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By far one of the least understood aspects of the Pro Tools Mixer is the Master Fader track. Many just assume it is a master volume control. And while it does affect the final level of a summing point or an output pair, understanding this track's function is critical in creating a mix that does not clip your converters. Well, at the same time uses as much of the system's output resolution as possible. So historically, if we think about a mixer and we think about the concept of headroom as it relates to summation across the mix bus, we can think about the summation of multiple electrical signals onto a single wire and if there is too much voltage running in that mix bus, it's going to start clipping or distorting.
Well, the way that analog consoles would clip or distort was actually kind of ear pleasing at some point. I mean obviously you could push them to the point of just destruction but there is a bit of gray area where you can kind of push it a bit hot and a lot of these consoles would sound even better than if you didn't push them. Well, in a DAW mixer, this couldn't be further from the truth. Because we are working in the digital realm, it either is or it isn't. So as to say that a signal is there or it's not. So once you exceed the mixer's clip point, it actually hard clips the audio, truncates the top of your waveform or the loudest part of waveform and creates digital distortion and this sounds really, really nasty unless that's exactly what you are going for.
So let me give you a little example. So if we think about individual tracks like small 24 bit buckets and these buckets combine into a larger 32 bucket, which is the mix bus. The Pro Tools LE mix bus is based on 32 bit floating point architecture and what that means is that even if we have really hot 24 bit signals, almost complete full buckets, as they add together, the entire signal will be able to fit into that 32 bit space.
No problem without clipping the mix bus. So you can add tons of hot tracks together and you are not going to clip the mix bus internally inside of Pro Tools. So this is all great until we have to go back out to our small bucket of a 24 bit converter. So the output out of Pro Tools is actually back in 24 bits again assuming we are running a 24 bit session. Now, what happens as we go from this 32 bits signal in the mix bus down to the output at 24 is truncation.
So if we have signal level that's too hot, right, we are going to be cutting off that level. And if it's too low, we are going to be cutting off the foot room of that mixer. Now, for lower level signals, it's not that much of a problem because generally these are below the converter's noise floor anyways. But for the hot signals, they get clipped and we get that nasty digital distortion right, that No Man's Land outside of where the converter can actually see, and so this is where Master Faders come in, in Pro Tools. So the Master Fader effectively lives between these two worlds of more headroom and less headroom between the 32 bit and the 24 bit world in this case.
So not only does it allow us to monitor the output of a signal as it exists in the mix bus and is summing across that mix bus, it also allows us to trim or select the output bits that we use at the truncation point. So effectively eliminating that clipped mix at the output. So another example would be think about a soccer field with a goal at the end. The ball can be kicked all over the field but at the end that goal is fixed in the middle and the ball has to exit the field through those two points of the goal.
Now imagine if you can move that goal up or down across the field to best capture the ball being kicked off the larger field. This is essentially what a Master Fader is doing for us. If a 24 bit output is our goal and our higher precision 32 mix buses is our field, the Master Fader allows us to adjust the output goal to best reflect our mix's signal level exiting the system, neither clipping nor too weak of a signal. So there are a lot of myths surrounding this. Many people think that you shouldn't use the Master Fader.
You should lower faders inside your mix. Most of these myths are completely inaccurate and you should definitely do your homework, but even if you don't understand this concept of a mix bus and higher precision and lower precision and bits and all that kind of stuff, it's not that complicated. All you really have to understand is that if you use a Master Fader in your mix like I have here, you want to make sure that that Master Fader is not clipping or it's not lighting the red at the top of your mix. So when you playback your mix let's say in the loudest section, you want to make sure it's not clipping the output.
And if it is, what you can go ahead and do is pull it down. So if I playback this mix -- (Music playing) [00:004:58.79] (Male singing: We hit the town...) Now if I push the Master Fader up to 12, we are going to hear tons of distortion. (Music playing) (Male singing: We hit the town...) You hear all that distortion on the symbols and the drums, and you can see that those lights are lighting up there.
So I want to pull this down until the output stops clipping. This is going to ensure that I'm not sending a clipped output to my 24 bit converter. Now, in this specific example, I have actually set the Master Fader to look at my Mix Bus rather than my main interface output and the reason I have done this is to be compatible with Pro Tools HD systems where Master Faders work a bit differently. It's beyond the scope of this course to get into the fine points of how the HD system works with Master Faders.
But there are some great articles that you can read on Digidesign's website. In fact if you are using an HD system, I highly recommend you go check out those articles. They are white papers in the Support section and they explain it in tons of detail. But as far as this session goes, what I'm doing is I'm looking at the summation point of the Mix Bus and so I'm using this Master Fader to ensure that any summation that's occurring over the Mix Bus is not clipping the outputs. I could create an additional Master Fader for my main outputs just to verify, just to make sure that I'm not clipping those converter outputs.
But the bottom line is you are using Master Faders to make sure that you are not sending a clipped signal to your output. Now, the other thing that we can do with Master Faders is we can use them to add session wide inserts, right. So they give us an insert point that affects all the tracks in the session or all the tracks being summed onto a specific bus. So in this case I'm using it to process the entire mix with a compressor, a stereo widener and a brickwall limiter. So I can sort of use my mastering style effects or mix bus style effects directly on the Master Fader.
Now, these inserts are post faders. So they actually take into account the level of your Master Fader as it goes from that higher bit world to the lower bit world. Now, this is important because if you drive this level into these plug-ins, it's actually going to affect the threshold of those plug-ins, especially if you are using any kind of limiting or dynamics plug-in. So you do want to make sure you understand that those are post fader inserts and how this level will definitely affect the signal going into any of these plug-ins.
So while they may seem difficult to wrap your head around at first, using the Master Faders effectively will allow you to create clean and unclipped mixes in the Pro Tools mixer and will serve as the final processing point for the mix bus and any mastering effects when finishing your mix. Again, if you are using Pro Tools HD or you do want more information on how the Master Fader works in a 48 bit mixing system like Pro Tools HD, I highly recommend you read those white papers on Digidesign's website because they can go a long way into making sure that the buses and the outputs of your mixes do not clip in Pro Tools.
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