Broadcast Audio Processing – The “Black Art” of Broadcasting!

All broadcast transmission networks have at least a rudimentary degree of broadcast audio processing to reduce the dynamic range of program material. Now “reducing dynamic range” may sound bad in a hi-fi sense, but don’t let that put you off. In the real world, most of your listeners are not hi-fi enthusiasts, and furthermore, almost none listen in hi-fi environments. Most will listen to it as they go about their daily lives in the kitchen, in the office, in the factory, driving the car, etc. These environments are “hostile” in terms of audio, so you need something that helps your station eliminate background noise so you can be heard.

In its simplest form, an audio processor is just an audio limiter that keeps your streams legal by preventing them from being too loud (the technical term is “excessive deviation”). This is fine for legality, but doesn’t sound good when the limiter is working. You could just set your audio levels low enough that it never caps, but then your streams would sound very quiet.

The answer is multiband audio processing. Virtually all commercial and public service stations use it. The main advantage is that it increases the volume of the transmission, while avoiding excessive deviation. There are also some added benefits, however, there can also be pitfalls: Streaming audio processors have many, many settings available, and when set incorrectly, they can make streams exhausting to listen to, or just plain “horrible”! That’s where the “black art” comes in: when properly tuned broadcast audio processors can make the entire station sound better and more professional, we’re not exaggerating!

Broadcast audio processors typically have three main stages:

• AGC – Automatic Gain Control – this section acts a bit like a technical operator sitting in the studio. If the schedule (or the guest) is a bit quiet, slowly and gently increase the audio level. If things are getting a little noisy, turn it down slowly. Just this feature alone is incredibly useful in Community Radio, where many presenters are inexperienced and have poor control of their audio levels.
• Multiband Compressor or Limiter – this section is the smart part. Splits audio into multiple frequency bands (often 5 or more) so that bass, midrange, and treble sounds are processed separately. This avoids most/all of the problems of the basic single band limiters mentioned above. Each band is dynamic range compressed, ie quiet bits are boosted and noisy bits are reduced. This is similar to the AGC above, but does it much faster. It is in this area that the “sound signature” is created, as it can drastically alter the tonal nature of the audio.
• final limit – this is a very fast acting limiter that cuts off any remaining signal peaks to ensure your transmissions remain legal and you don’t drift too far. Non-broadcast audio processors made by some of the cheaper brands do not have this stage.

So that’s all in a nutshell. Broadcast audio processing is really important for your station. You can go for hardware streaming audio processing units like Orban Optmod (in your dreams!), Omnia or the more affordable DSPX, or there are various software solutions too. We have an audio demonstration of the impact of streaming audio processing on our website. Check it out here: http://a-bc.co.uk/audio-processing/