[BC] FM Stereo invention

[padrino]

Group,

What you're talking about is a simple sampling method. Not much different
that what an A/D converter is doing at a base sampling rate. The theory is
the same.

-Frank Foti

Broadcasters' Mailing List <broadcast at radiolists.net> writes:
>In a message dated 02/19/2007 01:58:03 PM Eastern Standard Time, 
>Robertm at broadcast.net writes:
>
>
>> 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.
>
>
>Right, and I have observed exactly this on my oscilloscope. However, the 
>deficiency of the switching menthod becomes immediately apparent when
>there is a 
>large difference between the channels, such as one channel being silent.
>The 
>audio is chopped on/off at 38Khz, at nearly a 50% duty cycle. (Perfect
>switches 
>would make it 50%) That's gotta add distortion along the way. Someone
>else 
>mentioned the harmonics, which can intermod with subcarriers (if present)
>or do 
>other nasty IMD tricks.
>
>
>While the switching method may be *effective*, I don't think it's the
>best 
>way. Someone else pointed out the decoder flaws, and again, those are
>good 
>points... and may, in reality, negate the effects of the "cheaper"
>switching method.
>
>
>Willie...
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