are involved on Radio Audio processing?
Must reed the following post.
cannot produce product they try fancy technical Equipment. Do you really think the
listener cares that you have OPTIMOD whatever? Of course, listeners will be turned off by
obvious Defects in audio such as earburn highs, distortion and other Artifacts. provide reasonably constant
levels, and peak limiting to keep the
For any station, a basic level of processing is necessary to
signal within FCC modulation limits. And on FM these days, since most everyone runs at
least the equivalent of a first or second generation Optimod, if you DIDN'T limit peaks
and control gain based on the the preemphasized signal, you would sound
loud that most every other station on the dial. Many broadcasters have this fundamental
belief that listeners will tune up and down the dial and listen to the loudest station
that they hear. I think this superstition
dates from the AM days of 50 or so years ago when receivers had much less AGC, and
signal strength really did make a big difference in how loud a station
would sound. loud the audio coming out of the
speaker will be, only how much noise is under it.
In any event, these broadcasters are still trying to get the last half db of
loudness into their signals, and I claim it doesn't make one iota of difference to their
Now, with FM, signal strength does NOT determine how
It remains true (fortunately) that radio programming is still an
art, not a
science, and so it's hard to say for sure what makes
the difference in growing or
shrinking the audience. However, the evidence
strongly points to program content as the primary factor and processing differences as
, how do you know what it's capable of? Just
because you've heard some stations that don't sound too good (and I admit there are some)
doesn't mean the Optimod is a fault. Firstly, it needs setting up correctly, it's not just
a case of plugging it in and running
If you've never played with an Optimod
away. It takes effort, over a period of time, as well
Secondly, the source material needs looking at. It's no good sticking mp3s through an
Optimod - that will sound awful. It's no good having your entire
music library on Minidisk
or PC. Voice processors on mic channels, overly
compressed promos, new Hyper-processed
& clipped CDís etc. are all good sources of distortion. The studio
engineer is unlikely to know what type of processor a particular radio station uses and
how it is set up for that station's preferred sound and
target radio type. The choice of
Optimod / IDT / Omnia or whatever and the settings applied varies a lot from station to
You will find multiband processors in recording studios because record producers like
their CDs to sound loud. Some studios engineers will apply multiband limiting (or worse,
clipping) to keep the producers happy even though this can destroy the waveform of the
music and, in particular, the peaks that Optimods love to get their teeth into.
The result of this double-processing is an unattractive distorted mush which is no louder
than pure audio would be straight into the Optimod.
Radio stations are also finding they have to increase the processing on their studio
voices to match the loudness of today's heavily compressed music. More distortion.
All of this comes to a head with digital radio where the coders need some light and shade
in the audio in order to know what to throw away.
A few independent record companies are starting to issue 'radio mixes' to major stations.
These are not clipped and sound far better on air, but it will take a major stand from the
radio industry to the big labels to end this horrible
practice. Optimod is a trade name
for a variety of signal processing widely used in broadcasting.
I have worked with Optimod-AM quite extensively and with products from competing
companies, and can state that properly set up, Optimod seems to do a decent job.
The Optimod system consists of basically three sections:
A wideband, gated AGC
A multi-band compressor.
Peak limiting and (in the
AM case) bandpass filtering; negative and positive peaks are adjustable separately for Optimod-AM.
The "gating" of the AGC amplifier prevents the AGC from going to maximum gain
during pauses in the program or otherwise quiet passages. The gating is adjustable to a
specific RMS level; with the gating off, it's a wideband compressor.
The multiband compressor is purported to have the time constants
and bandwidths required
for the most natural increase in loudness without audible effects. THe advantage of the multiband compressor is that,
judiciously used, it has the ability to equalise program material to
"uniform" sound. This isn't really a
bad idea when you own an AM radio station, and have less-than-ideal sources, from CD's all
the way down to your news reporter's cassette deck and Traffic Patrol.
Peak limiting is the time-honoured trick of increasing the RMS of the signal by,
deliberately clipping the peaks. The Optimod
does this reasonably tastefully, and allows you to adjust the clipping thresholdfrom -3 dB
to + 2 dB for negative peaks, and similarly for positive peaks. An elliptical output
filter allows this clipped audio to have reasonable overshoot characteristics when
it leaves the Optimod. The Optimod does have a phase scrambler (all pass filter) which
takes the assymetry out of normal speech and music programmes. This helps prevent certain types of transmitters
from grossly overmodulating during
"difficult" recordings. The phase scrambler might be in Optimod-FM as
Finally, there is parametric EQ after the wideband AGC, with both bandwidth, center, and
gain adjustable for bass and treble frequencies.
The Optimod-AM also has some adjustable single order filters for tilt and overshoot
compensation of older transmitters.
Orban do make other
products, such as Optimod-FM (the Optimod 8000 is mostly a stereo generator with
some compression, the 9000 being sort of the Optimod-AM with the stereo generator). When
Optimod-FM was introduced, it was the benchmark of stereo generators, and it is still damn
good. They also make a TV stereo sound system for BTSC.
Orban also manufactures a line of studio toys, such as parametric EQ, de-essers,
radio station has
pasted over the front panel so that it reads IM-AM (I guess
I personally like the Optimod AM, but the chief engineer at our Boston
Compression and EQ is a matter of taste and virtually
a black art. In the US, there is more anxiety over audio
processing and its
supposed relationship to cumulative audiences than probably any other
single thing in a major market station.
York David Anthony
WKTD Wilmington, NC