Capturing the energy of live musicians performing in a room together results in a magic that is difficult (if not impossible) to replicate in any other way. The musicians perform better because they can create interactively by responding to one another in real time, and the music seems to take on more of an organic, “live” feel and natural sound that’s ideal for many styles of music. But tracking a band together in the same room sometimes comes with a pitfall — the drums, in particular, tend to bleed or leak into the microphones used to record the other instrument tracks.
Let It Bleed
Before we talk about removing or controlling bleed, let’s talk a bit about bleed itself. Opinions vary on the value of bleed among open microphones on a session — is bleed good or bad? I come down firmly on the side of “yes” when answering that question. To me, bleed can be good or bad, depending on the context, the style of music, the overall production plan and target, and so on. On the positive side, bleed tends to help a recording sound more “live” — as if everyone is in the same room (which they are). This can contribute energy and vibe to a recording and also create a sense of depth in the overall mix. Allowing bleed among mics can have an effect similar to using a room mic to capture ambience in the physical space as the tracks are recorded, but without the “roominess” or reverb factor a room mic brings.
But there can be a dark side to bleed as well. Since the other instruments’ microphones are at varying distances from the drums, there will be time delays as the sound from the drums reaches the other mics. These time delays result in the depth I mentioned above, but delays can also be destructive, in the forms of phase cancellation and “smearing” of transients, as well as potentially muddying up the bottom end.
I think of it as two types of bleed: bleed that contributes to the sense of depth and liveliness versus bleed that corrupts another track. It’s the latter type that I’m most concerned with. I’ll keep as much depth and liveliness in my tracks as I can get!
The Project
I’ve been working on tracks for my forthcoming EP, Foundation. The EP features five instrumental songs, ranging from bluesy rock to horn-fueled funk to straight-ahead jazz. The basic tracks — drums, bass, keyboards (grand piano/Hammond organ with Leslie speaker/electric piano), and scratch guitar — were recorded in Sweetwater’s Studio A in one day with Sweetwater Studios’ Mark Hornsby engineering the session. I played scratch guitar on the session rather than going for “keeper” guitar tracks because I was simultaneously producing the session; my tracks were replaced later with guitar tracks done in my home studio.
The basic tracks feature Keith Carlock on drums, Michael Whittaker on keyboards, and Adam Nitti on bass. Their tracks were recorded live, with the four of us playing in the room at once. The bass guitar was routed through a DI, direct to Pro Tools. The drums and the keyboards were recorded with microphones. The guitar was miked up in an isolation booth, but again, comprised just “temp” tracks played for reference. This resulted in capturing both that “magic-in-a-bottle” energy and some drum bleed into the keyboard mics.
In this video, I’ll take you through my approach and workflow for removing unwanted bleed using the song “Finch Food,” which has bleed from the drums in the organ track. The organ (a gorgeous, pristine, vintage Hammond that lives in Sweetwater Studios’ Studio A) was recorded through a Leslie speaker in an isolation room, with stereo mics on the upper rotating horn and a mono mic on the lower rotating drum. Even though the Leslie was in a booth behind a sliding glass door, some bleed still came through from Keith pounding on the skins, most noticeably kick and snare in the top stereo horn mics, with lesser bleed in the lower mic.
A Caveat
I’ll begin with a warning: be careful not to “over clean” your tracks. It’s tempting to want to remove every trace of bleed from every track, but that can be counterproductive and can even result in damage to your tracks. Honestly, if you want that much isolation among your tracks, then you should record each part separately as an overdub, thus avoiding bleed completely. I recommend taking a conservative approach to audio cleanup — and be sure to compare your “cleaned” tracks with the originals to make sure you aren’t adding nasty artifacts or otherwise damaging the audio that you want to keep. You want to pull back on the bleed just enough to control or reduce any muddiness, “clutter,” or phase issues. My goal is for the tone and vibe of the original recording to remain unchanged, but for the bleed to be removed or reduced. I’ll err on the side of less bleed removal if it means that the sound of the tracks is undamaged.
Stop the Bleeding
With that obligatory caveat out of the way, let’s take a look at a workflow for reducing bleed that works well for me. First, I find both the tracks and the locations in the tracks where the bleed is coming through. This is the point where I assess how damaging the bleed really is; do I feel it is messing with the other tracks in an audible way? Listen carefully with the bleed tracks muted and unmuted. What changes in the overall mix? In my case, I was hearing clutter and muddiness in the low end when the bleed was present; the bottom end opened up and became clearer and tighter when I muted the organ tracks. On examining the organ tracks, I found two problems: drum bleed, but also fairly prominent low-frequency thumping and wind noise from the Leslie speaker itself. These are two separate things, and we’ll deal with each of them.
Once I knew what I wanted to work on, I exported the three organ tracks (top left, top right, and bottom) to my computer’s desktop. The tool I use for the cleanup work is the De-bleed module in iZotope’s amazing RX 6 audio editor/restoration software. The De-bleed module requires two things: the track with the bleed in it (my organ tracks) and the bleed source tracks (the drums).
De-bleed in RX 6 works by comparing a Source Track — in this case, the drums — with a destination track (RX 6 calls it the Active Track), which was the organ track. De-bleed looks for elements that are the same in both tracks and removes them from the Active Track, in this case removing the drums from the organ, while leaving the organ intact. In order for De-bleed to work as well as possible, the Source Track must accurately represent the bleed that was captured on the Active Track, and the Source and Active Tracks must be time aligned. I find preparing the Source Track can require some experimentation, so I exported several versions of the drums from Pro Tools: one with just the gated kick drum, another with just the gated snare drum, a combination of the gated kick and gated snare together on one track, and a stereo submix of the drums with the hi-hat and overhead mics muted.
I loaded the Organ Top and Organ Bottom tracks, as well as the four potential drum source tracks, into RX 6, which was as quick as dragging and dropping the exported audio files from the desktop into RX 6’s window. It was then a simple matter to select either the organ top or bottom tracks as the Active Track and switch among the various drum tracks as the Source Track to find which worked best — in this case, I preferred the results with the kick and snare together.
The Removal Process
Here’s how the De-bleed process works: I started by selecting the Organ Top track tab in RX 6, then opening the De-bleed tool. Next, I selected which Source Track the De-bleed tool should use. In the Active Track, I made a selection in the waveform that contained prominent bleed and told the De-bleed tool in RX 6 to “learn” the Source Track in that selection. (“Learning” tells De-bleed to figure what the bleed is and where it falls.) After De-bleed learns the profile of the selection, you can preview or process the active Organ Top track with that profile.
In the video, after processing, you can hear that De-bleed has pulled down the ambience of the snare, but the overall difference in the level of the bleed isn’t too dramatic. Is it enough of a difference? In this case, I’d like to hear more of a drop in bleed level. When you encounter this situation, here’s a tip: try processing multiple times with the De-bleed tool. In this case, with a second pass through processing, the level of the drum bleed drops dramatically compared to the first pass.
I set the De-bleed module with heavy reduction strength, which really pulled down those hits, but then I turned up Artifact Smoothing, which resulted in less audible artifacts — a cleaner result — from the processing in the final audio. I generally find that this combination of running a cleaner setting multiple times is a great way to get better results than just processing the active track a single time with a very heavy reduction and a low Artifact Smoothing setting.
I then used the exact same workflow on the Organ Bottom track.
Let’s Listen
With the organ tracks cleaned up, it’s time to load them back into Pro Tools and listen to them in context. When comparing the raw (unprocessed) organ tracks with the organ tracks processed with De-bleed in RX 6, the processed tracks are significantly cleaner in terms of bleed. In fact, the bleed has been effectively removed. Check out the difference in the video.
More Cleaning
Though the bleed has been significantly tamed, there’s still bottom-end noise in the organ tracks from the rotors and thumping of the keys, wind noise from the Leslie rotors, and other low-end detritus that is only going to muddy things up in the low end. I really want to clean that out — it doesn’t contribute anything of value to the track, and it clutters up the bottom end and obscures the bass, the kick drum, and the low toms.
There are a number of ways to remove that low-end messiness; in fact, I could have done it in RX 6 using various other modules and tools in the software. In this case, I chose to use two different highpass filters in Pro Tools. The first is a 24dB/octave filter set at 120Hz on the Organ Top track, which filters out anything below 120Hz. The other filter is on the Organ Bottom track and is set to 60Hz. I didn’t want to crank this one up too high in frequency, as that track provides natural bass that shouldn’t be removed; taking out the desired low frequencies in the organ bottom track will change the overall tone of the organ — and I’m trying to maintain the integrity of my tracks while I clean up bleed and noise. Check out the video again; auditioning the processed tracks with the additional highpass filtering shows how much cleaner they are than the raw tracks. I could hear a noticeable difference in the clarity and impact of the low end of the full mix when I compared the mix using the raw organ tracks with the one using the processed organ tracks.
Spic and Span
By taking a careful approach to controlling or removing unwanted bleed (remember, not all bleed is problematic; there’s good bleed, too!) and other noise, you can significantly open up and clarify your mix. Some trial and error may be required to figure out how far to go and exactly how to set everything up, but to me it’s worth it to get the best-sounding tracks and mixes possible!
Get iZotope RX6 software here: https://www.sweetwater.com/store/detail/RX6
To read more about how to use microphone bleed to your advantage, check out our article about Embracing Microphone Bleed.