Mixing : Volume controls part 1 - Faders

Volume faders control the volume of each sound in the mix, including effects.

David Gibson comes up with a very useful and detailed description about what all the studio equipment does and how does it affect our sounds in his book "The art of Mixing Second Edition"

Faders

Volume faders control the volume of each sound in the mix, including effects.

The level set for each sound is based on it's relationship to the rest of the tracks in the mix. When volume is mapped out as a function of front to back, you can place any sound or effect up front, in the background or anywhere in between by using the faders.

However, the level that you set a sound in the mix is not based solely on the Vader. If the level of the faders was the only thing that affected the volume of a sound in a mix, you could mix without even listening. You could simply look at where the faders are set on the console. There is more to it than that.

When you set volume relationships in a mix, you use apparent volumes to decide on the relative balance - not just the voltage of the signal going through the fader. The apparent volume of a sound in a mix is based on two main things, fader levels and waveform, and another minor one, the Fletcher / Munson Curve (See the "Fletcher/Munson Curve section below). First, the level of the fader does affect the volume of the sound. Change the level of the fader and the sound gets louder or softer.

Fader Level

When you raise a fader on a mixing board, you are raising the voltage of the signal being sent to the amp, which sends more power to the speakers, which increases the sound pressure level (SPL) in the air that your ears hear. Therefore, when you turn up a fader, of course the sound does get louder.

The decibel (dB) is used to measure the amplitude of the signal at each stage of this circuit. In fact, there are very specific relationships between voltage, wattage, and sound pressure level. Decibels are the main variables that affect the apparent volume of a sound. However, there is another important factor: The waveform of the sound.

Waveform (or Harmonic Structure)

The waveform, or harmonic structure, of a sound can make a big difference as to how loud we perceive a sound to be. For example a chainsaw will sound louder than a flute, even if they are exactly at the same level on the VU meters. This is because the chainsaw has harmonics in the sound that are irritating - or exciting, depending on your perspective. These odd harmonics are dissonant to our psyche, which makes them seem louder to us. Therefore, a sound, even if they are at the exact same volume in the mix. A minor factor contributing to the apparent volume of a sound is the Fletcher / Munson Curve.

The Fletcher / Munson Curve

The biggest problem with the human hearing process is that we don't hear all frequencies at the same volume - specially those at low volumes. (Fletcher and Munson did a study that shows just how screwed up our ears are.) This is why there are loudness buttons on stereos - to boost the lows and highs. You are supposed to turn them on while listening at low volumes. However, most people like extra lows and highs, so they leave the switch on all the time.  The main point here is that you should check your mixes at all volumes all of the time because you won't be hearing ass and tremble as much as you should. Also, whenever you do a fade at the end of a song, the bass and treble will drop out first. Technically, your ears give you the flattest frequency response at around 85 decibels.

Apparent volume is, therefore, a combination of decibel level, waveform, and the Fletcher / Munson Curve. But relax. Your brain has all it figured out. Most people has it all figured out. Most people have no trouble telling whether one sound is louder than another (although most of us need to learn to hear smaller and smaller decibel differences). Your brain quickly calculates all of the parameters and comes up with the apparent volume. All you have to do is listen to the overall apparent energy coming from each sound in the mix. It is apparent volume that you use to set volume relationships in the mix. You don't look at the faders; you listen for the relative volumes.

You can read more about the most important things you need to know about mixing, in Dave Gibson's book "The Art of Mixing 2nd Edition" A visual guide to recording engineer and production.