Pro Tools Fundamentals - Master Faders

08-02-2014 09:00 AM

Talking about master faders can lead you into a discussion of some very technical stuff. I’m not going there in this article. While it’s really interesting, as long as you make sure you use master faders properly you don’t really need to know about dynamic range bottlenecks in TDM systems. Especially if you’ve only ever used Pro Tools 11.
The point of a master fader is to monitor headroom in your system. Headroom is something I feel strongly about. Considering how well current digital systems perform there is no excuse for clipping but every day I see people unintentionally ruin their audio by clipping it because they didn’t use a master fader.
It was perilously easy to unintentionally clip audio when using Pro Tools 10 and earlier, especially using TDM. TDM is a fixed-point system as opposed to the floating-point system used in Native systems. In Native versions of Pro Tools 10 and earlier things were more forgiving but since Pro Tools 11, Native and HDX systems are floating-point and with far greater bit depth than before throughout the application. This means that dynamic range is potentially almost unlimited but in spite of this monitoring headroom is just as important as it always was and the way to do this is using a master fader.
All Sessions Should Have A Master Fader

Although you might never touch it, your session should have a master fader - Why? The most important thing to realise about master faders is that the really important bit is the meter. That is why you are creating it in the first place, you might use the insert slots, you might use the fader but you will always use the meter and you need that meter!
Summing Points

Master Faders are created by the system at summing points in the mixer. Fundamentally the job of a mixer, whether hardware or software, is to combine (i.e. “mix”) signals together. A summing point is a place in the mixer’s signal path where this combining happens. If two signals are combined together there will be a new total value to represent the mixed signal - a voltage in an analogue mixer, a number in a digital system. This value will usually be greater than either of the incoming signals. So generally the more signals you combine, the greater the total output becomes.
As total summed output tends to increase the more tracks you combine, and also because many inexperienced mixers tend to turn up the quiet thing rather than turn down the loud thing when balancing tracks, it is not unusual to run out of headroom.
Example Session

In this example I have created a session with 10 mono audio tracks. I created a -20dB 1KHz sine wave on these tracks (select on the timeline and press option+ctrl+shift+3/alt+start+shift+3) and routed them all to a mono output. They will default to a stereo output but using option as “do to all” as per last week’s fundamentals article it is easy to change them to a mono output. In this case mono is simpler as it avoids considering a mixer’s panning law. I then created a mono master fader and assigned it to the same output as the audio tracks and then option clicked the mute button of one of the audio tracks to mute all.

If you build this session and un-mute one track you will see that the audio track’s meter and the master fader’s meter show the same value.

If you un-mute more and more audio tracks the master fader’s meter rises.

As you unmute the 10th track you will see all the headroom (the unused dynamic range) is all used up and the clip light will light. Now look at the rest of the meters. Nowhere else other than on the master fader was there any indication that clipping was occurring. That is why you need a master fader.
There are more things to say about master faders but the significance of the meter on the master fader is so important I thought it deserved an article all to itself. More thoughts on master faders to follow.