[sdiy] What is a quadrature oscillator good for?

[Andre Majorel]

On 2003-09-08 10:13 -0500, Cornutt, David K wrote:

> From: Grant Richter [mailto:grichter at asapnet.net]
>
> > Aside from frequency shifters and qudraphonic panning, is 
> > there anything else a quadrature oscillator is good for?
> 
> There's a modulation technique used in satellite radio
> known as quadrature phase shift keying, or QPSK for short.
> I'll have to admit I don't fully understand it, but basically
> the idea is that you shift the phase of a carrier signal
> to one of the four polar quadrants (0/90/180/270 degrees)
> to represent one of four states that you want to transmit.
> (For instance, each transition might represent two bits
> of binary data.)  For a while now I've wondered what that
> would actually sound like if it were done at audio frequencies,
> and what the synth possibilities might be.

Would that be FM or AM ? Is the switch instantaneous, and how
often does it occur ?

-- 
André Majorel <amajorel at teaser.fr>
http://www.teaser.fr/~amajorel/