[BC] FM Stereo invention

[Bob Tarsio]

Dave:

It's funny how we all get hung up on specs when in fact the AM stereo
separation specifications were more forgiving than the FM standard and a
well adjusted and maintained AM stereo exciter actually produced good stereo
separation on the order of 15 to 20 dB which is really plenty for the stereo
effect to be noticeable. While we can do a lot with today's technology to go
beyond what the original inventors would have thought possible the effect is
lost mostly on cheap receivers as you mentioned in your post.

I was thinking of another person who should be given some credit for the
practical implementation of a high quality balanced modulator stereo
generator. Albeit indirectly, Barrie Gilbert of Analog Devices who invented
what is known as the Gilbert Cell variable trans conductance amplifier
should be given some recognition. Most all modern integrated circuit 4
quadrant multipliers which are the heart of the balanced modulators used by
many designers used the Gilbert cell technique. Widely used in analog
function modules, arithmetic circuits and yes, audio processors the 4
quadrant multiplier is a great little circuit. I built stereo generators
around these as well as using them as variable resistors in processing
circuits. They are still fun to play with even though better results are
typically gotten with DSP technologies.

It's still fun to roll your own circuits!

Regards,

Bob