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In the Forum: Off Air Audio
In the Thread: The FM Stereo and Multiplex MPX decoders
Post Subject: Many stereo extraction methods…Posted by Romy the Cat on: 5/4/2008
 peter foster wrote: |
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Thanks Peter.
Yep, the decoder in there is a regular switching type. It is very interesting that the guy state in his comment:
“The sound quality does not change when switching from stereo FM to mono FM except that the the stereo signal
gives good stereo imaging…”
I wonder what happen to noise level. Dima spent a lot of time to explain to me some very rudimental mathematics of stereo extraction in FM. He described many topologies and sub- topologies how it might be done and insist that from mathematics point of view the stereo quality and noise live for ether multiplex method should produce identical result. He also enplaned why increase signal to noise ratio in FM stereo is built within the FM principle. However, he feels that implementation of the stereo decoding still have impact to the amount and quality of the noise. That is why I wonder…
Anyhow, here are a few useful pointers. Our Sansui TU-X1 uses Phase Locked Loop decoder made around the HA-11223W chip. This is archaic chip and there are many contemporary substitutes. I presume that they all sound different. I have no idea what it good or bad but I like how the TU-X1 sounds. So I presume that it is a good sounding chip. Here is a rare datasheet for this chip that hive a very good picture how it works.
http://www.goodsoundclub.com/pdf/MultiplexDecoder11223W.pdf
The switching stereo decoder, as described in the link you provided, it very well explained in the following link:
http://www.goodsoundclub.com/pdf/EicoMX99.pdf
I do have a classic switching Multiplex decoder made by Ampex that uses 4x12AX7 (8 halves) and I am trying to figure out what of produce more interning result. Still, I would like to learn if (regardless of the implantation that I happened to use) one or another topology of stereo extraction is more promising. I even thought to record the full bandwidth along with the 19kHz pilot and with the up to 70 Ha side-band and then to do stereo decoding at digital level, similar to the way how the Accuphase T-1000 does. There are some technical cones and pros in this way. I did not have T-1000 and I heard 3 absolutely contradictive feedbacks from T1000 owners.
http://www.accuphase.com/model/t-1000.html
Anyhow, the digital stereo extraction is also might be considered…
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