Channel & Bus Compression
Some problems I come across when mastering are not always to do with muddiness or tone, sometimes it’s down to compression. Let’s start with the drums.
Compression can really change the tone or feel of the sound you are compressing and this happens mostly to percussive sounds down to their sharp attacks. Because a percussive sound happens so quickly, with quite a large amount of changing tonal information hitting you in such a small amount of time, the effect of the compressor changing the envelope (shape over time) of the percussive sound can really alter the overall tone.
Using a bus compressor for all the drums is definitely a good idea, it brings them to a whole in very much the same way as using a single-band mastering compressor across the mix. But care must be taken not to push too far. Given the chance, a compressor can really sap the life out of a percussive sound.
In general, excessive amounts of compression in a mix will not translate into a nice master. If a mix has been over-cooked, there’s very little a mastering engineer can do to put things right. Occasionally, expansion has helped in such situations but not very often.
At the opposite end of the scale, I have experienced situations where certain elements in the mix could have really done with some more compression. For instance, dynamic range is not always that favourable with the vocals; at times I find vocals to be under-compressed. A vocal’s expression (loud or soft) is translated through the way the voice sounds and doesn’t need to have huge variation in the actual level. An under-compressed vocal can suffer from certain words or syllables being lost in the mix affecting its intelligibility.
Another aspect that can sometimes be under-compressed is the bass-line. Ideally, the bass needs to be pretty levelled out, at least in its lower regions. The bass-line, along with the beat, make up the foundations of the whole mix and need to be solid. What can sometimes happen is one certain note of the bass-line will jump out, most likely due to some kind of resonance. Or there can be variation in the level of each note down to the way the musician is playing. Don’t be shy when it comes to compressing the bass. Multi-band compression can be useful to focus in on the frequencies that are jumping out.
For most other things in a mix, compression should be used lightly as not to over-cook it. It may be the case that a master can be too dynamic making it unsuitable for playing in a noisy environment, but a good master should still have a healthy amount of dynamic range overall. A piece of music’s expression comes largely from the dynamics of the mix. Squashing out all the dynamic range with excessive amounts of compression will take away the life of the mix. However, there is one situation where being bold with your mixing compression may be more favourable – when you want the final result to be loud. Another chapter covers this in more detail.
Rather than teach you how to mix your music, I have merely pointed out some rules that mixing different sounds together follow down to the way we perceive sound. Mixing is very subjective, heavily dependent on the artist’s taste. In my opinion, a nice mix is well balanced, has good separation, width, depth and punchy dynamics, which is a joint effort of recording and mixing skills. Nice mixes become nice masters, simple as that.