4/05/09 This series of articles
re-published from www.radio-guide.com
issues of February to August of 2007 original on PDF format.
With this issue we start a new series of articles on audio processing.
While this article starts with a lot of History, the true focus of the series is the
current state of the art and where we are headed. Jim Somich takes us on
this guided tour.
Jim Somich’s career included positions as a major market Chief Engineer, Director of
for a group owner, and as the designer of a number of products, including the
FlexiMod FM Processor of his own MicroCon Radio System company.
(Radio-Guide February 2007)
Today, and Tomorrow by
author would like to thank Barry Mishkind, Bob Orban, Frank
Foti, and Corny Gould for their invaluable assistance in the
writing of this series.
Peaks to Power Audio
processing has its roots in the need to prevent over-modulation. In the 1950s, which some
consider to be the birth of modern day audio processing, it was also used to automatically
ride gain. But today’s broadcasters depend upon audio processors to do much more than
just ride gain. Is this good or bad for broadcasting?
PROLOGUE TO THE FUTURE Audio
processors are now almost completely controlled by one or more
wideband leveling to multi-channel, stereo-generating, look-ahead limiting and diversity
delay capable, in many ways, they are the heart of a modern broadcast station. The
importance of the arcane field of broadcast audio processing is evident by the extensive
work done in the field since the earliest days. From PROGARS through Uni-Levels and
Sta-Levels into the Audimax years, processing was evolving into an artform to be mastered
by a select adventuresome few. This is not merely an historical article, but to be
prepared for the acutely competitive future, we had better know a little about the past
and a lot about the present. This series will be a quick look at the past, a lingering
look at the present, and a glimpse into the future of broadcast audio processing, written
by someone who has “been there, done that.” The processing business will change
radically over the next few years and, in a decade, you will not even recognize it! I
think back to the 1980s and a young engineer I hired who had a certain gleam in his eye.
He did not have much experience but his enthusiasm was almost boundless. Little did I know
that he would go on to become a true rock star in the processing world. This article is
for you, Frank.
GOLDEN EARS One
thing is for sure: there will be new players on the scene along with many of today’s
superstars. I, for one, cannot wait to hear what they accomplish. While some
attempt to re-create the sound of the tube processors, the leading designers already are
looking ahead to new horizons of audio control. The names are legendary and few: Emil
Torick, Mike Dorrough, Bob Orban, Greg Ogonowski, Eric Small, Ron Jones, Steve Hnat, Donn
Werbach, Glen Clark, Jim Wood, and Frank Foti. Each had a vision of the way radio should
sound and made it happen. What a heritage: Audimaxes, DAPs, Optimods, Aphexes, and Omnias.
As processors became more sophisticated, creative engineers and programmers found ways to
use processing to develop a unique sound for their station. Some felt that a “wall of
sound” with virtually no dynamic range was the way to snag listeners. Others felt that
smashed audio only resulted in lower TSLs. The controversial world of modern audio
processing was born.
IMPROVE, OVERCOME Some
exceptional engineers, finding their hardware lacking, began to modify boxes to perform
tricks never anticipated by their developers. Another group went one step
designed their own custom processors from the ground up. In many cases, these custom boxes
became products literally built in garages and sold to the industry. Over the years,
successful audio processing has not been the province of large companies or groups of
engineers. In most cases, a single lone engineer with a vision struck out on his own to
capture his aural imagination in a “magic box.” But who will be the gurus of tomorrow?
And what will they have to work with? They are out there, working in the trenches. Guys
like Scott Incz, Corny Gould, and John Burnill have dreams that just might come true. It
is not as easy to hotrod a DSP processor the way one could change component values in an
Optimod or a DAP, but I know one thing for sure: there will be a new generation of
processing gurus and they will have new ideas. They will do things with their boxes that
we have not even dreamed of.
PROCESSING TIME MACHINE: YESTERDAY In
the beginning, there was no audio processing. AM radio stations kept the modulation levels low – perhaps 30% on average –
and used the technique of “manual gain riding” to avoid over-modulation. That meant a
live person sat with his
hand on the knob, trying to anticipate what was to come next. The
practice was reasonably successful, but hardly efficient. Failure to properly anticipate a
spike in audio level often resulted in the transmitter overloading and dropping off the
air – or worse. Even the behemoth WLW 500 kilowatt transmitter was operated in the
mid-1930s using only manual over-modulation control. The transmitter logs are replete with
descriptions of outages caused by modulation peaks. Most were brief, but some notes
indicated blown up capacitors, tube failures, and other problems that took longer to
MANUAL TO AUTOMATIC Gain
riding was an art, and practiced diligently by the studio engineers of the 1930s, 1940s,
and 1950s. When I started at WGAR, in 1959, almost all gain control still was
manually. By then there was a GE BA-5 peak limiter at the transmitter for over-modulation
protection, but one of the primary duties of a studio “engineer” was to ride the gain.
There was not a compressor in the entire studio plant. The chief had installed a chart
recorder in master control that made a permanent record of outgoing level to the
transmitter every minute of every day. Each morning, one of his stops was at the chart to
check up on the gain riding of the engineering staff during the past 24 hours. Each
engineer was held completely accountable for his shift. But, with the advent of
post-Television radio broadcasting with its combo operation, fast-paced shows, short
jingles and multiple elements, the need for an automatic form of gain riding became
PEAK LIMITERS FOR AM The
first peak limiters came to market in the mid-late 1930’s. RCA introduced the 96A in
1936 and this may be the very first commercial peak limiter to hit the market. Western
Electric introduced the 1126A in 1939. But you could hardly call these boat anchors audio
processors. They were basically mundane tools to eliminate over-modulation, pure and
simple. The PROGAR (PROgram GuARdian), developed by Al
Towne at KSFO,
in 1935 really was the first known audio processor: a combined intelligent compressor
(automatic gain control - AGC) and peak limiter. But it took more than ten years for Towne
to patent it, sell it to Langevin and bring it to market. Then something exciting
happened. Peak limiting became much more sophisticated. Even today we would have to agree,
it was ahead of its time.
Early peak limiting kept the transmitter on
The PROGAR brought automatic gain
control and peaking limiting together
THE PEAKS In
1947, General Electric introduced the BA-5 delayline peak limiter and it took the
broadcast industry by storm. It was cleaner than anything that came before because it used
a feed-forward limiting scheme and a delay line to “give the audio a change to catch up
to the bias generator.” How clean was it? Back in those days, NBC had an iron-clad rule
that they would only use RCA equipment. Yet, they bought BA-5s and removed any evidence of
GE manufacture. They repainted them RCA umber gray and added the RCA meatball. Magically,
the new “RCA” peak limiter was born! Every NBC O&O began sounding much better
thanks to some “
engineering.” GE did not rest on their laurels either. They continued their dominance of
the peak limiter market by introducing the BA-6 in the early 1950s and the BA-7 in 1957.
These boxes were really unique. To make a long story short, the input audio modulated an
RF carrier and all peak limiting was applied to this carrier. After demodulation, the
audio was fed to the transmitter. Many processing artifacts were eliminated by this
scheme, but it was an absolute bear to keep in alignment and it took two engineers or one
bodybuilder to wrestle one into a rack!
TO PROCESSING Throughout
the 1950s, many FM stations eschewed audio processing entirely. I remember one old-timer
studio operator telling me that “you really couldn’t overmodulate the FM.” Later,
some FM stations installed a Fairchild Conax preemphasized clipper to tame the
pre-emphasis, but that was all. In fact, it was not at all unusual in those days to watch
the modulation monitor “pin” on muted trumpets even when using a (conventional) peak
limiter. There was quite a way
yet to go in developing effective FM processors.
most important part of a compressor or peak limiter is the gain control element. During
the early years, this was usually a tube. The PROGAR used a 6L7 heptode tube. The 6L7 was
designed as a variable mu (amplification) tube – that was the purpose of the extra grid.
All tube compressors and limiters functioned by mixing
a DC control voltage with the audio
at the grid of a variable mu tube. These amplifiers
used push-pull operation so the control voltage could be effectively canceled at the
output. This reduced the “thumps” that were common when these boxes got out of balance
due to tube aging.
were a few remote cutoff tubes designed before the GE-6386, but this tube became the rock
star of the 50s in audio processing. It was the basis of the GE Uni-Level, Gates Sta-Level
and Level-Devil, and the CBS Audimax. The 6386 was a remote cutoff dual-triode, which made
it ideally suited to push-pull gain control operation. A remote-cutoff tube has a grid
that is wound in a nonlinear fashion and this gives the tube the unique characteristic of
reducing its mu with increased signal levels. This was a valuable characteristic in a
compressor or limiter. Conventional sharp-cutoff tubes tended to operate with
substantially more distortion and artifacts. The Gates Sta-Level was a straightforward
the 6386 as a gain control element. A 6AL5 dualdiode was used to rectify a sample of the
output from a pair of 6V6 tubes operating push-pull. This DC control voltage was fed, via
an R/C time constant network to the grids of the 6386 tube. The circuitry was very similar
to the GE Uni-Level, which preceded the Sta-Level by a year or two. The Gates Level Devil
added a level dependent expansion gate that released about 10 dB of expansion when the
input level was above “noise level.” This gate did not work
well and resulted in a lot of “sucking and wheezing.” However, those were the humble
roots of intelligent audio processing.
The Gates Sta-Level, a solid performer used
well into the 1970s
The Volumax 400. Together the Audimax and
were known affectionately as “The Maxx Brothers.”
CLEVER MARKETING SCHEME The
year was 1959 when CBS Laboratories introduced the Audimax I. Designed by Emil Torick and
marketed specifically as a “gain rider,” the Audimax I made no pretense to being an “audio processor.” Yet, the
unique design of the Audimax ushered in the era of audio processing. The Audimax I was
also the first broadcast
audio processor to be sold on a 30-day trial basis. A broadcaster
could submit a purchase order for a unit and put it on the air for a month. If they were
not happy with the sound they could return it at the end of the trial period with no
questions asked. I am sure they got a few back, but the vast majority of users were quite
satisfied with this box. I believe the original price was around a kilobuck (in 1959
dollars) and most of those who gave it a try became true believers in the Audimax concept.
The Audimax I
MAXX BROTHERS Just
like in the Uni-Level and Sta-Level, the 6386 dual-triode was used as the gain
element, but with enhancements. A “platform mode” of control kept the Audimax gain
constant over a 6 dB gain platform. This resulted in a lot less “busy-ness” in the
sound. Should the input audio move outside the platform range, gain was quickly readjusted
to define a new platform. The Audimax II quickly followed, which added an adjustable noise
gate that froze the gain when input level fell below a user adjusted threshold. The
Audimax II-RZ added a “return to zero” function which did just what you might think.
It slowly returned gain to the zero gain point during periods when the input audio was
below the threshold of the gate.
Audimax really started something and it transitioned into solid state versions and later
added a biaseddiode peak limiter called the Volumax. The development of the Audimax was
indeed a megaevent in the history of audio processing for broadcast. The “Maxx
Brothers,” Audimax and Volumax, ruled for a decade and continued to be in demand for
another ten years after that! Truly a remarkable record. In its later years, Thompsen
acquired the Audimax line and produced a thin, one rack-unit version of the Audimax and
OF MODERN DAY AUDIO PROCESSING There
were several modifications applied by engineers who just could not accept the parameters
that were fixed in the units. Most of these were attempts to speed up the release action,
but there were many others. It seemed like every creative engineer had his own set of
Audimax and Volumax tweaks. Basically, General Electric and CBS Laboratories ruled the
roost when it came to state-of-the-art audio processing in
the 1950s and 1960s. But
nothing stays the same – and things were about to change big-time in the 1970s.