Gain Staging

A “gain stage” is any point in the signal path where gain is applied – where volume can be changed. Gain can be positive (makes the sound louder), negative (makes the sound quieter), or unity (doesn’t change the volume – but it’s still a gain stage!). “Gain staging” is the awareness that there are all these gain stages, and it’s important to carefully adjust each one so that each processing stage is operating optimally. This means balancing headroom and noise floor to keep the audio as clean as possible. 

The noise floor of an audio system is the level at which the background noise (hiss, etc) is. This is not the hiss in the recording, but the background noise inherent to the system itself. Generally, it’s best to stay as far away from the noise floor as practical. In analogue systems, the noise floor is hiss or hum caused by the electrical components. In digital systems, the noise floor is crunchy quantisation noise caused by a lack of digital resolution.  In modern digital systems, noise floor is not a big concern. Most professional analogue-to-digital converters (ADCs) have a noise floor below 100dBfs.

The headroom of an audio system is the amount of room (in decibels) between the ‘nominal’ level and the saturation level. The nominal level is level at which the audio spends most of its time. There is some flexibility in deciding what the nominal level should be. A low nominal level will give you lots of headroom, but a higher noise floor. A high nominal level will give you less headroom but a lower noise floor. The less headroom you have, the more saturation/clipping you’ll get, and the more compression and limiting you’ll need to keep the sound clean.

Noise floor is less of an issue in professional digital systems (especially all-software systems such as DAWs), but headroom is still critically important – even more so in today’s loudness war. If you don’t give yourself enough headroom early in the signal path, you’ll find yourself hampered by your need to reduce dynamics for technical reasons instead of focussing on sound.

-Kim.

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  1. July 27th, 2009
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