[EMAIL PROTECTED] wrote: > So that's one vote for running pre-emphasized audio throughout the > controller. > > To do that, all receivers must provide discriminator audio, and the > controller's internal tone generation and digital audio playback must > have pre-emphasis. The DTMF decoders must have de-emphasis. Any > autopatch would need de-emphasis on the outgoing audio and pre-emphasis > on the incoming audio. Am I missing anything?
Yes, internal transmitter processing. Consider the AP-50, please. It is 'programmable' as to what type of audio feeds the processor, and what type of audio feeds the transmitter, using jumpers. Since there is nothing inherently evil about de or pre emphasis, why MUST we build a controller that has to deal with pre-emphasized audio? I think we simply need to ensure that our controllers audio path is good from 50 to 5000 cycles (most aren't and that's where the problem lies). Design the receiver de-emphasis so the knee is at 50 cycles (YES 50 Hz, you listening CAT ?) Then, ensure the upper edge of the audio spectrum is at at least 5000 Hz. With modern high slew rate op-amps, this isn't hard to accomplish, just don't use a LM-1458. Depending on the builder, possibly the greatest advantage "flat audio" modification provides is usually a better modulator for the transmitter, and greater conveyed audio bandwidth. In most cases people building flat audio repeaters will convert the pm exciter to true FM and will ensure the audio reaching the transmitter hasn't been high pass filtered to death (somebody say TS-32 HPF) and, isn't low pass filtered to death (they aren't using the original clipper/filter blob in the exciter that may have a high cut off of 2K or slightly more). It's the cascading effects of the filtering that makes links sound bad, not the emphasis stages. Kevin Custer
