A typical audio signal, whether it's one individual instrument or a multi-track mix, is usually made up of many quick transients whose amplitude values extend much further than the average level, or body, of the signal. These transients prevent us from raising the overall level of the signal too high. Because if we did, those transients would exceed zero DBFS, clipping our output converters and causing distortion. Now this presents a dilemma for our human hearing because our tuned average out-loudness over a longer period of time than a millisecond long transient hitting the top of our dynamic range.
So how do we get the average level of our mix up to a comparable level with the rest of the songs in our music collection? By clamping down on peak transients and raising up the average level of our mix using a brick wall limiter. Think of a mix going into a brick wall limiter like a spring being pushed into a concrete wall. Since the spring can never go further than the wall it is pushing against, the coils will simply move closer together, compressing the total length of that spring into a smaller space. Let's check out how a brick wall limiter works in a musical context.
Most brick wall limiters are easy to operate and have similar controls. I'm going to use the limiter built into my DAW for this example. But all of the major DAWs come with factory installed brick-wall limiters. In addition to dozens of third party limiter plug-ins you can purchase. Typically, how we use limiters to maximize the volume of a mix. Is by placing them as the last insert in the signal chain, usually on the master fader or output of the mixer. This allows the limiter to increase the average level while clamping down on the peaks internally before passing the final signal out to the D to A converter.
In this example, I have placed the limiter directly on the stereo example track, since I want to avoid limiting the guide dialog track you're listening to. I'll start by first lowering the output control to just under zero DBFS, say around 0.1 DBFS, so that the output from the limiter never exceed the converters maximum output. Now I can simply lower the threshold control which simultaneously increases into our 0.1 DBFS wall. Let's take a listen. We can see that it's working by looking at the game reduction meter.
Take a look at the wave form of the muted mix process track for a visual representation of what the limiter is doing. You don't want to push things too far, where you're literally flatten your mix and take all the life out of it. Potentially resulting in distortion. Take a listen to what happens if I pull the threshold down too far. Then I will slow down the release control, to help reduce distortion in the low frequencies. Sounds nasty huh. Even if I slow the release control, the distortion of a deep threshold is merely replaced with audible pumping as the limiter breath in and out.
Wheezing on the signal. Generally, I'm just going to go a few DB and check my work. Each track and limiter plug-in is unique and will be able to handle different amounts of limiting before breaking up. At this point, we don't want to add any plug-ins after the final brickwall limiter, as any additional level changes to our signal may clip the converters output. I like to evaluate what my brick wall limiter is doing by pulling down the output ceiling to the same level as the threshold, so I can really hear the limiting and not get fooled by the additional gain I've added.
One of the biggest mistakes novices make with these things, is they simply grab the threshold, pull down a whole bunch and say, awesome, it's so much louder. It must be better. But when we evaluate the processing without any net gain change to the signal, we can hear exactly what the limiter's taking away from our dynamics. Take a listen to as I reduce the output to the threshold value and switch the processing on and off. I will purposely use too much limiting so you can hear how the limiter is affecting the track when monitored without makeup gain.
Notice that if we go too far, we will lose all of the snap and bite out of our drums and percussion. One thing to note is that not all brick wall limiters are created equally. Some let you eke out a bit more average level without stealing your punch. While others start sounding pretty bad when you push them. Mixes with less brick wall limiting typically sound better when cranked up because the transients of the instruments are really allowed to work those speaker cones. Tracks destined for the club are big PA systems will do better with less brick wall limiting in greater peaked average ratio.
Tracks destined for further mastering, should almost always forgo the final stage of limiting, as this process can severely limit, no pun intended, what the mastering engineer is able to accomplish.
This course covers 26 techniques for improving your mixes with compressors, processors, EQ and filters, reverb, delay, and modulation. The first chapter covers compression and dynamics processing, including how to even out vocal performances and how to add punch to drum tracks. The second chapter goes into EQ and filtering techniques, such as creating complimentary EQ curves and EQ-ing FX returns. Next, the authors explore delay and modulation techniques, including using long delay on key lyrics and creating flanger and phaser effects. The last chapter explores reverb techniques including using gated reverb and supporting a track with regenerative reverb. .
Download the free exercise files and open them in Pro Tools to start training, or simply watch the videos here at lynda.com.
- Using compression to even out vocals and add punch to drums
- Maximizing mix loudness
- De-essing a vocal track
- Using EQ to fix problems and place elements
- Automating EQ
- Using long delay
- Creating slapback echo
- Creating a flange effect