Tag Archives: recording

Comb Filtering In Drum Overhead Microphones

Recording drums in a small room is a problem that any engineer not blessed with an infinite budget must deal with at some point. Among the difficulties inherent in this scenario is the problem of comb filtering in the audio signal due to the microphone’s proximity to a boundary, i.e. the ceiling or a nearby wall. For example, if a singer sang into an omni-directional microphone placed 1 metre from a reflective wall or surface, the sound of their voice would hit the mic but also carry on past it, hit the wall, rebounding back and re-entering the mic about 6 milliseconds after the direct signal.

boundary

 

This is exactly the right amount of time for the frequency components around 85-86Hz to come back close to 180° out of phase with the direct signal. There will not be total cancellation, since the rebounded signal will be weaker and because the sonic characteristics of the singer’s voice are constantly changing, but the effect may still be significant.

frequencies

 

Rounding down to 85Hz, at 170Hz the reflection will come back in phase and reinforce the 170Hz components within the direct signal. At 255Hz it will be out of phase again, and at 425Hz and 595Hz, and at intervals of 170Hz all the way up the frequency spectrum. This is known as “comb filtering”, due to the regular series of peaks and notches across the spectrum. It sounds phasey and generally undesirable.

This effect is demonstrated in this video, where a drum overhead microphone is moved towards a nearby boundary and back again. The comb filtering artefacts are clearly audible in the recorded signal. The first microphone – a Royer R121 ribbon mic – clearly suffers from this effect with great prominence given it’s bi-directional polar pattern, and thus greater susceptibility to rear reflections. The second mic – an Audio Technica ATM450 – reveals itself to be less harshly affected due to its cardioid polar pattern. This then demonstrates the importance of microphone selection with regard to its placement within a recording environment, as well as the importance of placing the mic as far from boundaries as possible, or, when this is not feasible, treating nearby surfaces with good quality acoustic absorption in order to eliminate as many reflections as possible. A combination of absorption and diffusion is most effective.

 

Many thanks to my beautiful assistant, Bebe Bentley, for helping me with these tests. Check out her excellent work in film and moving image on her Vimeo page.

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Binaural Recording

Have you ever wondered how it is possible for the human brain to so accurately detect the location of a perceived sound? We only have two ears, yet somehow we are able to discern the differences between sounds originating from any direction within our 3-dimensional environment – in front, behind, above, below, left or right. How is this possible? And can we therefore simulate this effect in order to artificially reproduce the experience of perceived 3-dimensional sounds, as opposed to the normal left/right experience we are accustomed to in traditional stereophonic speaker set-ups, without simply adding extra speakers?

The answer is yes we can. Directional perception of sound occurs by our brain’s ability to decode the subtle differences in information received by our in-built stereo receivers – our left and right ears. Binaural recording is a recording technique that uses two microphones to mimic the human auditory system, utilising the exact same conditions that create the phenomenon of binaural localisation in humans. And so, with the acquisition of a pair of binaural microphones, a portable Tascam field recorder and a dummy head named John, film maker Bebe Bentley and I spent one evening carrying out some binaural recording tests at the University of Sussex. Here are the results (please note that headphones must be worn in order to perceive the effect):

#1: Binaural recording in a dead room.

#2: Binaural recording in a live room.

#3: Binaural recording of James with a guitar.

NEW-2NEW 1 NEW-4

In the directional perception of sound there are two phenomena at work: Binaural and monaural localisation:

Binaural Localisation

Binaural Localisation refers to the discrepancies in the characteristics of a sound wave arriving at the closest ear, and then the farthest. Your brain is sensitive to the discreet time difference between a sound hitting the nearest ear and the farthest ear – referred to as the Inter-aural Time Difference (ITD) – as well as the slight change in volume between the two ears – the Inter-aural Intensity Difference (IID). If sound originates to your left, your head acts as a barrier or filter and reduces the level of sound heard in the right ear.

Monaural Localisation

Monaural localisation mostly depends on the filtering effects of physical structures. In the human auditory system, these external filters include the head, shoulders, torso, and outer ear or “pinna”, and can be summarized as the head-related transfer function. Sounds are frequency filtered specifically depending on the angle at which they strike the various external filters.

binaural
Binaural recording of the kind Bebe and I carried out works by the use of two omni-directional microphones fitted to a dummy head, thereby simulating as realistically as possible the actual physical location of the human ears, combined with the filtering incurred by the human head. The same effect would be achieved by placing the microphones in your own ears, which would make for an interesting audio experience were you to then simply walk around an urban environment or visit a concert. In these instances it would be possible to accurately record exactly what you heard in these situations, complete with directional perception of the ambient noise, in order to later recreate that exact sensation through a pair of headphones. This, however, is perhaps a test for another day. Here we simply affixed the microphones into John’s ears and proceeded to move objects around and make various noises such that the illusion of directional perception is created.

It is however important, for the effect to be fully realised, that headphones are worn. This is because, on replay, the left ear must receive only the signal recorded by the left microphone, and the right ear only the signal from the right microphone. Playback through speakers destroys this effect by obscuring the stereo field emitted by the left and right speakers.

What strikes me as odd about the experience of listening to this recording is the realism it invokes. When hearing Bebe and I running around the room it is as if ghost figures are appearing in front of you. With your eyes closed you can almost “see” the people. This demonstrates just how unaware we are of the subtleties of our sensory information in building our picture of the world. The next time someone supposes some supernatural bullshit to describe how they “felt a presence in the room”, remind them how easily our senses can be fooled.

So there we are. Artificial directional perception by binaural recording. Now, if only I could find a practical application…


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:

Tennis Ball

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

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:

Rockwool + foam

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:

Trousers

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.

hats


Drum Miking Techniques

While working as a freelance engineer in a prominent Brighton studio I saw that here lay an excellent opportunity to properly exploit a decent live room and a large selection of microphones (a combination of ribbon mics with my own extensive set of small diaphragm condensers) in order to once and for all produce the kind of drum sound that provokes wet dreams in any fan of Steve Albini, and probably be the only studio in Brighton with the foresight to do so. With that notion, and with the promise of a kick drum sound capable of producing an internal haemorrhage elusively wafting through the air, I set to work in order to discover exactly how it is done, and exactly which mics and techniques are appropriate to induce such biological phenomena in a laborious weekend of tedious excitement. Aided by fellow engineer Chris Blakey, and musician and professional cable winder Genti Aliaj, these were our findings.

 
 

The Approach

All tests were conducted through a Neve 5316 using the console preamps, recorded to Pro Tools 9 HD at 96 KHz, 24 bit, and monitored through NS-10Ms and KRK VXT6s.

In order that the best drum sound could be obtained, the approach was logical and methodical:

  1. Get a decent sounding drum kit.
  2. Tune and dampen it as appropriate.
  3. Create a deadened environment using a surround of acoustic screens.
  4. Set up one drum at a time within this dead space and find the appropriate microphone and position.
  5. Reassemble the kit using the close mic techniques found.
  6. Listen for spill and reposition microphones accordingly, without compromising the sound.
  7. Test overhead microphones and positions.
  8. Test M/S microphone and positions.
  9. Test ambient microphones and positions.
  10. Experiment with processing.

It seemed to me that with two days meticulously analysing the drum kit in this way, it should become apparent exactly which microphones are more fit for task than others, and what techniques add to or detract from the overall sound.

 
 

Snare Drum

The snare drum was set within the screen and a selection of microphones aimed at it, in order to approximate recommended techniques suggested by various engineers over the years who may or may not have engaged in this kind of direct comparison. In total 8 mics were used, with diaphragms aligned as closely as possible, each pointing fairly flat against the drum head, around 1½ inches from it. This position seems logical, since aligning the diaphragm parallel to the drum head allows the greatest frequency energy of the drum as a resonating system to drive the diaphragm of the microphone, without passing obliquely across it, as is the case in a non-parallel placement. Indeed, adjustments to this end found that aiming the microphone at the point of stick contact, whilst possibly capturing fractionally more attack, does seem to incur a slight bass roll-off, which is a particular concern with condenser mics where this content is particularly important (since their sound is very different to the dry, bone-headed “thump” delivered by a dynamic).

During the test, each mic was analysed relative to the others for its particular qualities and ranked in order of “likeability”, based on its character and its frequency content. The results were as follows:

Microphone  Rank Comments
Shure Beta 98 1 Bright, full bodied sound. Very directional but with an impressive amount of high end detail and a surprisingly thuddy bottom end. Everybody’s favourite by a long way. Its small size and gooseneck clip also makes it excellent for positioning.
Audio Technica ATM450 2 Another bright mic, although lacking a little of the detail and body of the Beta 98. Still a very good mic but may work better in combination with a dynamic mic to reproduce the depth of the drum (the Beyerdynamic M201 is an excellent dynamic microphone but unfortunately one was not available today).
AKG C414 3 A good, rich, unimposing tone, although with less “wow” factor than the aforementioned microphones. However, its physical size and cost render it probably inappropriate for all except the most affluent of engineers.
Josephson E22 4 The darling of Electrical Audio. A surprisingly dark sounding small diaphragm condenser microphone – its advantage is its rigidity and its directionality, however its top end response seemed to leave something to be desired.
Shure SM7 5 The brightest of the dynamic mics used, but still ranking below all condensers in terms of overall detail. Again, its physical size makes for problematic application in a real world scenario.
Shure SM57 6 Peculiar sounding dynamic microphone that has somehow found its way into the recording aether as a “workhorse” multi-application standard. In this test the SM57 ranks far below every other microphone so far discussed, with a very boxy, artificial sound that carries no discernible benefit other than the fact that you can happily throw it at a wall and find it still sounds the same.
Shure Beta 57 7 Even worse than the SM57, this microphone imparts a very noticeable high mid boost that forces its own character upon the source sound, producing a Frankenstein reproduction of a sound that could never exist in nature. A very poor mic.
Electrovoice RE20 8 This microphone ranks lowest only in as much as it was simply tried as a “bit of fun”. Dark, lacking in high end, physically large and intrusive, and expensive, this microphone is completely and utterly inappropriate for this application in every conceivable way.

The individual recordings of this test can be found here.

With the most appropriate top-of-snare microphone now established, the next job was to determine the bottom mic. It therefore stood that in order to determine this, the designated top mic – of which we had only one – should remain on top whilst bottom microphones were tried in conjunction with it, in order that we could assess which complimented the top mic the best. We tested 7 microphones at the bottom of the snare, each time inverting the polarity (not phase – if you are of the school who think that phase and polarity are interchangeable terms then shame on you, and I will shortly be having words with your mother) so as to properly manage the conditions inherent in two microphones at close range pointing at each other. Taking a small moment to elaborate on this, because the bottom microphone receives the vibrations from the resonating drum head 180° out of phase with the top mic, either one of the corresponding channels should be polarity inversed, thereby adding further definition to the sound of the drum whilst avoiding low frequency cancellation, and also serving to cancel out any extraneous environment noise (like traffic or bass amps), since such noise arrives at the two microphones more or less simultaneously. This is known as a differential principle.

Here are the results of that test:

Microphone  Rank Comments
AKG C414 1 Surprisingly complimentary sound with great separation and nice, rich body, rendering the overall drum sound extra punchy. A good range all round with a top end that is not too harsh. Very easy to place underneath the snare so physical limitations are no issue. Easily the best choice.
Audio Technica ATM450 2 Nice and bright (which is what you want in a bottom-of-snare mic) with a fast response, but lacking the depth of the C414. Still provides a good deal of snap.
Josephson E22 3 A slightly darker, slightly drier version of the ATM450. A good mic but not first choice in this application.
Shure SM7 4 Spits out a pleasant thump but lacks the top end detail of the aforementioned mics. Sounds as you might expect a dynamic mic under a snare to sound.
Sennheiser 441 5 Slightly richer than the SM7 but lacking in top end, rendering it fairly uncomplimentary to the top mic in this application.
Shure SM57 6 Characteristically dry, nondescript sound, not really useful for anything. Less thumping than you might expect and exhibiting extremely poor top end clarity.
Shure Beta 57 7 Entirely ridiculous. All artificial mid-range and nothing else. Sounds like a mechanical sneeze.

The individual recordings of this test can be found here.

 
 

Rack Tom

Although the microphone positioning in this case was based on identical principles as on the snare drum, the analytical process for the rack tom was slightly different, because essentially the mic that is fit for purpose on the top of the drum should also be fit for the bottom, given that the source is more or less the same:

Microphone  Rank Comments
Josephson E22 1 This is where this mic comes into its own. Great attack and full body, nicely preserving the detail of the drum. The darker tone serves to enhance the tom sound very nicely without accentuating any irritating wolf tones.
AKG C414 2 Another nice, rich sound, with slightly less attack than the E22, but still pleasantly full-bodied. However, again it is physically intrusive and makes a great target for a drum stick.
Audio Technica ATM450 3 Slightly less body but good attack. Still a nice clean sound, but possibly not the first choice should an abundance of E22s be available. Having said that, there is absolutely not £500 worth of difference between this mic and the E22, and given its price, small profile and excellent position-ability, this is a great little microphone.
Sennheiser 441 4 A bone-head dynamic sound – nondescript and characterless, but “gets the job done”, if what you are looking for is the lower mid thump without concern for detail.
Shure SM7 5 More attack and less body than the 441. It’s passable, but it would be a strange engineer who considers this an appropriate microphone for any drum.
Shure Beta 98 6 All attack and no body. Strange, because it sounded so rich on the snare drum, but for a rack tom, this mic lacks the required depth to sufficiently reproduce the desired boom.
Shure SM57 7 Sounds like an SM57 – dull and lacking any redeeming features other than there tends to be lots of them about.
Shure Beta 57 8 Quickly becoming the stupidest sounding microphone. More imposing mid-range nothingness and entirely inappropriate for use on a drum kit, or, I suspect, anywhere else.

All in all, the E22 was clearly the most appropriate microphone for the rack tom, however, given their price at around £700, the likelihood of owning enough of them with which to entirely coat a drum kit is very small, unless you happen to be the man who conceived the design. We were lucky to have one to try out, but given the price difference of around £500, there is nothing whatsoever wrong with using the ATM450, which is lucky for us because we have an abundance of them. Where the E22 really scores points however is in its robust design and (as we were to discover later) its superior directionality, meaning that spill from the rest of the kit is less of an issue. However, the ATM450 has pretty good off-axis response, meaning that, even though it does pick up the rest of the kit more than the E22, it never actually sounds bad. Just be careful that your drummer doesn’t smack it with her stick.

The individual recordings of this test can be found here.

 
 

Floor Tom

It is probably unsurprising that the floor tom test harboured almost identical results to the rack tom test, save for some inconsequential ambiguity regarding whether the ATM450 was actually better than the C414 this time around. Either way, It’s pretty clear by now that if you are financially privileged enough to own enough E22s, this would almost certainly be the tom mic of choice, otherwise the ATM450 comes a close second. Either way I believe that you are going to end up with a close drum sound that boasts superior depth and clarity to the standard practice of using only dynamic microphones on the top heads.

The individual recordings of this test can be found here.

 
 

Kick Drum

When we came to examine the kick drum it was quickly established that the position of the mic had more bearing on the sound than the mic that was used. While every mic exhibited its own character, each of which could potentially be useful in different applications dependant on the style of music, the positioning harboured radically different results. Firstly, here is a brief analysis of the four mics tested at the hole of the kick drum:

Microphone  Rank Comments
Electrovoice RE20 1 A great, full bodied microphone that really highlights the accompanying “boom” of the drum, as well as the attack sound. However a great deal of gain is required to produce suitable performance from the mic, and therefore decent preamps are advised that are suitable for the task.
AKG D112 2 Toppier than the RE20, it is actually a matter of preference which one you may decide to go for, with equally good attack and a mid-range that sounds… just… different to the RE20.
Audix D6 3 Apparently designed as a “metal” kick microphone, and you can definitely hear it, emphasising as it does the clicky attack that is a staple of irritating metal music everywhere.
Shure Beta 52 4 Not dissimilar to the D6, it only ranks lower because its physical shape renders it slightly harder to position.

The problem, however, was that, in the regular placement – just at the sound hole at the point where the greatest volume of air is being ejected from the drum – all of these microphones sounded peculiarly plasticky and weird. When listening to the drum in the room it sounded large and booming and just as you would hope a kick drum would sound, but under the microscope this was not the case. In order to remedy the situation, an AKG C414 was slowly moved around the outside of the repeatedly pounded kick drum while we determined to find the sweet spot at which the non-plasticky boom could be sufficiently captured. This transpired to be around 2 feet in front of the sound hole, where this microphone was subsequently positioned. This did bring to mind the idea that I now recalled from other engineers, that a condenser mic outside of the kick drum could sound quite nice, and here we seemed to have confirmed it. It had lots of attack and lots of boom, but the only component potentially missing was some extreme bottom end. Use of a Yamaha Sub Kick right against the resonant head seemed to provide the thud we were looking for, and when compared to the C414 with artificially boosted low end, it resulted in a much more natural sound.

An important component of a good kick drum sound however, and one that is almost always overlooked and then attempted to be fixed at the mix stage (usually by boosting somewhere around the 1-3 KHz mark) is the attack. It is this that is clearly audible in recordings, not the sub. The sub is something you feel, but the attack is something you hear. This is an important distinction to make, because I have seen many people (myself included, some years ago) trying in vain to boost the sub part of the kick drum, ever wondering why they are not able to allow it any definition through the sub frequencies of the rest of the mix. We all know the feeling of the bottom half of our mixes turning into a definition-less squelchy mulch of non-descript boom, without ever really being able to tell what is happening down there. And so the solution to this is to take care to faithfully capture the attack component of the kick drum by separately miking it. The bottom end of this signal can then be rolled off in order to achieve a piercing beater slap that accentuates the kick sound without ever having to boost silly frequencies in the mix. Obviously for this application a suitable microphone is any that has good high end definition but is also easy to place in such an awkward position. Three mics were tried in our test:

Microphone  Rank Comments
Audio Technica ATM450 1 Great attack and full bodied, plus physically small. Combined with an Audix D-Clamp mounting clip, this is very easy to manoeuvre into a very close position. Just be sure it doesn’t get thudded by the beater. That wouldn’t be good.
Shure Beta 98 2 Excellent attack but lacking definition lower down in the spectrum. Also comes with a clip that looks like it is purpose built for this exact application, but after some frustrating fiddling you find that it really isn’t.
Sennheiser MD421 3 Boring dynamic nothing-special microphone that did nothing special in this application except got in the way.

The individual recordings of these tests can be found here.

 
 

Assembling The Kit

Having determined the best microphones and relative positioning, the kit was assembled and all techniques applied with a view to checking how spill from the rest of the kit affected our choices. Happily, spill was hardly an issue, and in fact the benefit of dual miking drums was further accentuated in this regard, as having two microphones in different locations pointing at a single drum serves to enhance the character and definition of that drum whilst cancelling spill from elsewhere in the kit, or at least widening the relative signal-to-noise ratio. I suspect that this is therefore a critical consideration in using condenser microphones as close mics on a drum kit because, although sonically superior to dynamics, the advantage of dynamic mics is their off-axis rejection and poor high frequency response, meaning that crashing and clattering cymbals from elsewhere on the kit tend to interfere less with the dull character of the dynamic microphone. Therefore, as a rule of thumb, for excellent drum definition with condensers, use two of them.

The only instance in which spill was a noticeable concern was with the C414 in front of the kick drum, which by now was reproducing less of the boom exhibited by a single kick drum being repeatedly and consistently struck on its own, and more of the cymbal clatter from the rest of the kit. It had lost definition, and it was apparent that a closer technique was required in order to produce acceptable separation. It quickly became clear that a sound hole microphone could actually be used, so long as it was angled in such a way as to minimise the plastic tone of the beater slapping against the drum head. This was achieved by simply moving the mic off axis in relation to the beater. Still slightly plasticky, implying that there is some as yet undisclosed issue with the internal acoustics of that particular kick drum, but far less problematic than before, and with acceptable depth and precision. An RE20 was used in this application.

 
 

Overheads

Overheads were assessed in two ways; by exchanging microphones and by raising their position above the kit. The fundamental technique however always remained the same: both microphones positioned in a straight line either side of the kit, face-down directly above their respective cymbal clusters. Incidentally, it was a point of contention between Chris and I regarding which overhead microphone is considered “left” and which is “right”, with my firm belief that, as a drummer myself, it is appropriate for the stereo spectrum in the mix to be situated in a way that makes sense to the drummer – a right-handed drummer has his high-hat on the left-hand side. Anything else is disorientating and conducive to travel sickness. I fully accept, however, that not everyone shares this view, and some (most, probably) consider it appropriate to balance the mix from the audience’s perspective, rather than the musician’s. Personally my view is that the music was created entirely from the musicians’ perspective, from the composition to the lyrics to the performance, and therefore the recording and mix should reflect this and not be tailored to the perspective of an abstract person whose role is no more than an observer. I understand that a gig scenario has different connotations because a large audience is actually present and looking at the band, and therefore probably expects that their visual reference correlates with what they are hearing, but a recording is a musician’s opportunity to speak, unobserved, directly to an audience from their perspective. That’s why, to me, the high-hat side (for a right-handed drummer) is always OH L, and the floor tom side is always OH R. But whatever side of the fence you fall on, just make sure that you and any assistant engineers are all on the same page. It could lead to confusion.

In positioning the overheads, it was found that, for a hard hitting drummer such as myself at least, close miking the cymbals was inappropriate in that the attack part of the cymbal felt ear-splittingly harsh, whilst the sustain was largely unrecognised by the microphone. Not only this, but, as is often the case when overheads are too close to the cymbals, the movement of the cymbal creates an undesirable phasing effect. The remedy to this was to raise the microphones up to around four feet above the cymbals, being sure at all times that both microphones were equidistant from the snare, such that the risk of snare phasing could be minimised (an XLR cable makes a handy measuring device for this task). In this position, although allowing more room ambience into the microphone (which, in a room that sounds as functional as this, poses no problem), a good balance of the kit could be achieved with great stereo imaging. There was talk of elaborating on the positioning by trying a coincident pair or some such oft-referred to but curiously never observed technique, but given that the stereo imaging was doing everything we needed it to do here, it seemed inappropriate to change it.

The mics tested were as follows:

Microphone  Rank Comments
Coles 4038s 1 Deceivingly dark sounding microphones, such that on first glance they appear entirely inappropriate until you realise that they are perfectly balancing the kit and smoothing out all the aggressive high end usually present in overhead microphones. Very dry and functional sound without excellent body.
Neumann U87s 2 A bright, clattering sound, rich in upper mid detail but inappropriate for this application without significant EQ treatment.
Neumann KM187s 3 Very bright with excellent high end detail and transient response, but as such renders clattering cymbals ear splitting.

The individual recordings of this test can be found here.

 
 

M/S Room Mic

An essential component of the “Albini” drum technique is the placement of a cardioid/figure-8 arrangement in front of the kit, with the side mic aligned to face the walls perpendicular to the direction of the kit. The principle of M/S (mid/side) recording is that, whilst a directional microphone captures the sound source, a figure-8 mic captures a stereo image by means of polarity-inverting a duplication of its signal, the two of which are then hard panned left and right. And so it was in this test that, after experimenting with the positioning of the mic in front of the kit, moving it increasingly further back until the most desirable spot was found (around four feet from the kit and 2½ feet from the floor), the resulting trickery harboured subtle ambience which lent itself nicely to the width of the kit. It was however important the right microphones are used, as the initial choice of Audio Technica AT4050 – although a great microphone for many instances – actually sounded too bright and revealing here. Cymbal clatter is a large problem in ambient drum miking, and so use of ribbon mics – in this case the Royer 121 – provided just the right amount of high end roll off that served the sound well, although ultimately, at mix stage, the high end had to be further attenuated to minimise the clanging clutter as much as possible.

 
 

Ambient Mics

With the essential sound of the kit now nicely built up, and the drums thumping through the speakers in a way that has not been observed by any of us in any studio this side of Chicago, ambient miking became merely a matter of taste, the essential function of which was to add a little extra something into an already more than serviceable sound. In this regard, we spent little time experimenting with different microphones and placements, but instead went with a tried and trusted technique of using two fairly transparent sounding omni mics (in this case some custom built Panasonic WM-61s – two surprisingly high quality electret capsule mics that I built some time ago) placed ¾ of the way up the wall at the back of the room, thus utilising the principle of the boundary effect. Boundary microphones exhibit more accurate definition due to their being uninhibited by the comb filtering effects caused by wave cancellation from nearby boundaries – placing the mics on the boundary itself reduces such an undesirable effect.

Following this, a rusty, vintage tube microphone was placed in the corridor outside the live room in order to capture what I have come to regard as “a bit of fun” – special effect ambience that you can take or leave, depending on taste. Just compress the crap out of it and – presto – instant drum fun.

And so essentially, that was it. All this experimenting resulted in a drum sound that, when played back, just about knocked your head through the rear wall, which is precisely the effect we were striving for. If you would like to hear for yourself, you can find the resulting files here.

For the time being, anyway, I’m off to give my fingers a rest from about three hours’ constant tip-tapping. In another post I will elaborate on the mixing process following these techniques, as one or two tricks should be employed in order to suitably manage such a large number of independent signals. However, for the time being, this appears to be the secret of the Albini method.