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Originally Posted by altis
I've found some pictures of the back of some analogue boxes that have stereo audio outputs. Reading some of the words that go with them makes me suspect that they actually use the 88-108 MHz FM radio service for this. These boxes possibly predate Nicam too. This also explains why I can listen to Sky 1 using the FM hook-up!
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Thats interesting, (can you pm me some links) cos to be of any real practical use the box would have to contain either a nicam decoder or an FM tuner which would have made it a very expensive box for the cable operator.
The mechanics of FM hook ups are different from site to site but generally, the audio is taken from the sat receiver into a multiple output amp, one o/p of which is fed into a nicam encoder (which also provides the mono) and into the modulator for transmission over the network, while a second o/p is fed into an FM processor and then sent out over the network as an FM carrier to be picked up by an FM tuner with a 75 ohm input.
These are referred to as simulcast FM's as opposed to the FM radio stations which are also carried in some areas. The idea behind them was that it would be a good selling point in the early 90's when the cost of Nicam TV's was still beyond the means of the majority of households.
Anyway though to get back on topic
I have heard that some of the GI/Jerrold boxes have a mono audio output, (pretty pointless if you ask me but no doubt another gimmick pushed by some marketing exec) which is probably what Reaps^ is using. Afaik beyond demodulation to baseband there is no other processing of the audio before it goes to the mono o/p socket and the TV. I'm not sure if the splitting takes place before or after volume control though.
Its difficult to make a call as to what this problem is but the best bet is to give faults a ring and get a service tech out to have a look, as it's more likely to be an ntl issue than something that you can sort yourself Reaps^
edited for spellink 
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