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Working With Mic Bleed

Learning To Love Spill
By Wessel Oltheten

Working With Mic Bleed

When you record multiple sources in one room, bleed is inevitable. And, used creatively, bleed can make good recordings even better...

Like many engineers, I like learning about recording history. I enjoy trying to piece together how the great records of the past were made, and considering what lessons I might learn and apply to my own work. And when I'm reading interviews and biographies, I'm struck by how often engineers who cut their recording teeth in the '60s enthuse about the positive qualities of microphone bleed. For many engineers today, that might seem confusing: many of us now view the leakage of sound from one instrument into another's microphone as a problem to be solved. To that end, we've developed myriad ways to isolate sounds and suppress spill. Solutions include: building the record in piecemeal fashion, by recording one track at a time; the old woollen-blanket treatment or the use of more advanced acoustic screens when recording; gates, expanders and other dynamics processors; spectral editing; and, more recently, intelligent 'unmixing' software that analyses frequency components in a recording in order to detangle the whole into its separate source sounds.

Separation Anxiety

But what caused this obsession with isolating sound sources? Why do we feel the need to minimise bleed in the first place? Well, there are a number of valid reasons, listed below.

Controlling The Content: Repairing individual off-key notes is almost impossible when all the other instruments' mics pick up the offending instrument too, and while solving timing issues can be possible [see this month's Session Notes, for example — Ed.], it's often not. Replacing one musician's entire part with a new one is harder still. By contrast, if you record every component in a piece of music in isolation, you're always able to change the content of each recording after the fact. If you lack confidence in the arrangement or the performance, or in your own ability to judge these things while focusing on the technical aspects of a recording, retaining this degree of control for the mix stage can obviously seem appealing.

Controlling The Mix Balance: In any mix, all sources are interdependent. Spill increases the degree of interdependence, and thus makes radical deviations from the acoustical balance of the recording room impossible. If you pursue a sound that's not considered a 'natural' one, you need sources that won't drag other instruments up, down, left or right with them as you ride the faders or tweak the pan pots. For example, a modern metal band cannot sound acoustically the way the producer will intend them to sound on the finished record. So it usually makes good sense to capture 'clean', isolated tracks for further processing and triggering.

Preventing Blurring: Problematic bleed (of which more later) distorts the natural sound and spatial positioning of instruments — the instruments are added to the mix at more than one position in time, due to the different distances from the source to each mic, and this 'blurs' or 'smears' their sound. Comb filtering, masking, loss of perspective, and conflicting or confusing stereo placement can all arise from such problematic bleed.

Coping With Problem Environments: If a recording room is too small or too lively, or if a stage is littered with loud monitor wedges, an engineer might choose to keep the negative outside influences from penetrating the recording by isolating the instruments from their surroundings as much as possible. (Of course this also eradicates any beneficial instrument bleed.)

Keeping Creative Options Open: More and more, pop music in particular is created in smaller studios, with the writing and recording processes often intertwined, and arrangements being tweaked well after mixing has begun. Having individual control over each component is both a consequence of and a precondition for that way of working.

Bleeding Benefits

Still, while there may be obvious reasons to strive for greater isolation, there can be down sides, too. One of these is that (even with the modern pop-style production mentioned above) you lose out on the benefits of the classic approach of first finishing the composition, arrangement and instrumentation of a song, then having a band or artists rehearse the piece, and then recording them playing it together, in one performance.

In my experience, when creating an album of original material with a band, the band usually becomes better at performing those songs once they're well into the promotional tour. Arrangements have matured by then, routines have been built, and individual performance details nailed down. If you record them in that state, all playing together in the same room, you'll often capture something that feels more 'real' than the album. It may lack some of the album's 'polish' and some specific sounds, but if the recording and performance are good, I find that I rely less on production tricks to create a record that sounds striking — to me and to an audience.

Frank Zappa famously assembled some of his records from various live recordings, and he wasn't alone in that. Nowadays, many electronic musicians attract plenty of YouTube views with hybrids of prepared studio production and live performance (check out Binkbeats, for instance: And even if you produce electronic music, performing your work live and recording it in one go can be beneficial — it can certainly provide you with a solid base, hopefully containing some moments of improvised magic, which you can still edit and add to without losing its one-off quality. Such an approach does require some planning of which sources you'll want to record acoustically, of course, but you can be sure your work will sound different, and that it will gain a more 'organic' quality.

Hopefully, I've persuaded you that capturing the energy of a single, unique performance can work well, and is at least worth trying if you've not attempted it before. But if capturing your performance involves using microphones, there's still that small matter of bleed to consider...

When & Why Is Bleed Problematic?

Any sound that doesn't add new information to a mix — in other words, something that is only a slightly out-of-time copy of existing information —has the potential to cause problems. By...

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Published May 2019