Mastering (sometimes called pre-mastering to differentiate it from glass mastering the stamper) is the act of making the final product sound nicer.  That does not sound like much, but the difference a decent mastering studio can make to a project is sometimes astounding.  There are also a huge number of bug-fixes that a mastering studio can do like reducing noise or taking out clicks and pops. Some mastering studios are hardware based using mixing desks and outboard and others just use computers and software.  Most seem to use a mixture of both, with many engineers preferring to get the basic sound right using hardware and then exporting the project to a computer for such tasks as de-noising and de-clicking.  The computer system of choice is often Sadie, though there are several PC and Apple based systems.

My first attempts at mastering were utter rubbish. Fortunately these were favours that I did for friends (who probably smiled politely and got them done properly elsewhere!) Then one day someone sent me a CD of classical music to be mastered and it sounded perfect. It was a string quartet and the sound was just exquisite. We agreed that if I did a good job, he would pay me, but if not, he will have to take it elsewhere and I go empty handed.

I was somewhat stumped as to what to do. It sounded great as it was. But I had to do something with it, so I put it into the workstation and brought the sound up on the desk. It still sounded lovely! If I did anything here, it could only be minute changes as the music was so perfectly balanced within the quartet.

But if anything was wrong with it, perhaps the mids were a little harsh, so I gently brought the mids down around 1kHz. And perhaps some of the highs were a little too sharp, so I put a de-esser on it; not much, but enough to soften the sound a little. And then the stereo image was a little flat, perhaps the result of close mic’ing. So I added just the smallest amount of M-S stereo enhancing, not too much, but enough that the stereo image reached the speakers. Then something told me to add a very small amount of a long, slow reverb. I tried the preset ‘Taj Mahal’ but kept it right to the back and only added it to the bass notes so that you could not really hear it, but you still had a feeling that you were listening to this lovely music in a nicer space.

I did an A/B comparison and I did not feel that I had changed much at all. It sounded softer and silkier, it sounded slightly more ‘professional’ but I did not feel that I had changed much. All the alterations I had made were so slight that the sound was more or less the same.

But the customer was thrilled and said that it was the best mastering job he had ever heard and was happy to pay me my full fee.

That is when I learnt that mastering is all about making slight changes, changes that make the music sound just ‘right’ but without changing the original feel of the mix.

I also learnt that it is much easier to master really good music.

There is a growing tendency for the large number of home studios to hand over projects unmixed or with a series of stem mixes (i.e. ready mixed stereo tracks of parts of the music such as rhythm guitars, drums, lead etc.) which have to be mixed together and then mastered.  Although many mastering studios would prefer to not to have to do both tasks, this is a welcome new source of revenue.

There are two models of charging for a mastering session. The traditional method was by the hour, but more and more studios are prepared to charge by the project. That means that the customer brings the project to the studio, who then quote him for a completed and finished project. Sometimes this also includes the cost of glass mastering and replication and even graphics for the CD cover. Again, all welcome new sources of revenue.

So let`s have a look at the tasks involved in a typical mastering session and what tools are used.

The first task is to listen to the music (switching between different sets of speakers) and think about what processes might be needed. The usual first step is to try a little e.q. If the studio is hardware based, a set of really good equalizers is vital. Very often, the music is improved by taking out a little of the mids. This has the effect of making the music softer (i.e. more `hi-fi`) so it is not always the right thing to do for hard rock.

Another tool often used at this stage is a de-esser, which is a fairly simple device for compressing high-pitched sounds so that they sound softer.. The raw mix often contains sharp sounds such as the esses and tees in vocals and often the cymbals are somewhat sharp and the application of a de-esser makes the sound soft and silky. There is a danger that even a moderate amount of de-essing can lead to a total absence of highs on some low quality systems such as car stereos, TV sets and radios. Another problem that can be solved by the de-esser is the harsh `digital` sound of poor quality AD converters. Some converters cause distortion at upper frequencies that sounds almost exactly like conventional essing, but is harder to get rid of. A de-esser can go a long way to soften these artifacts, but digital distortion is very hard to alleviate.

The next tool that is often reached for is surprisingly, reverb. This is usually in the form of a long and deep reverb that just adds a vague feeling of listening to the music in a nice space. Reverb can also be added to parts of the sound spectrum separately. The bass could get some added ambience to fill it out, or the highs could get a bright and lively sizzle added with the right reverb.

A stereo enhancer is a simple phase-shift device that has the effect of widening the stereo image. There is a certain amount of danger here as it will also make any reverb more noticeable and brings up the perceived level of background noise. A stereo enhancer can also cause instruments that were carefully panned slightly to the left or right, to be suddenly thrown all the way to one side. So anything that was not dead centre, could be hard left or hard right. But nearly all commercial rock and pop recordings use stereo enhancing as it makes the image wider than the spread of the speakers. The music sounds BIGGER.

A very common tool is the exciter which adds a certain amount of clarity to lead instruments and vocals when used sparingly. But here again, background noise and imaging can suffer when over used. It is often the case that the customer likes the effect of an exciter, but then the background noise level is increased with it and a single-ended noise reduction has to be used. This in turn can lead to drum hits having a `slappy` sound as the noise comes up on the snare hits and sometimes even with the click of the beater mic from the kick drum. An exciter also can show up little mistakes like clicks and pops that were never noticed when the original mix was made.  Exciters were more important in the age of tape, where multiple generations could lead to a muffled sound.

Without a doubt, the most dangerous tool in the mastering toolbox is the multiband compressor. As the name suggests, this divides the music up into different parts of the audio spectrum and compresses each individually. In the wrong hands (and sometimes even in the right hands) a multiband compressor can cause more damage to a recording than any other device or plugin. Even when used very sparingly, a multiband compressor can ruin a recording in such a way that nobody notices until it is too late, i.e. when the CD is pressed and in the shops and there is no going back! One of the problems is that radio stations (and pop/rock stations in particular) make heavy use of them, so even a mildly set multiband that has only been used to make the bass a little punchier can cause the whole song to `pump` in a very unpleasant way when played on the radio.

(For this reason, a so-called radio mix is usually the mix with a minimum of overall dynamic processing.)

But there are other problems that come with the multiband compressor. Studio monitors are usually high quality speakers that are more than capable of dealing with just about everything that you can throw at them. Even small, budget nearfields can cope with great disparities of signal, so too much bass in particular can be totally masked by the high quality of the speakers. The home hi-fi however, is often built of very cheap components and will rattle and `fart` on over-emphasised bass notes and often cheap tweeters will just not play those silky highs from the drums that you worked so hard to get right. These two mistakes can occur when a multiband is used to give the bass more punch and to soften the highs.

Two mottoes for all mastering tools must be:

1. Too little is infinitely better than too much.

2. When in doubt, leave it out!