[PD] types of distortion

pix pix at test.at
Tue Jul 20 20:45:42 CEST 2004

ah i had the feeling when i mentioned AM that it would be a very
uninsteresting case. FM seems to generate all sorts of odd distortions
when you are off signal though. i figure it would be hard to model
exactly in realtime since the carrier signals are so high, but a similar
summary of the audible effects would be useful. 


On Tue, Jul 20, 2004 at 02:25:05PM -0400, Martin Peach wrote:
> pix wrote:
> >... if anyone knows of a good description of all of the different
> >distortions that come into play when an FM or AM radio signal is poorly
> >recieved, please fill me in.
> > 
> >
> In AM the radio-frequency sine wave is Amplitude Modulated by the 
> signal. In the receiver if the local oscillator is not running at the 
> same frequency as the transmitter sine wave, you get sidebands in the 
> signal whose frequency is the difference between the remote and local 
> oscillators plus the frequency of the signal. This can be simulated in 
> pd by multiplying [*~] two signals together, one of which is a sine wave 
> [osc~], and the other is up to you. All the other distortions in radio 
> are mostly noise, a constant background with bursts from lightning and 
> motors. Whistlers are caused by lightning impulses bouncing around in 
> the earth's magnetic field: different frequencies travel at different 
> speeds, so the original click is smeared into a descending chirp of noise.
> .
> Martin.

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