All broadcast transmission networks have at least a rudimentary degree of broadcast audio processing to reduce the dynamic range of program material. Now, “lower 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 fond of hi-fi and, furthermore, hardly any listen in hi-fi environments. Most will listen to it as they go about their daily life in the kitchen, in offices, in factories, driving the car, etc. These environments are “harsh” in terms of audio, so you need something to help your station eliminate background noise so it can be heard.
In its simplest form, an audio processor is just an audio limiter that keeps your transmissions legal by preventing them from being too loud (the technical term is “excessive deviation”). This is fine to keep it legal, but it doesn’t sound good when the limiter works. You could just set your audio levels low enough so that you never throttle, but then your transmissions 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 some added benefits too, however there can be difficulties too – streaming audio processors have many, many settings available, and when set incorrectly, they can make streams tiring to listen to, or just “awful”! That’s where the ‘black art’ comes in: when properly tuned streaming 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 smoothly increase the audio level. If things are getting a little noisy, lower it slowly. This feature alone alone is incredibly useful on 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. It splits the audio into multiple frequency bands (often 5 or more) so that the bass, midrange, and treble are processed separately. This avoids most / all the problems of the basic single-band limiters mentioned above. Each band is compressed in dynamic range, that is, the quiet bits are boosted and the noisy bits are lowered. This is similar to the AGC above, but is done 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 that you don’t drift too far. Non-streaming audio processors made by some of the cheaper brands don’t have this stage.
So that’s it in a nutshell. Broadcast audio processing is really important to your station. You can go for hardware streaming audio processing units like the Orban Optmod (in your dreams!), Omnia, or the more affordable DSPX, or there are various software solutions as well. On our website we have an audio demonstration of the impact of streaming audio processing. Check it out here: http://a-bc.co.uk/audio-processing/