This is getting slightly off the original topic... I suppose some mild amount of equalization can help, but it can also be implemented completely incorrectly and cause a lot more harm than good.
Case in point (Dave M, start laughing) is a local UHF repeater. The trustee has a slight hearing problem (loss of high-freq) and almost all of the users have Yahoo handhelds (VX2s, etc). Naturally there's an EchoLink port and multiple receivers, and links to just about everything in the area. The main repeater has had its pre-emphasis, audio filtering, and limiting defeated and a stereo EQ feeds it. Basically it is a straight line from -20dB at the low end (20Hz) to +20dB at the high end (20kHz) using both channels in series, way more than the standard 6dB/octave pre-emphasis, and no low-pass cutoff above 3 kHz. No test equipment was used to set up levels; it was all done by ear in an attempt to get FM broadcast-quality audio out of a 1 inch speaker. So with no limiting or low-pass filtering, the repeater puts out strong sidebands up to 20 kHz away, pretty much ruining any use of another repeater that's the reverse split, 25 kHz adjacent, and 13 miles away. A deviation scope shows peaks out to 7 kHz, but a spectrum analyzer shows a much wider bandwidth, almost all of which is high-frequency noise from marginally weak signals that gets amplified way out of proportion to the actual voice audio. So if you must use an EQ, make sure the transmitter still has the final word on pre-emphasis, low-pass filtering, and limiting. Bob M. ====== --- On Fri, 9/12/08, ldgelectronics <[EMAIL PROTECTED]> wrote: > From: ldgelectronics <[EMAIL PROTECTED]> > Subject: [Repeater-Builder] Re: Comspec TS32P encoder control (CAT Audio) > To: [email protected] > Date: Friday, September 12, 2008, 1:22 AM > Mike, > > I have the same general question about repeater audio. What > does it > really supposed to sound like? In my systems, I try to make > it so the > repeater output sounds like the repeater input. In other > words, it's > close what you would hear if you were simplex. For me, it > doesn't > sound like CAT or Arcom. I'm sure that others have > their favorite way > to make their repeater sound (a little compression may also > sound good). > > The repeaters that I have are mixed with Arcom and CAT > controllers. In > general, I like the sound of the (non-modified) Arcom > better, but that > is just me and it's not by a great amount. We have some > users that > like the CAT sound and some that like the Arcom. > > If you have a CAT controller that sounds bad, then there > may be an > impedance mis-match or you have the de-emphasis jumper in > the wrong place. > > A couple of the CAT systems have a rack mounted 15 band > stereo EQ in > line with the receiver. The controller enclosure got RCA > jacks mounted > on the back (or side) and there is a 3 foot RCA cable > between the > controller and EQ. In this case, it worked out very well as > the > systems have a link receiver on it that also needed some > audio shaping. > > The EQ can then be used to shape the audio any way you > like. For this > system, I went right in between the normal CAT sound (less > highs) and > the normal Arcom sound (a little brighter) to get what I > perceived to > be a "simplex" sound. > > Your mileage (or sound) may vary. > > Dwayne Kincaid > WD8OYG > > > > > > Hmmm . interesting comment Bob. What IS a repeater > supposed to > sound like? > > Having a CAT controller I can tell you I HATE the > audio. ..stinks. A > > cheaper ARCOM on the same repeater sounds far better. > This sounds to me > > like personal preference. But as this is THE > BUILDER"S forum, has > anyone got > > some ideas on how to improve the CAT audio other than > to replace it? > - Mike
