[BC] FM Stereo invention

[Robert Meuser]

Willie:

Look at it in these terms. In a switching system where the left and 
right channels are sampled at 38 kHz, if the signal is pure mono the 
left and right channels are identical and there is no switching 
component in a perfect world of zero rise time switches. If there is a 
difference between left and right, then that difference appears as alias 
of 38 kHz which is the sum and difference of the baseband frequences and 
38 kHz. In other words a 38 kHz DSB signal. That is what makes the 
switching and matrix system mathematically equivalent.

R


WFIFeng at aol.com wrote:

>In a message dated 02/19/2007 12:15:10 PM Eastern Standard Time, 
>mark3xy at gmail.com writes:
>
>  
>
>>As most of you know, the FCC-approved stereo FM system was jointly
>> developed by GE and Zenith.  The difference was that Dr. Adler of
>> Zenith viewed it as a time-division-multiplex scheme (L and R
>> alternately sampled at a 38 kHz rate) while Tony Csicsatka at GE used
>> a matrix and balanced modulator to generate the L-R subcarrier.
>> 
>> He was undoubtedly a brilliant engineer.
>>    
>>
>
>The interesting thing is that both of these methods generate virtually the 
>same result! Some of those FM stereo generators on-a-chip use analog switches at 
>38Khz to chop the L and R signals alternately. The end result is a "standard" 
>stereo signal. Pretty slick "shortcut".
>
>Willie...
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