[PD] types of distortion

Martin Peach martinrp at vax2.concordia.ca
Tue Jul 20 20:25:05 CEST 2004

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.

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