There are some approaches and concepts in mixing which are essential to what we do. Here are three things which really make a difference..

Mid Side

Mid-Side is one of those things which when first encountered can seem like magic. It is of course nothing of the sort but it is very clever and very cool.

If you’re hazy on the details, M/S is an alternative way of capturing, processing and presenting plain old stereo. In a stereo signal there are some things which happen on both channels and other things which do not. The stereo cues which our brains interpret to create a convincing stereo image rely on audio which is largely common to both sides with some differences between the channels to create a phantom centre with a stereo panorama stretching between the speakers. If the two sides of a stereo recording had no common information between them you don’t have stereo, you have two speakers playing different things - dual mono.

The processing required to isolate these two elements, the ‘mid’ and the ‘sides’, just requires the left and right signal to be added together to create the sum channel, or to be subtracted from each other to create the difference between the signals. Sum and Difference or Mid and Sides. Same thing.

How Vinyl Works Helps Visualise M/S

An excellent example which can help people visualise the relationship between LR stereo and MS stereo is to consider how vinyl records work. Specifically, how can a single groove and a single stylus reproduce stereo? Shouldn’t there be two grooves?

The answer lies in the fact that while there is only one groove, there are two sides to that groove and if one side changes while the other does not, then the stylus will move diagonally. Using compass points as a reference either in a NW-SE or a NE-SW direction. So if amplitude changes in either stereo channel are represented diagonally, what happens NS or EW? If both channels move in the same direction at the same time (i.e. are the same as each other) the needle will move up and down and if they change in opposite directions (i.e. are different from each other) it will move side to side. Sum and Difference AKA Middle and Sides.

So there are two ways of presenting stereo, so what? Well actually quite a bit. While it’s not difficult to set up the required processing to convert LR stereo into MS stereo, or vice versa using just a mixer, it’s even easier to use a plugin and many free tools provide MS matrixing as a feature. if you listen to just the Mid channel you are hearing the information which is the same on both channels. If you play exactly the same audio out of both speakers you have a mono mix. So the Mid channel is the mono component of a stereo mix - instant mono check.

The sides, or difference channel is more interesting. The difference between the two channels of a stereo signal, when replayed typically contains lots of reverb, elements or instruments which are hard-panned and very little of the central elements of a stereo mix. It can be a revealing insight into favourite music to audition just the sides and check out the vocal reverb on its own, or hard panned backing vocals without the lead. Try it.

Ways You Can Use Mid Side

But further than the novelty factor, Mid side can be incredibly useful. Firstly as a method of capturing stereo recordings. The Mid and Side elements of a stereo recording can be captured directly by using the correct polar patterns. To record only the information happening directly in front of the mic array a forward facing cardioid mic is a good choice, and to record everything happening to the sides a fig 8 mic placed at 90 degrees will hear the sides but will be deaf to the front. Combining these two mics with an appropriate polarity inversion results in conventional stereo but with two advantages.

The first advantage is that if you mute the Fig 8 mic you have a mono recording. Cardioid mics sound best from directly in front. A technique like XY would combine the sound of two cardioid mics if used to create a mono version, two capsules, at slightly different points in space and both off-axis. Not ideal, whereas MS mic arrays are inherently mono compatible.

The second advantage is that the width of an MS array can be varied by changing the level of the sides channel. Turn it down it gets narrower, turn it up it gets super-wide, though be careful with this!

A third advantage is that MS arrays are inherently symmetrical. With other stereo techniques well matched mics are important as differences in level and frequency response will skew the signal. No such problem with MS and while well matched mics are still advisable, any difference between the cardioid and fig 8 mics will be the same on both channels so while it might be coloured, it will be coloured the same on both sides.

M/S Processing

A second way you can use Mid Side is for processing. With the Mid and Sides components seperated out from each other, different processing can be applied to each. For example, as bass and midrange heavy elements frequently occupy the centre of the mix, EQ adjustments can be made there without affecting the sides, or compression can be applied selectively to the middle and sides. The possibilities are endless. Many plugins have MS features built in but MS encode and decode plugins can be applied, with conventional stereo-only plugins in between these working on the MS signals.

Mid side is especially useful on complex signals where it can be used to selectively target elements within a stereo signal. For this reason its popular in mastering and if, for example, you want to brighten the cymbals without affecting the vocal but don’t have access to the multitrack, MS processing can be a solution.

Delta Solo

Delta in this context refers to what is left when you subtract the original audio from a signal which has been treated in some way. The result is the difference between the two - that word ‘difference’ again. The way you do this is to sum a polarity inverted version of the original audio with the processed output. If the two are identical (because no change was made) the result will be silence - perfect nulling. If a process is applied to the audio it will introduce a difference and the dry and wet versions will no longer null, leaving only the difference audible.

It’s easy to set this up yourself in you DAW using duplicate tracks with switched polarity on one copy only. If you’ve never tried it experiment with an EQ and you’ll quickly get the idea. A place you’ll find ready made delta buttons is on dynamic processors where they can be invaluable for fine-tuning attack and release settings and on de-essers where they can help you target the audio you’re trying to control. There is also the related Band Solo feature found in EQ plugins which helps you find offending frequencies efficiently.

To see Delta Solo in action check out the video below in which Luke demonstrates how to use it in any DAW and with any plugin.

Loudness

Loudness workflows used to only be of concern to people working in post production but what was initially used as a way to address inconsistencies in broadcast has ultimately provided the solution to the Loudness Wars which plagued music production for so long. If you don’t yet have a handle on LUFS and you’re uploading music to streaming platforms someone else is doing it for you, and with less care than you would do it yourself!

‘Loudness’ is the perceived strength of a piece of audio, how loud we perceive it to be and this can be affected by level, frequency, content and duration. It’s not only about level. Level is an electrical measurement, of the audio signal, whether it’s analogue or digital. Loudness is related to level but isn’t quite the same thing. For years there was no reliable way to measure loudness. The earliest way we measured loudness was to measure the RMS value of an audio signal mainly using an analogue VU meter. The dynamics of the VU (Volume Unit) meter proved to be a remarkably close approximation to the perceived loudness of the audio being measured, but in recent years the Loudness Unit (LU) was developed which is a more reliable measure of perceived loudness. With the means to measure it properly in place the industry has made huge progress, first in broadcast and post production, and with the rise of music streaming platforms, into music production. If you work in audio in 2023 you need to understand Loudness workflows and delivery specs. We have comprehensive Loudness resources available here on Production Expert so if you need additional information check out the resources below.