In video production, mixing sound involves combining audio from multiple sources and balancing them so they sound good to the audience. It also includes processing and routing audio, though that's a bit beyond the scope of this discussion.
Let's break down the differences between gain, trim and faders, terms that can be confusing for beginners in audio recording.
Gain and Trim: The First Step in Amplification
For all practical purposes, gain and trim do the same thing. Gain is the amplification that happens in a recorder's preamplifier. It takes a small microphone signal and makes it stronger, bringing it up to a level typically referred to as line level.
Most recorders have some form of gain or trim built-in to handle and record audio:
- Gain/Trim: Amplifies the initial microphone signal to a usable recording level.
- Fader: Used to adjust the volume of a specific channel within the overall mix.
- Mixing: Balancing multiple audio sources so they sound good together.
When setting up your audio, you adjust the gain before you start recording. The goal is to get each microphone channel to roughly the same level on the meters.
You do this by setting the fader to zero for all channels first, then adjusting the gain while people speak into their microphones. Aim for the meters to peak at a healthy level, well above the room's noise floor, but also leave some room for louder speech. This is called gain staging.
On quality recorders, aim for meters to top out around minus 18 dB, and no more than minus 12 dB. This extra space is called headroom.
It's important because if someone laughs loudly or shouts, the audio won't hit the maximum level (0 dB) and distort. Hitting 0 dB will cause distortion.
What Are Faders For?
The main purpose of faders is to create a mix. While gain gets the level to a healthy recording point, faders are used to blend sound from multiple microphones so they sound coherent.
The audience shouldn't have to constantly adjust their volume to hear different people. The sound should feel natural and balanced.
When actively mixing during recording, faders allow you to:
- Attenuate or reduce the level of microphone channels. You can pull down faders for louder talkers and push them up slightly for softer ones to balance everyone.
- Send the audio from a microphone channel to the mix at the level you've set with the fader.
It's also good practice to pull down the fader for anyone who isn't speaking for a while. This helps create a cleaner mix by reducing room noise and bleed from other microphones.
