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.
pix.
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.