[BC] FM Stereo invention

[DHultsman5@aol.com]

In a message dated 2/19/2007 12:57:56 PM Central Standard Time,  
Bob at Broadcast-Devices.com writes:

The  mathematics of stereo wave modulation can be applied to both methods  and
the result is the same. I don't think that with today's components  there is
a real difference in performance between the two methods. The  balanced
modulator method provides excellent results without the need for  the alias
filtering at the output that switching modulators require. Phase  linear
filters were difficult to synthesize back in the early 60s which is  what
made the balanced modulator method novel. Today phase linear filters  to do
the job are available in integrated circuit form for a couple of  bucks. I
honestly think that most of the deficiencies in stereo mod/demod  occur in
the receiver. Cheap demodulator circuits often provide adequate  results but
fail to provide what was available at the transmitter. On the  transmit side,
matrix 


******************************************************************
 
Bob:
 
 
Basically you hit the nail on the head.   Many were surprised at  the idea of 
a stereo specification that was less than 30 dB  Separation.    However most 
of those were comparing the crosstalk  from stereo two-track tapes,  which was 
much better.   However  the the separation on the stereo discs 45/45 was 
usually less than 30 dB until  better cartridge and stylus development came along.
 
The larger problem for many years was the specifications on the FM Stereo  
receivers.  The receiver/decoders both tube and solid state in the first 10  
years from 1961 thru 1971 got better each year.  We tested alot of early  tube 
type receivers from Fisher, Scott and other manufacturers and their  separation 
was usually better than 30 dB.  Many of the cheaper lines seldom  decoded any 
better than 20-25 dB or even less. 
 
There were some stereo receivers that basically I think had two amplifiers  
and a 19 kHz. decoder to lite the stereo lite and some audio filtering to make  
the left and right channels sound different.. They may have been mono.
 
I remember when we replaced a medium priced stereo tuner used in our  studios 
for an air monitor with a stereo modulation monitor and the jocks loved  the 
great separation.
 
Dave
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