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A Mastering Engineer’s View On A Quality Mix

A veteran mastering engineer outlines some of the most common problems he comes across when receiving mixes from clients...

By David S. Eley June 7, 2017

Image courtesy of Unsplash/Pixabay
This article is provided by The Audio Mastering Blueprint

Who is really responsible for a fantastic sounding master?

Mixing is justifiably a bigger subject than mastering and would easily fill a book or two by itself.

For that reason, rather than give a tutorial on mixing, I am simply going to outline some of the most common problems I have come across when receiving mixes from clients.

I won’t go into too much detail with things like, what frequencies to boost, or cut to improve the mix, or any other mixing tricks. I’m just going to try and get across an overall concept of why some mixes produce good masters and why others don’t. In doing so, I hope to shed a new light on this massive subject.

In a perfect world, all the problematic mixes I receive will go back to the mix engineer with a report on the issues I have found, followed by a remix, and then a great sounding master. The truth is, sometimes I have no choice but to make the best of a bad situation and master, to the best of my ability, a problematic mix. Having mastered many problematic mixes I am able to give some advice on why certain mixes don’t produce the best results, and why others do.

Mixing sounds together

There’s a fundamental rule when it comes to playing different sounds together at the same time. The lower down the spectrum the sounds lie, the more difficult they are to blend together.

I use a bass guitar playing two notes simultaneously as an example. If you play two different notes way down at the bottom of the bass guitar’s range then the two sounds will not sound clear, or very musical being played at the same time. Play the same two notes a few octaves up and all of a sudden it’s not so unpleasant to the ears hearing these two notes.

It’s unlikely in any song that the bass player will be playing more than one note at one time, but there are other factors that can cause there to be more than one thing fighting for space in the bottom end of the frequency spectrum.

Occasionally, I will receive a mix where the choice of kick drum is that of the tuned category. By that I mean, will have an obvious frequency or musical note contained within the kick’s sound. These are usually synthesized kicks or sampled (a natural sounding, and correctly recorded acoustic kick should not have any obvious tuned frequency or musical note).

When a mix contains a tuned kick, problems can occur as the note usually clashes with that of the bass-line. These conflicting frequencies at the very bottom end of the spectrum cause it to sound unclear and muddy. Tuned kicks have their place. In house styles of dance music, tuned kicks can sometimes be quite suitable so long as effort has been made to ensure the kick and bass-line work together.

Another rule is the more natural each sound is – as in how well recorded – the more easily they will mix. If when you record the sound of an acoustic guitar, the mic picks up some undesirable resonance of an untreated room causing certain frequencies to resonate, then this guitar may well be stubborn during the mixing stages.

When listening to a musical instrument in the real world, you would probably not notice room resonance unless you have a trained ear. To effectively record a musical instrument, you need to avoid placing the mic inside areas where the room is causing certain frequencies to jump out. Poor microphone placement will force the mixing process to be quite difficult.

A musical instrument itself may cause certain frequencies to jump out a little when the mic is placed close in to the body of the instrument. The resonating body of a musical instrument is how it produces sound in the first place, but there has to be some distance between a microphone and the instrument for it to sound correct. Only once the sound has travelled a certain distance away from the instrument will it form the natural sound of that particular instrument. Depending on what part of the instrument body you point the mic at, you will get a different sound. Some areas will be desirable helping you towards a nice mix, but some will not and will cause trouble.

A good mix starts here – microphone choice, microphone placement, suitable room, good musicians. If you get all this right then the mixing becomes much easier. You end up needing much less processing like EQ to persuade the mix to, well, mix.

When using the EQ technique described in my book, The Audio Mastering Blueprint (sweeping a boosted EQ across the spectrum), these undesirable resonant frequencies picked up by poor microphone technique are one of the things you are looking for. A very good mix will reveal little, or no unpleasant resonant frequencies when applying this technique – this is the best result you can hope for.


One major asset that all good mixes have in common is good separation. This is where all the many different things happening are clear and easy to pick out for the listener. So why do all the different sounds become so unclear and hard to pick out in the first place?

Resonance is one culprit. The resonating frequencies mask or blur other sounds occupying the same area in the spectrum. Also, when we hear sounds in the real world, the fact that they are all coming from different locations is one of the ways that the brain separates the sounds. When all the sounds are coming from a single set of speakers, some extra effort has to be made to allow the listener to separate all the different things going on.

This leads to an important point – depth. If effort has been made to give the mix depth then we are able to separate all the different sounds more easily. But before we get on to creating depth within a mix (not using Ultra Depth!), I’d first like to raise some awareness about the idea of separation and how it is so easily lost.

When two elements in the mix occupy very similar frequency ranges, it can become difficult for the listener to distinguish between the two. When a mix has many elements struggling to be defined, the mix may sound muddy, especially when it’s lower down in the spectrum. Throw in some unwanted resonance picked up during recording and the mix will become really rather stubborn.

Two sounds might occupy the same frequency range but have different textures, this would help them separate. Or, they might sit in different places in the stereo field which will help with separation too. Using the pan pot to separate sounds is good but you need to always ensure your mix sounds good in mono too, this is why EQ is an important tool for good separation.

Some advice I was once given was to start the mix in mono, get as good a mix as you can, then move to stereo.

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