A Word About Microphone Bleed
A lot of our usual setup for a tracking session is about isolation, trying to keep the drums from bleeding into the guitar mics, trying to keep the guitars from getting into the vocal mics, and trying to keep the bass from going, well, everywhere. The quest for isolation goes back at least to the early 1970s and has influenced not only the way musicians set up in the studio, but the way we record them.
A Bit of History
Until the mid 1950s recordings were almost exclusively made with all the musicians involved playing live in the room, but our observant readers will note that a small number of recordings were done by playing a track from one tape recorder while playing along, and capturing the result on another tape recorder. One of the most famous examples of this is Chuck Berry’s 1958 Chess recordings, where he overdubbed a second guitar part on songs like “Roll Over Beethoven.” It wasn’t uncommon to record a group with no microphones designated specifically for the drums. At a 2001 Audio Engineering Society seminar, legendary engineer Bruce Swedien talked about a session he conducted with the Count Basie Orchestra, with vocalist Big Joe Williams in 1959. Swedien used eight microphones, one each for piano, rhythm guitar, upright bass, and lead vocals, with the other four mics used to capture the rest of the orchestra. Was there bleed? You bet. None of the microphones were capturing a single instrument, not even the vocal mic. Nevertheless, the recording sounds stellar.
While mic bleed was part of the sound of those iconic records, it wasn’t considered to be either a problem or an advantage — it was simply what happened. Even into the 1960s and 1970s, the normal way to record music was with everyone playing at the same time. Bleed between instruments was controlled by placing the musicians in the right part of the studio, with the use of gobos (https://www.sweetwater.com/store/detail/GoTrapBk–primacoustic-gotrap-studio-black), with microphone choice, and with microphone placement. The goal, however, was not to eliminate bleed and isolate each instrument — rather, it was to control the levels of the individual instruments in the mix. The engineers at the time weren’t concerned about whether the guitar amp was bleeding into the drum mics — they simply wanted to make sure the guitar wasn’t louder in the drum mics than the drums — and vice-versa.
At some point in the transition from “live in the studio” recording to the current state-of-the-art setup — which essentially means an unlimited number of tracks — the ability to build songs one track at a time, the ability to record the same part many times and choose the best take (or edit many takes together into the final part), meant that the performances recorded together might not be the performances that made it to the final mix. And while there are classic 1960s and 1970s recordings where some instruments’ earlier performances are audible in the final mix (because they bled into some other instrument’s mic that wasn’t replaced), it quickly became unacceptable to artists, engineers, and producers in many styles of music. One reason may have been that recording practices which worked well when drummers played fairly quietly, when bassists used Ampeg B15s, and guitarists used a Fender Princeton or Deluxe didn’t work nearly as well when 100 watt Marshall Super Leads, 300 watt bass amps, and drummers like Carmine Appice and John Bonham came into the studio. At those kinds of volume levels, what were once acceptable levels of bleed often became uncontrollable.
The desire to eliminate bleed eventually led to the wide-spread use of isolation booths, the use of DIs on bass instead of having the bassist play through an amp, and the practice of recording instruments one at a time — or at least, having the band play together and then replacing each instrument separately. This also led to some moments of pure silliness, like engineers who would record a drum set one drum at a time, so that there was no bleed between any of the drum tracks.
But here’s the thing about microphone bleed — as long as (A) the sound of ALL tracks together sounds great, and (B) there are no mistakes that have to be fixed on individual tracks, bleed isn’t a problem. If you solo the electric guitar track and you hear a bit of the drums, so what? You’re the only person who will hear that guitar track in isolation — the rest of the world will hear it as part of the final mix. If the guitar amp is bleeding a bit into the bass amp track, but both the bass and the guitar sound great in the final mix, there’s not a problem.
Over the years, I’ve recorded a lot of singers who play guitar or piano and want to play and sing at the same time. I’m fine with whatever allows the artist to give their best performance, but despite our best efforts, there is likely to be a bit of the instrument in the vocal mic, and a bit of the vocals in the instrument mic. When mixing this sort of performance, the main thing to remember is that any processing done to either the vocal or the instrument track (compression, equalization, reverb, or delay) will have some effect on both the vocal and the instrument. So, don’t make processing decisions in isolation – do them while listening to the whole mix.
There are some situations where this kind of bleed can be a problem, but they’re pretty specific. One is when something needs to be fixed on one of the tracks but not the other, like a wrong chord in an otherwise fine performance, or a mis-sung lyric. Even though only one of the tracks has an issue, the easiest way to fix it is to have the artist play and sing that section again. Another is when the instrument drowns out the voice in the vocal mic (which occasionally happens with artists who play loudly but sing softly). This issue can usually be minimized with the use of baffles, directional microphones, and some coaching from the control room. Yet another is when the vocals have to be tuned and the instrument is bleeding into the vocal mic. If that’s the case, I’ll have the singer sing separately from their playing — even if they’re a bit uncomfortable working that way.
Ultimately, microphone bleed is neither good nor bad — it’s simply the result of having more than one instrument in the room, playing through more than one microphone. Recordings can sound great with all the instruments being completely isolated, and they can sound great with the instruments bleeding across multiple tracks.