Eliminating High-Hat Spill

Blog Header Image: Eliminating High-Hat Spill

When recording a drum kit one of the most perennial problems encountered is high-hat spill on the snare microphone. Some engineers claim to have made peace with this issue by utilising the signal as simply “part of the drum sound”. This doesn’t do it for me since, among other problems, it ruins my stereo image of the kit, placing the hats immovably in the centre. Others aim their microphones such that the null in the cardioid pattern (i.e. the rear of the mic) is directed at the hats. Others even suggest using a figure-8 mic such as a ribbon, which has deeper nulls in its off-axis response, placed so that the side of the capsule looks at the hats.

None of these solutions provide suitable buoyancy to float my little boat. For a start, dynamic mics – especially the SM57 – do not, in my opinion, sufficiently capture the snap and sizzle of a snare drum, and besides, positioning one so that its rear is pointing towards the hats without disturbing the drummer is a tactical nightmare. Ribbon mics are scarcely much better, since there is no one location where the rear of the microphone is not detecting an unworkable amount of the tom behind it. And I don’t even want to think about the consequences of the inevitable battering it is going to take from the drummer. In any case, microphone positioning of this nature when in such close proximity to other undesirable sound sources is purely a hypothetical exercise. In the real world the results achieved by nit-picking in this manner are more or less negligible. The harsh spill from a close set of loud high-hats is simply not going to be significantly reduced by inching a microphone on its axis one way or another.

When I record snare drums I generally like to use the very tiny Shure Beta 98 microphone. It sounds absolutely excellent, gives great top end crack, has very fast transient response, and is so physically small that it can be positioned anywhere around the drum without getting in the drummer’s way (it also has great mounting hardware so as to clamp rigidly onto the side of the drum, thus eliminating the requirement of yet another mic stand). Then when I mix the snare I like to take a good, transparent EQ and make it extremely bright. That’s how to achieve a good crack that pierces like a razor blade though the mix. However, in order for this to work the snare must be as isolated as possible from the rest of the kit, and the high-hat above all must be eliminated as much as possible from the signal, or at the very least its high frequencies significantly reduced.

So. We have a conundrum on our hands. If we can’t budge on mic choice and we can’t solve the problem through placement, the only other alternative is baffling. With this, I set to work.

Now, I have read several times on forums and in textbooks such as Bobby Owsinsky’s “The Recording Engineer’s Handbook” that a good method of baffling ambient sound from a drum mic is to cut a hole in a polystyrene cup, poke your microphone through the middle and then tape the contraption together. Dubious, I gave it a try, suspecting that polystyrene does not present a suitably absorbent or reflective material to deflect close proximity, high intensity sound. As it transpires, I was right. Not only this, but I couldn’t imagine actually putting this into practice in a recording session without feeling like the dickiest of amateur dicks: “We’re all miked up lads… now, get me a paper cup and some gaffer tape!”. However, somewhat inspired by this idea I thought that perhaps I could build a contraption out of a more rigid material, take some steps to furnish it with some proper isolation material and then affix it retractably to the microphone, thus making for a more professional, more effective baffle and thereby solving our problem.

The idea? Tennis balls! One tennis ball, in fact. Cut in half, a hole cut in the middle, the outside covered in tin foil and the inside stuffed with acoustic foam. As I sat in one sunny Saturday, craft materials sprawled everywhere and glitter all over my face, my train of thought pulled in for a long stay at Genius Junction. This, I knew, was the solution to all my high-hat woes. I was indeed a genius. The result looked like this:

Attempted high-hat baffle

I thought it looked pretty smart. But did it work? Well, let me tell you…

No. It was shit. Not only was it absolutely ineffective, it also turned the source, i.e. the snare, into a tonally retarded shadow of its former self. And this makes perfect sense too – if you place a microphone within the confines of a cavity, then the acoustical properties of that immediate boundary are going to wreak havoc on the direct source you are trying to capture. The resonant frequency of that cavity combined with the filtering artefacts incurred by the boundary (the boundary effect) are going to dick with your source sound in a totally undesirable way. To see for yourself, just cut a hole in the bottom of a paper cup and put it up to your ear while listening to some music. Sounds awful, doesn’t it? If more proof were needed, here are the results of my tests:

Snare Test 1: Shure Beta 98, close, no baffle

Snare Test 2: Shure Beta 98, close, tennis ball baffle

So I think we can safely say that forming any kind of cavity immediately around a microphone is definitely not a good idea. This means that we have to find some other non-intrusive way of baffling the high-hats. Since the tennis ball idea not only sounded bad but also did very little to reduce the harsh frequencies of the hats, it seemed to me that we needed to think bigger to think better. I know from experience that an extremely good source of acoustic insulation is Rockwool, due to its high absorption coefficient, especially in the high frequencies – exactly where the harshness of the hats resides. So if we could somehow fashion a non-intrusive baffle out of four inches of Rockwool, then maybe we would be on to something. I immediately got to work on some leftover sound insulation with a Stanley knife. After many hours chopping, changing and inhaling an ever increasing quantity of microfibres, I discovered a solution that created no cavity around the microphone and significantly reduced the harsh top end of the hats in the snare mic. That solution was to raise the hats such that a four inch thick slab of high-hat shaped Rockwool could be installed beneath them, with the snare mic tucked underneath. It wasn’t pretty but it worked a treat:

Rockwool underneath high-hats

For those of you with anxieties about raising high-hats, I should point out that this approach really is the first port of call when attempting to reduce high-hat spill. The further away you can move a source from the microphone, the less intrusive it will be. With the hats this carries the added bonus that it moves the drummer’s point of contact to the less clangy side of the hats, as opposed to the harsher top.

Finally we’re getting somewhere. For good measure, and simply because it seemed like it was something I should do, I added a chunk of acoustic foam underneath the Rockwool, just to see if I could knock off that spill a little more:

Prototype high-hat baffle

The results were excellent. The high-hat spill was becoming reduced to a much more manageable level:

Snare Test 3: Shure Beta 98, close, Rockwool + foam baffle

The only remaining problems now were a) how to make this monstrosity more aesthetically pleasing, and b) how to not disrupt the drummer by its presence. Both of these concerns were addressed by cutting the Rockwool down to exactly the size of the high-hat (generally 14″) and taking one extraordinarily tedious afternoon to assemble a small pair of trousers in which to house it all:

Material for high-hat baffle

The Rockwool was inserted into the black cotton trousers, with the foam glued to the underside. By clipping this to the stand immediately beneath the hats, the microphone can can be tucked discreetly underneath, also then protecting the mic from an accidental battering from the drummer.

And there it is! This is how to eliminate high-hat spill without ruining your snare sound. And it just goes to show – don’t just believe what the textbooks tell you. Try it yourself, and if it doesn’t work, get creative.

High-hats with baffle underneath

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I am James Gasson, music warrior. With my mighty skills of imperfect objectivity and excellent tea making, I am on a mission to encourage critical thinking whilst trying to avoid tripping over stuff. Fancy chatting about audio, drum recording, life, the universe, and/or everything? Drop me a line!

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