Hi Bob, Let me just touch on a couple of your points. First:
"... For instance, how does a customer tie a bunch of radios, some running flat and some running pre-emphasized, into one big controller? ... The solution seems to be to run flat audio within the controller, ..." I couldn't agree more. Coming from the commercial two-way world, this is how we do everything, but I do understand why some repeater builders want to go the other way. I just wouldn't call it "flat audio" - it's just normal audio - hook a transmission test set up to it and it sounds normal. Second: "...And the human voice has a natural -6 dB/octave rolloff, which means that ultimately all the audio gets clipped pretty much the same. No dispute there either. That fact is why a repeater can sound similar to simplex. However, when you put a link in the system so that your audio has one more pre-de-emphasis cycle to go through - now you DO have a concern. The cascaded affect of the high end roll off will cause your audio to be degraded. Sequence through two or more links and you have real issues. That's why the big linked systems use flat audio links. Which brings us back where we started - a discussion of the term flat audio. In the commercial world there is nothing confusing here. In Motorola terms, when an exciter is configured for flat audio it does not use pre-emphasis. When a receiver is configured for flat audio it does not use de-emphasis. A flat audio link is simply a point to point communication channel configured using a transmiter that has no pre-emphasis and a receiver that has no de- emphasis. Other than the case of a link, in commercial systems, the term flat audio never comes up. However, when an amateur repeater is said to be a "flat audio" repeater, it seem logical to conclude that the repeater's receiver does not use de-emphasis and the associated repeater transmitter does not use pre-emphasis. Naturally, this means that the audio between these two devices is not "normal". It has the initiating user's pre-emphasis. It is somewhat like dealing with terms in four-wire audio circuits. These have "transmit" audio and "receive" audio where the terms in fact relate to directions that audio is moving at a particular interface rather than a direct relationship to a system transmitter or receiver. Being able to keep all these confusing terms straight is why we get the big $ in the radio business. [Ha.] 73, nj
