Broadcast Audio Processing – the “Black-Art” of Broadcasting!

All broadcast transmission chains have at least a rudimentary degree of broadcast audio processing to reduce the dynamic range of the programme material. Now “reducing the dynamic range” might 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 buffs, and besides, hardly any are listening in hi-fi environments. Most will be listening to you as they get on with their daily lives in the kitchen, in offices, factories, driving in the car etc. These environments are “hostile” in audio terms, so you need something to help your station cut-through the background noise to make it listenable.

At its simplest an audio processor is just an audio limiter that keeps your transmissions legal by preventing them from being too loud (the technical term is “over-deviating”). This is OK to keep you legal, but does not sound nice when the limiter operates. You could just set your audio levels low enough so it never limits, but then your broadcasts would sound very quiet.

The answer is multi-band audio processing. Practically all BBC and commercial stations use this. The primary advantage is that it boosts the loudness of the broadcast, while preventing over-deviation. There are also some additional benefits, however there can be pitfalls too – Broadcast audio processors have many, many adjustments available, and when set-up incorrectly they can make broadcasts tiring to listen to, or just plain “horrible”! That’s where the “black-artistry” comes in – when correctly adjusted broadcast audio processors can make the whole station sound better and more professional – we are 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 programming (or guest) is a bit quiet, it slowly and gently boosts the audio level. If things are getting a bit loud it turns it down slowly. Just this function alone is incredibly useful in Community Radio where many presenters are inexperienced and have poor control of their audio levels
  • Multi-band compressor or limiter – this section is the clever bit. It splits the audio into several frequency bands (often 5 or more) so that bass sounds, mids and trebbles are processed separately. This prevents most/all of the problems of the basic single-band limiters mentioned above. Each band is compressed in dynamic range – ie: the quiet bits boosted and the loud bits reduced. This is similar to the AGC above, but done much more quickly. It is in this area where the “sound-signature” is created as it can drastically alter the tonal nature of the audio
  • Final limiter – this is a very fast-acting limiter that cuts any remaining signal peaks to ensure that your transmissions stay legal and you do not over-deviate. Non-broadcast audio processors made by some of the cheaper makes do not have this stage.

So that’s it in a nutshell. Broadcast audio processing is really important to your station. You can go for hardware broadcast audio processing units such as the Orban Optmod (in your dreams!), Omnia or the more affordable DSPX, or there are various software solutions as well. If you need some advice then we can help you – and remember our advice is independentGet in-touch

A demonstration of the impact of audio processing

Here is a demonstration of what broadcast audio processing can do. It uses the software broadcast audio processor called Stereo Tool, but it could equally use other software, or hardware units like the DSP-X or Optimod. No recommendation to to be implied by the video or those processor name-checks. Although the (peak) volume of the audio is not changed, you will hear a large step in the loudness of the audio when the processor is switched in and out. You will also notice a change in the overall “sound” of the music – generally sounding more “lively”.

The step in loudness created by the audio processing in this demo is no exaggeration. If you currently do not run audio processing, then you could get the same sort of increase in loudness and “density” to your programming. This louder (denser) sound will be easier to listen to in typical environments such as busy domestic settings, at work or in the car. It also, somewhat mysteriously it makes your station sound more professional, more like “real radio”! Don’t forget that as well as increased loudness, the audio processing will also mitigate for inexperienced presenters who run inconsistent levels in their programme. It is inconsistent levels that probably annoy listeners the most.

NB: apologies for the slightly distorted audio at the end of this clip – kind of undermines the point of it!  We’ll re-record it sometime.

As with all free information provided on this site, please use it at your own risk

Further Reading
Robert Orban: Transmission & Audio Processing
Introduction to Broadcast Audio Processing
Omnia – Audio Processing: A Retrospective


Associated Broadcast Consultants – Independent help and advice for Radio Broadcasters