rjr@mgweed.UUCP (01/17/84)
I agree with Dave Sewhuk's comments on FM stations. As far as I know, peak limiters are still required in all radio stations, AM or FM (and TV audio too). Theses devices prevent audio peaks from exceeding the 100% level (in FM this equates to 75kHz deviation). The peak limiter is an AGC amplifier with fast attack and release times as opposed to compression amps that have a slow decay time (1 second or so). It's been a while since I worked in broadcast but it seems to me there was a requirement (at least for AM stations) that the average percentage of modulation had to be above 75 or 80 percent. That is impossible to do without some kind of processing. I don't know what WFMT in Chicago does except perhaps to keep their level down low enough so the peaks seldom reach the limiting point. At times their level is awfully low, but they certainly have dynamic range. Someone on the net said the received quality would depend how far one was from a station. Distance makes no difference if the signal is full quieting and there is minimal multipath. I am 40 miles from the Chicago stations and I use a 12 element yagi with foam coax to my tuner to get the best signal strength. Dave, I think FM stations can change over from the standard 75us pre- emphasis when sending Dolby type source audio. The pre-emphasis at the transmitter "gooses up" the highs. The receiver has the opposite curve (75us de-emphasis) so the overall response is flat. This improves the signal to noise ratio. The same type of thing is even done with FM 2-way radios (20db from 300 to 3000 Hz). Tapes and discs use different types of equalizations (NAB and RIAA to mention a couple). I don't consider these "treatments" of the response curves as being "processing" as such. They are used to correct an undesirable condition that would cause overload in the bass region that would occur if the recording were flat. Bob Roehrig
frenchie@ihu1e.UUCP (01/18/84)
As a remote engineer for WFMT, I can honestly say that they usually broadcast my recordings of live events rather faithfully. However, their general manager is of the belief that WFMT should sound as loud as the rockers on either side fo them. So recently, they have increased their levels into their limiter (YES!! They do use a limiter!!) and I can audibly hear them banging it pretty hard lately. DISGUSTING!!! Jerry LeCompte AT&T Bell Labs - Naperville,Il.
crandell@ut-sally.UUCP (Jim Crandell) (01/18/84)
I wouldn't launch into WFMT too hard for using a limiter; as I
recall, the FCC doesn't give them too much of a choice. As for
running into the limit, well, that topic's been spoken to.
WRR in Dallas (101.1) has a very similar problem with a pair of
high-level carriers (one rock and one miscellaneous plplplpl)
at 100.3 and 102.1, if memory serves. WRR, however does not make
a habit of ramming the modex limit, and I find that when I reach
DeSoto on the Interstate -- at which point I should be in range --
I can never find WRR, unless something loud is going on at the
moment. Blame it on the neighborhood.
--
Jim ({ihnp4,kpno,ut-ngp}!ut-sally!crandell or crandell@ut-sally.UUCP)