Feature/Interview

ADVICE: Sound Reasoning Part 5 – leakage

Mark Wingfield is a mixing and mastering engineer at Heron Island Studio. He has three DownBeat Masterpiece albums under his belt, a Jazzwise Best Release Of The Year, and over 300 rave reviews from around the world for albums he has worked on. In this series of articles Mark gives advice on how to avoid common mistakes made in the recording studio which will hold back your album from sounding great.

Most jazz is recorded in small studios (Photo: Borislav Kresojević)

Leakage 

I talked a bit about leakage in the second piece about microphones (Part 4 in this series), but there’s more to it than mic placement. Leakage – when the microphone of one instrument picks up other nearby instruments – is something I see all the time with recordings in small rooms. It can also be referred to as microphone spill. It’s typically less of a problem in large rooms, but it can ruin a recording in small studios.

In the right room, some spill is a good thing. If a room allows a good space between the musicians and the sound bounces back and reverberates into all the mics, it can create a beautiful blend of the room and all the instruments. However, rooms that do this naturally are rare. Most are the result of careful acoustic design. They also need to be fairly large. Realistically, such spaces cost too much for most jazz musicians.

How about recording in a church or similar large hall? That might sound good if you were recording a choir, but there will probably be far too much reverberation for recording fast tempo jazz. A space for jazz needs a fine balance of just the right amount of reverberation, at just the right frequencies. Finding your own large space to set up for recording is problematic. You also need a good engineer. Capturing the sound of a great room takes a lot of skill.

Most jazz, I would venture a guess of around 95% these days, is recorded in small studios. No small room will sound very good in its natural state because of flutter echoes, phase cancellation, standing waves and other resonation issues. Small studios use baffling and traps to stop or minimise these. The result is a recording with very little ambience. Reverb is then added during the mix to create a great sounding space. You can get a world class sound in a small studio, but you do have to record it the right way and you need a world class reverb when mixing. Of course getting a big, open and detailed sound from a small room is not just a matter of throwing a reverb (however good) on the mix, there’s a lot more to it than that, but this is a subject for another article

In such rooms there is no advantage to having microphone spill. In fact it can be a significant disadvantage. Because the rooms are small, instruments in the same room are close to each other and this requires some care. For example having the piano and acoustic bass together in the same room will cause a problem if you are not careful. You could easily end up with a situation where there is so much piano coming through the bass microphones that you can’t EQ the bass or the piano effectively. You might find that in the mix the bass could really benefit from bringing out the upper mid frequencies so that you can hear the singing tone of the instrument. However if there is too much leakage, when you bring up these frequencies on the bass, you will also emphasis them on the piano. This is unlikely to flatter the piano sound. The result will be that you are unable to get as good a bass sound as you would have if there had been less leakage. EQ aside, the sound of the piano coming through the bass microphone, is not going to be a nice piano sound and will not contain any nice room ambience, so will not enhance either instrument.

How to minimise leakage

Leakage is unavoidable with more than one instrument in the same room. The goal is to keep it low enough to allow a good mix. The first thing of course is to separate everything as much as possible.  The drums definitely need a separate room in a small studio. If you have piano try to give it its own room too. Put the acoustic bass in the control room. Reeds and horns are also better off in their own room even a makeshift room built out of dividers and baffling. Be wary of putting a reed in a small room unless the baffling makes the room really dead. Small room ambience can ruin the sound of a sax. Of course, you will have a limited number of rooms, so there will be compromises. If you need to put two instruments together in a small room, the best choice is piano and bass. However this paring can still easily be problematic. Unless there is sufficient distance between the instruments and the mics are carefully placed, the piano leakage into the bass recording may cause problems at mix time.

Any studio worth using will be acoustically treated (Photo: Borislav Kresojević)

Keep instruments as far away from the walls as possible. Any studio worth using will be acoustically treated. However few small studios have good enough treatment to allow instruments to be near the walls. Without high end acoustic treatment (not just foam on the walls or the occasional small acoustic panel), an instrument too close to a wall – especially a sax or trumpet – will produce noticeable wall reflections and possibly also comb filtering. Both adversely colour the sound. In the raw mix one instrument will sound like it’s in a different room from the rest of the band. It may have a thin or nasal like sound. Or you may end up with noticeable flutter echo or unevenly resonating tones. Flutter echo and small room resonance are things which will prevent the recording from ever sounding great, even if it’s well mixed.

Once the instruments are placed, keep the mics as close as possible to each one. This minimises leakage and reflections, but a mic too close to an instrument may not give you the best tone. So you often need to split the difference. The choice of mic is also crucial. A skilled engineer will be able to find the right combination, but it is really worth being involved in listening to the leakage and reflections being picked up by each mic.

Listening tests

When you have done a test recording of the band, go into the control room and ask the engineer to play each instrument on its own. How much of other instruments  can you hear through each mic? You want other instruments quiet and distant even if they are in the same room, while the target instrument sounds as full, rich and natural as possible. Ask the engineer to adjust the mics (repositioning, or changing the type) until you get the best balance between instrument tone and minimised leakage. This might be time consuming, but it’s so important it is worth hiring the studio for an extra day or half a day to get it right, if your budget permits. If not, then turning up with a clear idea of the steps I’ve laid out in this series will go a long way towards helping you get a good sound.

Mark Wingfield, Mixing and mastering engineer at Heron Island Studio
contact@heronislandstudio.co.uk
heronislandstudio.co.uk

LINKS TO PREVIEWS SOUND REASONING ARTICLES:

Part 1 – the set up
Part 2 – monitoring levels and listening
Part 3 – choosing microphones for jazz recording
Part 4 – choosing microphones, contd.

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