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Mix Headroom vs. the Mastering Engineer

August 1, 2010

Figure1Fig. 1. Mixes like this are no fun to master, and they can’t be mastered to reach their full potential.

If there’s one thing a mastering engineer doesn’t want to see, it’s a mix that looks more like a sausage than audio (Figure 1). This is usually due to someone who straps a maximizer-type dynamics processor across the master mix bus for a “loud” sound, without realizing that it ties the mastering engineer’s hands (who likely has better tools for making audio loud anyway). However, lately I’ve been getting something more disturbing: mixes that look a lot like Figure 1, but upon closer examination, have clipping issues.



Figure2Fig. 2. The peaks circled in red are clipped.

Referring to Figure 2, you can see the waveforms are “flat-topped,” which causes clipping distortion. One reason this happens is because the mix engineer doesn’t realize that with digital, “going into the red” almost invariably generates clipping, so they don’t get too bothered when the overload light goes on. But another is personal taste: Some people like the sound of digital distortion, and figure a little clipping won’t hurt. But when this file goes to the mastering engineer, remember that mastering puts a sort of magnifying glass up to the audio. Once digital distortion is part of a mix, there’s almost nothing the mastering engineer can do to remove it. The end result is a sort of fuzzy, harsh quality that robs definition and causes ear fatigue.

Figure3Fig. 3. The peaks circled in red have been severely compressed, but still sound better than being clipped.

Now consider Figure 3. This also shows a mix that has virtually no headroom, but it’s due to excessive amounts of compression and limiting, not clipping. The waveform peaks aren’t flat-topped, but simply reduced in level. Although this file is still far from ideal from a mastering standpoint, and won’t let mastering reach its full potential, it’s better than clipping distortion.

Let the Mastering Engineer Master!

The solution is simple: Don’t use any processors across the stereo bus (like maximizers), and set levels so there’s plenty of headroom when mixing—I generally don’t let peaks go much above –10 to –6dB in my mixes. Mastering can always make it loud.

Some engineers balk at this, saying they like to push the output because it’s part of their sound, and they like a squashed effect. In that case, sure, throw a maximizer across the stereo out, and mix away—but bypass it before exporting the final mix. Then include a note to the mastering engineer saying you want a really loud, squashed mix; they’ll do their best to give you what you want.

As a mix engineer, get the mix and the balance right—but don’t mix too hot and introduce distortion, or you’ll just end up with a frustrated mastering engineer, and a recording that won’t sound anywhere near as good as it possibly could when it’s mastered.

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