Saturday, August 10, 2019

Radio Broadcast Audio Processing... Part One - The Studio Gear

For amateur radio, CB, pirate or even commercial broadcasting, your sound on the receiving end is very important. Why, you ask? I'll tell you!

Mainly, for all but high-kilowatt broadcasters, the listener is likely struggling to hear your station through interference from adjacent channels, lightning crashes, utes on channel, etc. It's kinda hard on the ears after a while. If your audio is distorted, clipping, raspy or noisy during pauses, it makes the listener fatigue even worse. And the sound your station presents to the speakers or headphones is affected in many ways between your source and the receiving end.

There has to be a balance, though. Yes, you want your audio to be loud and clear. But at the same time, you don't want it so squashed that it pulls up noise during pauses (WBCQ, anyone?) or has excessive midrange, presence, muddy sound or microphones buried under music. It's a LOT to comprehend. But it's easier than one might think.

First... your sources. This would be microphones, CD decks, PC audio, cell phone, tape decks, all that stuff. You really need a MIXER to control all of it smoothly. A mixer doesn't need to be really complicated. At home, I use an old radio console where I can switch each source between on the air, off and into a PC for recording or processing. My on-air is the PROGRAM buss, and the other is called AUDITION, which, ironically, is how I can rip a record into Adobe Audition.

You probably don't really need that much power in your mixer though. As long as you have the ability to listen to something in CUE or Pre-Fade Listen, say, to cue a turntable up, you really don't need mush more. The thing that will require that level of power is if you take phone calls live and want to send the caller mixer audio output without their own audio feeding back to them. In that case, you'd want a MIX-MINUS buss and probably a telephone hybrid, all beyond the scope of this tutorial.

Back to sources... Your MICROPHONE should be set up as the loudest thing on the board with the fader all the way up. it doesn't have to be pinned and clipping though. You just want to get it about 5dB above your other sources so it doesn't get "buried in the mix". So, set your input trims to where the mic is about 5dB hotter at full open fader than the rest of your sources. That will make sure your mic is heard clearly above the rest.

Many people install microphone processors between the mic and the mixer. It compresses, equalizes and limits the mic so it's level doesn't vary up and down as much as you talk. That is a  whole can of worms in itself... maybe in a later tutorial. Personally, I use an old 12 band rotary passive equalizer and a Urei 1176 limiter on my microphone, just to keep it consistent.

You need to now set the trim levels for all your inputs so they are not distorting or overdriving what gear is after the mixer when the various faders are all the way up.

The stage you just went through is called "setting the gain structure" of your audio chain. It *really* needs to be done first, or you will have much gnashing of teeth, newly-created cuss words and all of that! GO DO IT!

Now that your sources and mixer are properly set up, the real insanity begins... Processing your signal! This can range from relatively simple to "full-blown anxiety attack" as far as gear and setup is concerned. More gain structure setting, more fifty dollar terms you've probably never heard of, or probably wanted to know. It will require another part... I'll post that one in a bit. 





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