Pro Tools Fundamentals - Master Faders Part 2

08-09-2014 10:00 AM

In last week’s fundamentals article I looked at the importance of master faders in monitoring headroom. Having looked at the potential problem of running out of headroom the next thing to consider is what to do about it?
Shoud I Turn Down Tracks Or Master Fader?

There are two obvious solutions, either turn the master fader down or turn down the tracks feeding the master fader. Anyone who has spent a lot of time using analogue mixers will probably intuitively think that turning down the master fader won’t fix the problem. In an analogue mixer the master fader is an attenuator which can reduce the level of a signal so it won’t clip the next stage of the signal chain, but if the audio has already overloaded the buss then it won’t help with that. The only way to free up headroom is to turn down the channels feeding that buss. However the mixer in Pro Tools is not an analogue mixer and floating point mixers are often counter intuitive to people who are used to analogue gear.
In a simple session there is no reason not to deal with the problem at source and turn down all the faders feeding the output. This would be laborious if not for the “All” group which is automatically created in all Pro Tools sessions. Simply enable the all group, turn down your faders until headroom is restored and option-click the master fader to return it to zero. This is my preferred method when introducing this issue to new users. I recommend they try this method first as it helps illustrate what the problem is and how to fix it in easily comprehensible terms.

This method of turning down the source tracks is useful from an educational point of view but it is largely historic nowadays as in Pro Tools 11 turning down the master fader will fix the headroom problem and it won’t interfere with anything else in your session. There are lots of occasions when turning down source tracks can have unwanted consequences. Post fade sends will be affected as will dynamics processing on sub mixes, there are many other examples but the main point is that adjusting a master fader affects the available headroom and nothing else.
There is an excellent explanation of some of the points brought up by this in the disqus comments from last week’s post which I thoroughly recommend. Many thanks to those who commented.
How Many Master Faders Should I Use?

So If master faders are so important, should I display them on every output? Every buss? Well while it is perfectly justifiable, it might end up being counter productive. In practice some things are more likely to clip than others. For example in my experience its fairly common for cue mixes to clip but I’ve never run out of headroom on an effects send. Its a matter of opinion but what I tend to do in a typical music session is have a master fader on the stereo output and a master fader for each of the cue mixes.
Converters Have Less Headroom

There is an important distinction to be made here between summing points feeding outputs and summing points feeding busses. I don’t think its necessary to get into a technical discussion about how dynamic range works in a floating point environment but while Pro Tools has an enormous internal dynamic range, DA converters have a fixed dynamic range of 144dB at 24 bit. Although you might be working with 1000dB dynamic range within your system you are still limited to a theoretical maximum of 144dB in and out of your system. In Pro Tools 11 you may have noticed that some clip lights which previously were red (like a clip light should be) are now amber. These amber clip lights replace the traditional red lights on master faders for busses. They are a warning that although, because of the floating point mixer, clipping hasn’t occurred. If the (floating point) buss were changed for a (fixed point) output, clipping would occur.

Inserts On Master Faders Are Post Fader

The last important difference between master faders and other tracks in Pro Tools is that the insert slots are post fader. This used to be particularly important in Pro Tools 10 and earlier because of the dynamic range available to TDM plugins. An excellent example of the difference this makes is the effect it has on limiters and compressors on the master if you attempt a fade out using the master fader. With a limiter on a master fader, as the fader level is dropped, the signal feeding the (post fader) limiter is reduced, resulting in less and less limiting during the fade. If the insert slots were pre fader, as they are on other tracks, the amount of limiting would stay consistent during the fade. This has led to the common practice of feeding a mix buss via an auxiliary input and processing from there.