You are here

Compressing Your Mix

Tips & Techniques By Paul White
Published December 1994

Paul White proves once again that nothing succeeds like excess. This time he patches in two compressors and a limiter to deal with a minor dynamic range problem...

I presided over a session recently where the client brought back an album production DAT of pop songs I'd compiled for them, because they were worried that the music didn't sound loud enough when compared with commercial recordings. It wasn't simply a matter of increasing the level on tape, because the peaks were coming within 3dB of digital clipping — it was, of course, a matter of dynamic range. In other words, their loudest bits were as loud anyone else's loudest bits, but the average level of the material was well below that you'd expect from a commercial album of similar material. You might imagine that dynamic range would be no problem, as everyone has a compressor in their studio — but in practice, a great many recordings are compressed on an individual track basis, with more compression being added to the overall mix.

If you know that you are going to compress the overall mix, it makes sense to patch in the compressor at the outset, so that you can hear the effects of the compressor if you mix. The reason behind this is that compression can change the subjective balance of a mix, so if you finish your mix before thinking about compression, you could end up with problems. However, this is exactly the situation I was confronted with — a completed DAT tape that could obviously only be saved by being compressed. I turned to my Drawmer rack, although the methods outlined here could be put into practice using virtually any reputable compressor — so don't stop reading if you're not a Drawmer fan.

I decided that the 1960 valve compressor would be a good starting point, because it is a soft‑knee compressor, which makes it less obtrusive in operation than a fixed‑ratio type. As a bonus, the valve circuitry also adds a touch of magic to the sound, but you could use any decent soft‑knee compressor. Using a fast attack and a relatively slow release time (around 2S, at a guess), I set the threshold to produce around 6dB of gain reduction on the signal peaks. This isn't a great deal of reduction, but then I didn't want the signal to sound too squashed.

Soft‑knee compressors may be unobtrusive, but what they offer in subtlety, they lose out in assertiveness, and occasionally a peak comes crashing by that they don't stamp on nearly firmly enough. To solve this problem, I patched in a second compressor, with a ratio of 10:1, set to Auto attack and release mode. You could use either another soft‑knee compressor (so long as it has a variable ratio), or even a standard hard‑knee device here, and if you only have a manual drive model, go for a fast attack and half a second or so release. The threshold was adjusted to produce about 4dB of additional gain reduction on the signal peaks.

A final line of defence came in the form of the DL241's limiter, which is definitely of the 'Thou shalt not pass' variety, and by deliberately driving the limiter so that it was permanently on, I could easily set the recording level on the target DAT machine to fractionally under full scale. Once this was set, the compressor gain was reset so that the peak LED only flashed briefly on the very loudest signal peaks I could find. In theory, the limiter shouldn't have to do anything, but I wanted it there just to make sure that the DAT could never go into overload. Pausing to check that both compressors were set for stereo link operation, I set about copying the original DAT to a new tape. Because this was a compiled album with pauses, I could have used the 241's expander gate to keep the pauses noise‑free, but as it turned out this wasn't necessary, as the compiled master tape had absolute silence in the gaps anyway, so compressor noise wasn't a problem.

The result was better than I could have hoped for; there was none of the dulling of transients that can occur when a single compressor is used to heavily compress a mix, and there was no pumping, yet the mix felt more solid, more cohesive and more confident than the original. Apart from applying less than half a dB of EQ cut at 4kHz, to tame a little vocal sibilance, no further processing was needed, and the clients were relieved that their tape could go on to the CD pressing plant without further delay.

This is just a one‑page article, so I've got to sign off before I collide with the page logo, but do give this a go — you might be surprised at how much more punchy and together your mixes sound.

Choosing Your Weapons

I put the success of this operation down, not only to the quality of the compressors used, but also to the use of two separate stages of compression backed up by a 'watchdog' limiter. The first compressor provided the bulk of the gain reduction, and so had to be unobtrusive, which is why a soft‑knee model was chosen. The second model comes in only to deal with peaks that the first compressor fails to bring under control, so you can afford to be a bit more heavy‑handed. Again, either a soft‑ or hard‑knee compressor can be employed, though the type with a variable ratio works best.

While this combination of compressors works fairly transparently, the same can't usually be said of limiters, so it is imperative that the limiter is set to cut in rarely, if ever — it's simply there as a last resort.