How to set gain levels
What is Gain?
Before we just crash on into it, what is Gain?
In the audio world and other areas involving electronics, gain is a measure of a circuit's ability to increase the power or amplitude of a signal. This is added from the input stage all the way to the output stage. Gain works by adding energy to the signal from a power supply. This is why if you keep adding gain, you keep adding noise that comes from adding extra energy/power.
Gain is needed because of the tiny voltage differences that are created from diaphragms of microphones. To be able to hear the reproduction of the microphone we need to add more energy to bring it into the threshold of hearing.
This will be determined shot by shot and scene by scene. There is no one size fits all for the right gain. What you should always be aiming for is, with the fader set to zero (fader pointing straight up) adjust the gain until the level of the people speaking is naturally hitting -18dB and is peaking no more than -12dB. This will be marked in different place for different meters, see which meter you are using.
Is there more than one stage of gain?
It is important to realise that radio microphones already have gain added to the signal to be transmitted across to the receiver. This means that you will be adding gain twice, so try to keep your radio microphone gain appropriate for the scene/shot by adjusting accordingly. This means you will be maximizing signal to noise ratio and have nice clean dialogue. I tend to have mine a little bit lower on the radio mics because my preamps in my 664 (Sound Devices) are cleaner than the radio mics internal one.
What is the difference to a fader then?
The fader is another gain stage but I will go into more detail in this article about faders.
How to set gain?
To sum up:
1 - place the boom or radio mic on the person and get them to talk in normal conversation.
2 - Make sure your fader is on ZERO (usually pointing straight up)
3 - If it is a radio mic, check you are not putting your gain too high on your mixer, if you are then adjust the radio mic to be louder. normal speech should be hitting around -20dB. Your boom microphones will always need more gain than your radios.
4 - once you are hitting the right levels use your faders to compensate in a scene.