Dynamic Range in Radio, Audio and Life
What is It?
(THE BASICS)
A PRIMER FOR NON-TECHNICAL PEOPLE

PART 1
(First glance under development 8/17/07)

By Bob Burnham

Every so often I’ll dig out and share an article that has been in development but hasn’t been published officially anywhere yet.  This posting is the start of a very long piece.  I have spent a lifetime studying the work of those audio people smarter than me and listening to audio of all types.  This piece is my attempt to digest what I have grasped over the years and put it into an easier-to-digest form.

In this article, I have gone to some pains to make what could be to some a boring and deep topic at least a little more understandable and less boring to most people.

When to beginning broadcasters it SEEMS like we’re a little TOO nit-picky running good “levels” in the studio, this discussion will hopefully add some insight and some verification that there is actually some wisdom behind our pre-occupation.

At one time, not even a teenager yet, I wondered why songs coming out of a home stereo never sounded quite the same (or as “good”) as they sounded on the radio.  As I would soon discover, radio stations limit their dynamic range before feeding it into their transmitter.  It is done for several reasons which will be outlined momentarily, but for whatever reasons, it actually made the music SEEM to sound better.  The transients that might otherwise be distorted anyway, were squashed.  The bass that might otherwise interfere with clarity were controlled, the characteristics of the drum sounds and air talent voices were modified in such a way that made them seem more powerful. What was that mystique?  It was AUDIO compression and sometimes the audible side-effects which maybe we shouldn’t like, but we do.

As humans, we all prefer our day-to-day activities to proceed as smoothly as possible, with as little conflict or obstacles as possible.  When we travel, we prefer our flights leave as scheduled, our connecting flights synch up as scheduled and our hotel room to be ready when we arrive.  When we go to a restaurant, we don’t want to get into an accident on the way, for a table to be available when we arrive, our server to greet us and bring our food on a timely basis and for it to be of reasonable quality.  Hopefully they will accept our payment without incident that seems fair and reasonable for what was received.

We want our lives to progress in a constant flow with no rough edges, sort of like the waveform of a standard FM broadcast.  What happens within that restricted range of modulation that is within the realm of “acceptable.”?  (For the non-techies the waveform looks like a straight pipe with a bunch of “squiggies” inside). That’s probably what we would truly prefer, but it doesn’t always work that way.   

This is because life itself could probably be described as analog.  We’re not bits and bytes, and life may be more like the waveform of a standard AM broadcast.  We each live in our own little module of existence that constantly changes.  We interact, create more of us, or “things” or thoughts or modify the things around us. 

As analog creatures, we also create analog sounds, which for various reasons, we deem to be valuable enough to transport, modify, save or distribute.  The accurate transmission of those sounds so as to maximize the effectiveness of the listening experience is at the core of what this article is about.  It could also be why we can actually be emotionally affected by the way a radio station SOUNDS.  That is if that sound is close to or even resembles what our idea of great sound is.  Maybe the content is part of that reaction as well.    
In terms of sound, dynamic range is the difference between the softest sounds and the loudest sounds.

WHY AUDIO COMPRESSION IS A GOOD THING IN BROADCASTING
In broadcasting, it is necessary to limit the dynamic range to make it easier to listen to in a typical listening environment, to stay legal, have a “presence” on the dial and be competitive. If someone is punching across the dial and yours is significantly lower in volume than the competition, you will not be the station where they stop.  In a casual setting, this boils down to audio levels that are consistent.

You would think in a digital world, where dynamic range should be everything and classical and jazz music purists who don’t want the dramatic portions of their music damaged, a simple protective peak limiter should get the job done.  In reality, IT WOULD get the “job” done, but the station would NOT be competitive.

Back in the studio, someone who is just learning the fundamentals of broadcasting is told to make sure levels never exceed a certain point on the metering, but always averages ABOVE a certain level.  When the song ends, the voice should not “blast” the metering into “the red.”  This would be uncomfortable to listen to, aside from the fact it is considered “unprofessional.” Further, if the peaks go beyond the digital threshold, a truly harsh burst of distortion would be the result.

Historically, in the earliest days of broadcasting going back to the 1920s, there was actually an engineer who sat in master control at a radio station whose primarily job was to “ride gain” and make sure the transmitter was not over-modulated.  Using his best guess, his job was to ANTICIPATE what was coming next and be ready to compensate for that modulation peak that potentially, could actually damage the transmitter.


Various devices were developed in later decades that automatically took care of that and eliminated the job of just “riding gain” and can even “look ahead.” Such equipment will actually react much faster than a human.  Most of these devices, however, do work (and sound) much better if they are fed what’s known as a “good level.”  In a sense, digital processing is even more forgiving (as long as one doesn’t get to close to their absolute peak), but the garbage-in garbage-out mentality is still a good one:  If it sounds bad going in, it will sound equally bad coming out.  

In a practical Production environment, the “On-Air” grade of processing is not used nor is it even desired.  For that matter, your basic low cost wide-band processor is usually not use in a Production environment, either.

 In other words, one should get the basics down first.  Don’t rely on technology to fix carelessness or sloppy board work!

As already noted, in the Production studio, consistency of levels is, in fact, the key. In the music industry, not only consistency, but balance (both tonal and mixture of vocal and instruments) AND overall loudness (at the final mastering stage) becomes a factor.

Again, “limited” dynamic range boils down to the quietest sounds are made louder, and the loudest sounds are made quieter. You can’t understand audio compression without grasping this concept first. Also, don’t confuse DATA compression (such as what is used for mp3 music files) with AUDIO compression. 

There are various reasons as to why AUDIO compression could be called a good thing in certain applications.   Listening environment is a factor.  

When driving a car, natural road noise means when listening, you would have to crank up your radio during quiet passages. Except you may have noticed that you DON’T have to when listening to radio because radio stations limit their dynamic range – at least the popular music stations.  A classical, jazz or public radio station will probably be more conservative with their processing. With certain musical applications, limiting dynamic range is considered a very bad thing.  There can easily be too much of a so-called good thing.  Music loses its impact when over-processed.

HOW LIMITED DYNAMIC RANGE INCREASES STATION COVERAGE
On the plus side, in the analog world of AM broadcasting, a station will have greater effective coverage with a higher average modulation level.  This is because as the distance from the transmitter increases, so does the noise.  A station with higher (i.e. LOUDER) modulation will be more listenable at greater distances because the listener will not have to turn the volume up on their receiver as high as on a poorly modulated station.  When listening to a weaker AM station, when a listener has to turn the volume up, they also turn the volume up on BACKGROUND noise that is inherent to standard analog AM broadcasting.

The general public is not tolerant of a noisy, scratchy listening experience, and you won’t find many people listening to shortwave radio or distant AM stations these days.  But maintaining higher average modulation is still a consideration for lower power broadcasters operating on the AM band today.

COMING UP IN PART 2:
COMPACT DISC CHARACTERISTICS & “NORMALIZING”
© 2007 Robert R. Burnham

Bob Burnham is a broadcast engineer in the Detroit area.  He is rea
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