[BC] FM Stereo Matrix & TDM

[DHultsman5@aol.com]

In a message dated 2/19/2007 2:15:14 PM Central Standard Time,  
Robertm at broadcast.net writes:

At the  end of the day i think once a filter is designed, the 
switching approach  would be better.  We are really having a historical 
discussion as the  switching method was greatly improved by several 
developers and the matrix  when done completely in the digital domain can 
be virtually  perfect.

R



*****************************************************
 
Robert is correct,  as usual.
 
TDM type stereo generators early on offered advantages both a tube-type and  
solid-state stereo generators.  Most of the early martix type atereo  
generators were tube type.  In an audio matrix L+R / L-R system, the  amplititude and 
phase changes can have severe effects on the performance of the  stereo 
generator.   Later model transistorized "Matrix type" stereo  generators had 
separation similiar to the the TDM type.   I believe  the Gates TE-1 stereo generator 
was a solid state "matrix type".
 
Incidently,  I heard from one of my early mentors in the FM stereo  business, 
that the reason the 29.7 dB. figure was used for an FM stereo  specification, 
was that it was about as good as you could measure graphically  using the 
gratical on the oscilloscope.    This was well before  there were monitors 
available.
 
>From experience with and without a stereo monitor,   It was  difficult to 
meet the separation specification using a major  manufacturer's  tube type matrix 
stereo generator 50 Hz. - 15  kHz..   Another station in town with a 
tube-type TDM stereo generator  was nearly 40 dB without any adjustments.
 
Dave
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