cad@burdvax.UUCP (09/17/83)
Yes most stations use compression to avoid overmodulation. It is not required by the FCC. This is not really compression, rather peak limiting. Staions that use compression are trying to sound louder by increasing their average modulation. The problem in trying to "decode" the compression is that the amount of compression, and the attack and decay times will vary from station to station and from time to time as commercial stations strive to follow local trends and studies on listener fatigue.
wmartin@brl-tgr.ARPA (Will Martin ) (10/04/84)
As one who listens to FM both at home on a quality (my opinion :-) system, where I want wide dynamic range in the source material, and on a cheapy headphone radio, where I want consistently high-level audio to drown out the noise of the bus and the inane chattering and babbling of the other passengers who don't have the sense to keep quiet, I appreciate the dilemma of FM compression on classical stations. I would think the answer would lie in putting the compression in the RECEIVER, not in the transmitter. If car systems and headphone radios had built-in "automatic audio gain control" or suchlike circuitry, which would do to the received signal the same thing that the transmitter compressor/limiters do, would not that achieve the "best of both worlds" for both audiences? If such circuits were switchable by the user, you could enjoy full dynamic range in quiet environments, but compress the signal when it is necessary for it to override road noise or ambient sound levels. I thought most or all radios had some form of AGC in any case; maybe if it was slightly modified it could perform this function with little or no extra cost. Will Martin seismo!brl-bmd!wmartin or wmartin@almsa-1.ARPA
sjc@angband.UUCP (Steve Correll) (10/05/84)
> As one who listens to FM both at home on a quality (my opinion :-) system, > where I want wide dynamic range in the source material, and on a cheapy > headphone radio, where I want consistently high-level audio to drown out > the noise of the bus...I would think the answer would lie in putting the > compression in the RECEIVER, not in the transmitter. Unfortunately, when the compressor in the receiver boosts quiet passages, it will also boost noise and interference acquired during transmission. Instead, why not use a well-defined compression scheme at the transmitter? Then if you want wide dynamic range, you undo the compression at the receiver with complementary expansion; otherwise, you leave the signal compressed to drown out the noise in your listening environment. Stations which Dolby-encode their signal would produce roughly the desired effect, except that (a) Dolby compression is rather mild, and (b) Dolby compression is frequency-dependent, so therefore the stations mess around with the equalization in the transmitter. The unpopularity of the Dolby system among broadcasters suggests that they don't care much about our problems anyway. -- --Steve Correll sjc@s1-c.ARPA, ...!decvax!decwrl!mordor!sjc, or ...!ucbvax!dual!mordor!sjc
stern@inmet.UUCP (10/07/84)
#R:brl-tgr:-505400:inmet:2600107:000:1578
inmet!stern Oct 5 09:40:00 1984
Putting a compressor/limiter in your personal stereo unit is a good
idea, unfortunately, I don't think many FM radio stations -- especially
your HOT ROCKERS, are going to go along with it. Most radio stations
that turn their compressors up to the 75-80% marks do so because they
want to sound "loud". This helps when the station is on an adjacent
frequency to a competitive station: a top 40 station at 103.5 FM, and
an album station at 103.3 FM, for example. The top 40 station most likely
will crank up its compressor to make "dial-spinners" stop when they hear
the compressed Def Leppard screaming out at them. Classical music is
another story, as is jazz: A little compression is necessary to keep
the DJ voices from sounding like they are emanating from a tin can,
too much compression ruins the dynamics of the music.
I worked at my college radio station, WPRB-FM in Princeton, NJ, for
several years -- our format was classical in the early morning, jazz
until lunchtime, and progressive rock until the wee hours. For everyone's
benefit, we kept the compressor turned to 20% or so. The problem with
this is that we were adjacent to a *big* top 40 station, and when turning
the dial down through the 103's, you could skip right over us because the
top 40 station sounded so "loud."
This shouldn't be taken as a blast against top 40 stations -- some of them
are pretty good, and have a reasonablly clean sound. Some others sound
so much like AM radio that I have to laugh. Oh well.
--Hal Stern
Intermetrics, Inc. uucp: {esquire, harpo, ihnp4}!inmet!sternfigmo@tymix.UUCP (10/07/84)
Alas! FM stations wish they could do without compression, but there is no way many performances can be audible at their lowest and highest volumes, so some kind of medium has to be reached. THAT's why compression is used. If compression were not used, some parts of a performance would come out distorted, while others would simply not be audible. --Lynn
ron@brl-tgr.ARPA (Ron Natalie <ron>) (10/08/84)
The distortion you mention is a little ad-hoc compression by the tramsmitter. You can't let your FM signal deviate too much or you'll get into trouble with the feds. -Ron