Mixing in the Box

What’s the truth? I believe that analog and digital, being different technologies, do have different characteristic sounds — so it’s not surprising some people might prefer one over the other. However, while I don’t buy the extreme view that ITB mixing sounds just plain bad, doing a good ITB mix involves some techniques that aren’t relevant with analog. Such as . . .

Realize that recording resolution and audio engine resolution are different. Recording resolutions higher than 24 bits are fictional, due to the limitations of A/D technology. But your sequencer’s audio engine needs far greater resolution (see Jargon Jockey). Today’s sequencers use 32-bit floating point and higher resolutions (all the way up to 64-bit), but many earlier sequencers did not. If you’re mixing ITB with a sequencer that’s a few years old, consider upgrading.

Practice proper gain-staging. Because modern audio engines have so much headroom, it’s almost impossible to get distortion just by mixing channels together. Still, many engineers recommend keeping the master fader close to 0 and adjusting gain within individual channels to prevent overloads at the master out, rather than keeping the channel faders high and reducing the master gain to bring the levels down.

Add steep low-cut filters on mixer channels. Analog consoles rarely had response down to DC, due to the use of coupling capacitors. But digital is capable of creating and reproducing subsonic signals, which take up bandwidth and reduce headroom. Insert a steep low-cut filter, and set its frequency as high as possible (consistent with retaining a full bass sound). Choose a mode of at least 24dB/octave, but some digital filters let you go even steeper. As to frequency, it depends on the material; with bass, maybe 30Hz will do. With voice, maybe 100Hz. Trial and error works best: Raise the frequency until you hear the bass start to diminish, then lower it so you don’t.

Remove DC offset from your tracks before you start to mix. As with subsonics, DC offset reduces headroom. If it’s really bad, you’ll see an asymmetrical waveform in the waveform display. But not all waveforms are symmetrical to begin with. You can just run the “remove DC offset” algorithm to be safe.

Don’t always slam the meters to 0, whether recording or mixing. Digital metering does not necessarily show the true peak signal level, as it measures the samples themselves; interpolation may result in higher values than that of the samples themselves. So, leave a few dB of breathing room for the cleanest sound. (This is less of an issue with higher sample rates, so you might consider “spending” the extra bandwidth to go for 96kHz — and you might also hear better sound quality with plug-ins, particularly distortion-oriented ones like amp simulators.)

Not all plug-ins are created equal. Those EQ plug-ins that come with your host sequencer may be convenient, but specialty plug-ins made for mastering will likely sound better — although they’ll take a bigger hit from your CPU. So what? If you freeze or premix the track, then the CPU consumption won’t matter.

Choose your dither algorithms carefully. Dithering can indeed help a digital signal sound better, but there are two issues. Your host may dither automatically, which you don’t want to do if your mix will be mastered later with a mastering program; and, you’ll often have a choice of dithering algorithms. Their sonic differences may not be obvious, but they can have an almost subconscious influence. To evaluate the sound, take a high quality recording of something like a piano chord that decays to silence, copy the track, and apply different types of dithering. Cut off the note attack until it’s decayed to an extremely low level, where the dithering comes into play. Normalize each example, and you’ll hear the difference more clearly.