On Sep 11, 2008, at 11:22 PM, ldgelectronics wrote: > 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.
This is definitely a "religious" debate amongst folks. Some people like to have "what comes in is what goes out". Others like to "process" the audio and try to enhance (to their ears) speech intelligibility, or lower noise, or whatever they personally like. Many modern commercial repeaters do some "processing" of the audio out of the box, and you can't really stop them. (Kenwood, I'm looking at you. Motorola too, but it's kinda expected from them now that they've been doing it for years.) I'm in the "what goes in is what goes out" camp. I figure it this way... People are responsible for their own "signature" on-air sound. If they take the time to have a good sounding signal, they sound good through the repeater. If they have a tinny, nasty, underdeviated, whatever... signal... that's how they sound through the repeater. Overdeviated is a different beast, since our repeaters are coordinated for not only a specific frequency, but also a bandwidth, so to speak. Thus, a limiter that either cuts them off completely or keeps them within the confines of the repeater's coordinated deviation limits, is required. That's the only time we "do anything" to their signal and we use the factory limiter circuit in the MASTR II.) Comments about CAT and Arcom: I haven't really heard too many of either on-air around here (or I can't tell), and the few that are around that I know for sure are CAT or Arcom, I'm usually working them from far enough away that I can't really listen to other users on the input to make a fair comparison/analysis. Plus I can't really tell if it's the controller, or a poor/different choice of radio for receiver/ transmitter that's causing the differences. If I had to be pressed to say what I think of them, I'd say the CATs sound kinda "bassy" to me, but I'm not sure if it's the CATs doing that, or something else in their systems is set up wrong. Or maybe their repeater tech likes it sounding that way. > 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. This is often true of ANY controller. LOTS of people hose this up in IRLP too. IRLP's network standard is DE-emphasized audio... some people put the discriminator of their rigs straight into the sound card and send it to the rest of us. Yuck, tinny, nasty... gross. (And incorrect for the network standards.) > 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. I'm just personally "not into" this, but if it works for you... cool with me. I can't say much, one of our links sounds like CRAP and I've had the gear in the hands of someone else who's "working on it" to replace the link with a VoIP link, and it's just not going anywhere. He'll get around to it eventually and the link has sounded bad for years now... (sigh)... luckily it's not used too much. It used to be linked via user-command and I made the "executive decision" that we'd switch it to full-time linked with a command to turn it OFF for a while if someone needed the other repeater... that turned out long-term to be a huge mistake, since it highlighted how bad it sounds. Sigh... > 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. Hmm. See notes below on what I'm expecting a controller to do to audio... (nothing). > Your mileage (or sound) may vary. What I *like* to do is not what I usually have TIME to do, but on the couple of MASTR II setups I've had time to work on, I've SWEPT them. I set them up using the usual 1000 Hz tone at 3.0 or maybe 3.5 Khz deviation on the receiver input, get that EXACTLY right on the output, and then change to lower and higher tones, and make a quick Excel or graph-paper graph of any changes in level... and see if the darn thing is really flat response. What goes in, is what comes out. Down way down low, the filters for the CTCSS tone on the TS-64 or the factory MASTR II boards starts to get in the way, and you can plot their curve if you have enough test points, but... here's the real deal, for me anyway... I'm one SPOILED guy. See I'm fairly young and took to repeater work quite a while after I became a ham. The clubs and groups I got involved with ALL run S-Com controllers. And (not kidding here now...) I have yet to find an S-Com/MASTR II that someone else built in these networks and repeaters that isn't so close to flat, you can't really tell the difference. (I'll preface that with saying that's IF you follow S-Com's procedure in their documentation for setting levels INSIDE the controller to the voltages they recommend AND the MASTR II is tuned/performing to factory spec.) Once you get used to hearing machines that just repeat what they hear... you like it. We're not as "nuts" about so-called "flat audio" as some groups installing direct discriminator to exciter turn-arounds with hard- limiters in them, but most folks are hard pressed to tell the difference between a user on the input and the repeater output on our S-Com equipped MASTR II repeaters. We feed Vol/Sq Hi into the S-Com's with the de-emphasis capacitor recommended by them added at the receiver input inside the 7K... the audio "inside" the controller is de-emphasized "normal" audio... and then back out into the normal audio inputs of the MASTR II... none of the "flat-audio" stuff that some larger west coast and other groups have done. Search the list archives for "flat-audio" to see some AMAZINGLY good engineering discussions about how to accomplish a REAL what-goes-in-is-what-comes-out setup... over multiple hops. Out here, so far we're just not that picky. But we understand why LARGE linked systems do it... they're fighting that little bit of audio quality loss at each "hop" in the linked system... and they HAVE to get ultra-aggressive about not lowering audio quality by even a TINY bit at each hop, or by the time you're five hops away in links, it starts to sound bad. Guess which of our links sounds bad... (and it doesn't have S-Com's on it, nor is it built out of MASTR II's...)... the multi-hop one. The other link -- the one that's a MASTR II user repeater, to S-Com 7K, to MASTR II repeater (upside-down linking pair) to MASTR II repeater (right-side up linking pair) to S-Com 7K to MASTR II user repeater... once all the levels were set right... it is VERY HARD to tell if someone's on the other end, unless you listen to our subtle courtesy beep tone change that indicates the last receiver active was the LINK, and not the main receiver. If you're really picky you can hear TINY timing differences on the unkey too, since we're using STE on the link to close the receivers cleanly. There is ONE downside, a human one, to having "near-perfect" sounding links. The guy that pops up and says, "How do I get to Interstate 25?" Well... first you have to tell me what CITY you're in, and if neither that guy or the guy answering him even REALIZES they're on a linked system, hilarity ensues until someone comes on the air and sorts it out for them, and explains that one guy is in City X, and the other is in City Y. Having a little bit "dirtier" link SOMETIMES is a reminder to people that the person is SOMEWHERE ELSE that they're talking to... but in all honesty, I've heard IRLP systems linked into IRLP REFLECTORS have this conversation. On there it's usually, "How do I get to Interstate 25?"... "How would I know? I'm driving on Interstate 5! You're asking on a system that's linked to a whole lot of other repeaters there, my friend!" (Heh heh.) There's also a lot of talk in past list discussions about how to get voted receiver systems to all sound the same. That's a challenge I haven't taken on yet, but hope to try someday. The concepts are similar, so it's a good thing to search the list archives and RB the website, for. So... there's some "stories from our system here" and some personal preferences. I just would find it VERY hard to install a different controller manufacturer's product after seeing some of the analysis and work that Virgil does/did on the S-Com boxes. His attention to detail on the audio chain is amazing... or they wouldn't sound as good as they do. The S-Com controllers have the audio headroom to handle any good (or BAD) sounding receiver audio I can throw at them, and reproduce it almost exactly out the other side. Yes, I'm an S-Com fan- boy. I've always admitted that. That's what I like in a controller... the audio headroom to push whatever I want through the controller and only be limited by the radios themselves. Then the debate about how it sounds on-air is a debate about how good a job I did on the receiver and the transmitter... the controller shouldn't "color" that analog audio signal I'm feeding it at all. It's a controller. I want it to control and ID, mainly... and I want it to do some other fancy things sometimes too (S-Com 7330!). If I wanted shaping, I would do something like you're doing, and use another box that shapes the audio. I want the controller to LEAVE THE AUDIO ALONE and pass it faithfully out the other side. There are some exeptions... like on the various 900 MHz repeaters that are using Motorola's HearClear technology... that seems to help the higher frequency stuff since it's so plagued by fluttering and noise due to the more line-of-sight nature of those bands. But for VHF/ UHF... I go for the "what comes in is what goes out" religion. -- Nate Duehr, WY0X [EMAIL PROTECTED]
