Ring Modulator formulae

[monkeytennis]

Hi. I was wondering whether anyone has a formula for the instantaneous amplitude of a ring modulator's output based on only the instantaneous amplitudes of the two input signals. Is this possible without already knowing the frequencies of the two signals?

The reason I ask is because I am considering writing a program for a PIC which samples two unknown voltages and outputs the correct ring modulated output voltage (or to put it simply, I am considering making a software ring modulator).

Any help would be greatly appreciated.

Cheers,
Simon

 

[mechie]

Ring Modulator in software ?

I suspect this would be a tall order for a PIC at audio frequencies...
the output can't be simply calculated from instantaneous input voltages, you need to find the frequency of every harmonic in both inputs (FFT ?). This will give you two lists of sine wave frequencies, one for input 'A', one for input 'B'
You then need to take each frequency in turn from input 'A' and add it to each frequency from input 'B', then do the same again but subtract, some of these may be negative numbers - so ignore the sign to make them positive.
You now need to simultaneously generate all these sine waves.

I have ignored amplitudes as that would be rwelatively easy after programming the rest but I think the Fourier Transforms would be too much to do in real time , let alone all the other calculations. I have also ignored relative phases, I don't think they would be required.

This procedure would be quite feasable on a modern desk computer - programs like Reason can do it so it is possible.

 

[Nigel Goodwin]

The current issue of EPE has a 'dalek sound effect' using an 18F PIC, it provides a number of different sound effects, but the article says it's not capable of true ring modulation.

 

[mechie]

Dalek voice

I always thought that the Dalek voice was created by 'chopping' the voice by using a square-wave driving the control input on a voltage-controlled-amplifier.
The resultant 'gargling' sound being due to this on/off switching of the voice.

BUT
**broken link removed**
I was wrong again !!!
The BBC use a ring mod !