easy" way to distort audio the same way a bad FM or AM receiver does. i don't just want to crossfade the original audio with some random noise, but i want the actual interference-results i get when the dial of a radio station gets slightly out of signal.

sure. i think to do it optimally you need more bandwidth than 44100 though. especially since radios can get interference from the superheterodyne frequency (eg 21.7 Mhz above or below the current), harmonics on a 1200khz channel from a 600Khz or 1Mhz channel etc.

im AM youll often get the effects of a dozen distant carriers on almost the same frequency, plus the 10khz whine from the next channel (9khz in europe).

is the "Frequency Modulation" used in music synthesis exactly the same as the one used in the FM radio bands? i still think youd need some noise, eg to modulate the strentch of the 'weaker' signal so that it occasionally locks onto it in favor of the closer signal, for interference purposes

im also interested in what you find out about the phase distortion that happens with weaker FM signals. ive foudn if you mono-up all the spectral content above 10khz or so, you can remove the static of a weak stereo signal but retain most of the seperation (since lower freqs carry more energy)..

oliver wrote:

hi, list

maybe someone here on the list has done this before...

i'm looking for an "easy" way to distort audio the same way a bad FM or AM receiver does. i don't just want to crossfade the original audio with some random noise, but i want the actual interference-results i get when the dial of a radio station gets slightly out of signal.

anybody knows how to do this ?

For AM, it's like ring-modulation: you multiply the signal with the output of an [osc~] whose frequency is proportional to how out of tune the radio is. To me FM just sounds noisier when it's off-station. (the effect should be to add a DC offset to the sound, thereby limiting the dynamic range) I would maybe clip the signal according to the amount of detuning and add/multiply some low-frequency noise. Then add some noise bursts from the nearby electrical equipment and thunderstorms...

Martin

thanks for any hints on that matter

oliver