Audio Levels

Having a good understanding of the importance of audio levels is often overlooked.

Broadcasters on Television and Radio have to take great care to ensure levels do not clip (i.e. become higher than the platform can handle) as this can cause distortion resulting in viewers/listeners switching off.

At acquisition is is important that sound engineers set the equipment up appropriately to ensure thay can capture eveything they need to.

Most domestic equipment uses Automatic Gain Control (AGC), this does have a place in broadcast but most audio engineers choose to have more manual control over the gain applied to the signals captured by microphones.

DeciBels (dB) are very poorly understood despite being the main way we measure audio levels.

The important takeaway from the first video is that dB’s express a ratio and on their own a ‘dB’ value doesn’t tell you anything. For it to be useful it must state its reference, which is normally done via a postfix (e.g. dBA) or absolute value in brackets (e.g. dB(1V)).

In Digital audio we typically use dBFS (i.e. relative to Full Scale – essentialy the maximum amplitude capable for a sine wave without clipping). Because the reference level is the maximum possible, all digital audio levels have negative values with the lowest possible value (i,.e. mute) being around -96dB.

When it comes to visualising audio levels there are a wide range of audio meters. The most common is the VU meter which is cheap and easy. it is an analogue scale where 0VU relates to a particular analogue peak-peak voltage on a wire. Broadcasters typically favour the PPM (Peak Programme Meter) which is a more complex meter with fast rise time and slower fall time making them easier to read and show more realistic peak values. PPMs are common across Europe but there are many different scales/numbers applied to them. One of the videos below discusses their use in BBC Radio in the UK, it also highlights the audio compression used on Radio 1.