Mic bleed: how to prevent it, remove it, and use it in your mix

Ever isolate a vocal and come across an unwelcome instrument in the mix? That, my friend, is mic bleed: sound from one source picked up by a mic meant for another. It isn't always bad. We'll cover when bleed helps and when it hurts, how it happens, how to reduce it while recording, how to remove it in post, and how to use it to your advantage. Let's begin.

Follow along with this tutorial using iZotope RX and Neutron. 

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What is mic bleed?

Mic bleed – also called microphone bleed, spill, or leakage – happens when a mic picks up a source it isn't pointed at. You'll usually run into it in one of four forms:

• Headphone bleed: the click or backing track leaking from a performer's headphones into their mic
• Instrument bleed: a loud instrument picked up by other mics when musicians play in the same room
• Drum bleed: hi-hat and cymbals spilling into the snare, tom, and vocal mics
• Podcast mic bleed: one host's voice picked up by another host's mic

Is mic bleed always bad?

Nope. If it still sounds good with both mics up – your instrument mic and the unintentional one – then it's not bad bleed, it's good bleed. It only becomes a problem when it stops you from editing or processing one source without changing another.

How does mic bleed happen?

A stray source can get into a mic in a few ways.

Headphone bleed

Most notably, bleed can come right through the headphones and into the mic, especially if the performer is tracking alone and likes their headphone feed loud. Singers are the usual suspects here.

Bleed between instruments in the same room

Bleed also happens when several musicians play in the same room. One instrument – say, a piano – can overpower whatever isolation you've set up, like gobos (an acoustic isolation panel) or glass isolation booths. Then the piano leaks into the acoustic bass, drum, or electric guitar mics. Here's a bass track with prominent piano in it:

This can even be intentional, and it can add to the cohesion of a track. I personally love mixing jazz records where bleed is all over the place. With the tools I'll get into shortly, I can make some really creative decisions about how to use that bleed.

Bleed on multi-mic'd instruments

Bleed also shows up on multi-mic'd instruments in a way engineers often hate with the fire of all their being. The prime example is the hi-hat on a drum kit. Steve Albini, blessed be he, once said the hi-hat gets everywhere. He wasn't wrong.

If people are playing in the same room at the same time – particularly at a concert – you're going to get some bleed. The vocal mic will probably have some drums in it. The drum mics will probably have some of the band. It goes with the territory.

Podcast mic bleed

Over in post production, podcasts can have bleed from one host into another's mic, and this too can be exceedingly annoying. It's the same principle as recording a band in one room: put people next to each other, and each mic picks up both of them.

There are things you can do with mic placement, but they often run counter to what the video side of a podcast needs. More on this later. Well, actually, now.

How to prevent mic bleed while recording

If you're lucky enough to be recording the session, you have a chance to fix bleed at the source. Closed-back headphones, polar patterns, isolation panels, and room treatment all help – but each one comes with a catch.

Choose a polar pattern that rejects bleed

Mic placement and selection is important. An omnidirectional mic picks up sound from all directions. A cardioid picks up sound in a heart-shaped pattern: most sensitive at the front, most rejecting at the rear. For the best rejection of sounds you don't want, a figure-8 is your best bet. It picks up audio at the front and back and is very dead on the sides.

Use mic placement to make bleed work for you

Somewhat counterintuitive but true nonetheless: if you learn about the science of wave propagation, you can use mic distance and instrument placement to create phase relationships that accentuate what you want out of a sound. You're aiming for the best sound possible right there in the room, and it frequently takes a while to set up.

A helpful tip: monitor in mono when you mic instruments this way. If each instrument sounds full and clear and lovely through all the mics in mono, you're probably good to go in stereo.

Just keep the clock in mind. A musician who's spent three hours banging on a tom to serve your miking scheme might not be primed to give you their best performance!

How to remove mic bleed in post production

What if you didn't track the session? Start by deciding whether the bleed is actually a problem. Then work from the least invasive fix to the most: time and phase alignment, manual editing, gating, and finally iZotope's machine learning tools.

Method	Best for	Watch out for
Time and phase alignment	Live records, podcasts, multi-mic'd drums	Do this first – gating and EQ can't fix bad phase
Manual editing and strip silence	Toms, podcasts with clear pauses	Tone changes when sources overlap
Gating	Drums, podcasts	Timbre shifts as the gate opens on overlapping sources
RX 12 De-bleed	Vocals, snare, toms, cymbals, guitar, piano	Use the least amount needed to avoid artifacts
RX 12 Dialogue Isolate	Noise and reverb in dialogue	Targets noise, not a second voice
RX 12 Music Rebalance	Bass, full drum submixes	Works on whole sources, not individual mics

Start by telling good bleed from bad bleed

Remember: not all bleed is bad. You might, however, make it bad with downstream processing. It helps to think of the two instruments as one group you work on together. That means busing them to the same group and processing them the same, or using linear-phase EQ on both channels to preserve their phase relationship. Either way, the least amount of processing will do.

Here's an example of bleed between two instruments sounding good:

I can make this bleed sound bad if I mess with one track's EQ:

So, I shouldn't.

Align time and phase

If the bleed between two instruments is making processing a nightmare, experiment with time-aligning or phase-aligning one to the other. You can do it by sight and sound – literally watching the waveforms and dragging one until it looks locked in phase:

You can also use a phase-alignment plugin like the Phase module in Neutron 5. Note how much tighter the snare sounds when I'm done.

For live records, I find this technique to be a crucial starting point. Same for podcasts. All the gating and fancy processing in the world will fall flat if the phase relationships aren't right.

Here's a short video showing the difference phase relationships can make on a mix. It's from a promo video I made last year, but it does the trick.

Edit manually

If you have the time – or it's not too hard to do – simply muting regions where an instrument isn't playing or a podcaster isn't speaking is a great way to go. Many DAWs have a built-in strip silence function you can tune to catch bleed.

Strip Silence in Logic DAW

Do keep in mind, you'll hear a change in sonic character when two of these offending instruments (or people) overlap. No way around that. Personally, I find this method works best on toms.

Use a gate

You can use a single-band or multiband gate to pull bleed out of the sound. The Gate module in Neutron has two really useful presets for post production work.

Neutron 5 preset - Dialogue, multiband gate 

Neutron 5 preset - Dialogue, single band gate

However, you'll still run into issues when the two sounds overlap in time. If one podcast host talks over another, a gate means you'll momentarily hear the timbre of the whole sound change.

Use iZotope's machine learning tools

Now we get to the creme de la creme: iZotope's smart tools for minimizing bleed.

RX 12 De-bleed module

RX 12 De-bleed got a full rebuild with machine learning, and it's astonishingly good. It can pull the snare, toms, or cymbals out of a mic and work on vocals, guitar, and piano – no separate bleed reference track required. I wish I'd had it for some live records I did last year.  

Observe how well it isolates a vocal.

The tech is so good, I can isolate the snare within the vocal. I can even  mute everything but the snare in the vocal with the plugin's Invert Bleed button. 

In podcast mixing, RX's Dialogue Isolate is also quite good. It can really clean up a horrid noise floor while leaving the rest of the material intact.

RX Dialogue Isolate module

Observe this remote interview, treated with Dialogue Isolate.

For sources De-bleed doesn't target – namely bass, or an entire drum kit – you can go in the opposite direction with Music Rebalance, also reworked for RX 12. Here, you solo or bring down the other instruments, as I do on this drum submix. 

How to use mic bleed to your advantage

Don't be afraid to use all these tools together. Here's a method I love for live records: keep the bleed on the main track, where it sounds good, and take it out of your effects.

Say I'm working on a live rock concert recording. I want reverb and delay throws on the singer, plus parallel compression. Small problem: there's significant drum bleed in the singer's mic. Here's how the method works:

1. Phase and time-align the vocal to the drums, so you don't have to gate the vocal. This way the character of the drums doesn't change whenever the singer is singing.
2. Route your vocal to an aux track – or simply copy it and dead patch it (route it to nowhere).
3. Run RX De-bleed on the copy to isolate the vocal.
4. Send that clean copy into a parallel compressor, a reverb, a delay, or anything else.

Now your effects are free from bleed, but your vocal is still using it. That's thinking smart!

Get busy using bleed to your advantage

Now that you have the tools and a little bit of the know-how, you should be well on your way to dealing with mic bleed. Remember: just because there's blood in the name, you need not fear it. Blood is the stuff of life, after all – and the same goes for bleed.

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