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Tuesday, May 22, 2018

Q. What mics should I use on a snare drum?

By Hugh Robjohns

I am looking at buying a matched pair of SE Electronics SE1 mics for drum miking. I am prepared to pay more for the right mics, but would the SE1s be suitable for 'over and under' miking of the snare? If not, could you offer any alternatives for this kind of configuration?

SOS Forum Post
If you're going to 'over-and-under' mike a snare, remember to switch one of the mics out of phase. 
If you're going to 'over-and-under' mike a snare, remember to switch one of the mics out of phase. 

Technical Editor Hugh Robjohns replies: The SE1s are great as overheads, but I'd be wary of using them for close-miking a snare. In the case of jazz drumming you might get away with it, but for a heavy-handed rock drummer with a loud snare, you stand a very good chance of overloading the mic's internal head amp.

Looking at the published specs, the SE1 is rated with a max sound pressure level (SPL) of 130dB for 0.5% total harmonic distortion (THD). If you really want to use small-diaphragm condensers, I'd suggest something like the Rode NT5, which is rated at 143dB SPL (albeit at 1% distortion), and so should be able to cope with a close snare a lot better.

It all depends on the kind of snare drum sound you are after, but condenser mics on snares can sound rather lightweight and thin. They deliver the transient 'thwack' of the hit very well, but often lack body. On the other hand, a good dynamic mic, like the venerable Shure SM57, inherently 'soft-limits' the transients and gives a much thicker, more full-bodied snare sound.

The over-and-under technique can be useful, as long as you remember to phase-reverse one of the mics. This is because when the stick hits the batter head, the head moves away from the top mic, producing lower air pressure (an initial rarefaction), while the snare head moves towards the bottom mic, producing a rise in air pressure (an initial compression). If you mix these two together without inverting the polarity of one of them, the two opposite pressure waves will tend to cancel each other out, and result in a very thin sound. Flip the phase of one mic (usually the bottom one, but it depends on the phasing of any other mics around the kit), and you should get a really big-sounding snare.

It's a good trick to experiment with, but not essential, and in general if you position the right mic in the right place above a good, well-tuned snare drum with a decent batter head and a competent drummer, you should still get excellent results.
Published October 2004

Saturday, May 19, 2018

Q. Can I use acoustic screens to prevent drum spill?

By Hugh Robjohns
Using mic pickup patterns to reduce spill.Using mic pickup patterns to reduce spill.

I'm wanting to record a band all at the same time and in the same room, and my main problem is that the drummer is much too loud. I'll be recording them in a rehearsal room and I'm worried about the other performers' mics picking up excessive spill from the kit. Would it be possible or advisable to try and isolate the kit using some screens? I've seen live performances on TV where the drummer is boxed off with clear perspex screens. Would there be a suitable DIY alternative?

SOS Forum Post

Technical Editor Hugh Robjohns replies: It's virtually impossible to use free-standing screens to generate useful or effective sound isolation, but they can be helpful in reducing spill. They are most effective at high-mid and high frequencies — the laws of physics, the wavelengths of the sounds involved and the physical size of the individual screens determine which frequencies a screen will stop (or, at least, reduce) and which it won't.

Don't expect screens to be able to help much in controlling low-frequency spill — the long wavelengths of low-frequency sounds mean that the spill will get everywhere no matter what! But you can screen off some of the mid- and high-frequency sounds, such as cymbal splashes and snare noise.

In my experience, rather than trying to box in the drum kit in an effort to stop its sound from escaping, screens work much more effectively if you place them around the microphones that are picking up the most spill, to try to keep the unwanted sound from reaching them. In terms of reducing the amount of drum spill recorded, stopping it leaving and preventing it from arriving come to pretty much the same thing, but the latter is far easier and more effective!

You can also reduce the amount of spill by paying careful attention to where you position the musicians relative to each other in the studio, the polar response patterns of their microphones, and where you point those mics. Cardioid and hypercardioid pickup patterns (see diagram above), which reject sound coming from the rear and, to a lesser extent, from the sides, are the order of the day. Don't forget that, in addition to the direct sound from the kit, the other mics may also be picking up reflected sound from the surrounding walls. In such cases, an additional screen behind or to the sides of the performer and microphone can help to cut out those unwanted reflections.

Boxing in the drum kit with hard reflective surfaces (like perspex panels) often causes more problems than it solves. It is a necessary evil on sound stages sometimes, but as I say, I find you can get better results if you concentrate on trying to stop unwanted sound getting into specific mics from specific directions, rather than trying to stop the unwanted sound from leaving the source. That's more of a job for King Canute!

At the end of the day, you will probably have to live with a degree of spill, but this is not the end of the world, especially if you're aiming for a 'live' sound. In fact, in most cases a modest amount of spill only becomes a major problem if you want to overdub something like a completely different guitar solo, when you can still hear the original in the spill on other tracks! Barring any problems with phase cancellation (where spill from a more distant mic interferes with the close-miked signal — switching in phase reverse on the mixer channels for the distant mics should help solve the problem), spill can even help to knit the mix together in a subtle way.

As you are recording in a rehearsal room, in conditions which, I assume, will not be ideal, you will have to compromise — if you can get a dry enough drum sound, and can isolate each instrument enough to have control over the balance of the mix, consider your job done.

Published November 2004

Thursday, May 17, 2018

Q. What is the whining noise coming from my soundcard?

By Martin Walker
Edirol DA2496 word clock.
I noticed a quiet high-pitched whine coming from my Tannoy Reveal Active monitors, which are plugged into my Spirit Folio F14 mixer. Eventually I found that the whine stops when I press the button on my Edirol DA2496 soundcard to select an external word clock.

I get the whine even if the Edirol is not plugged into the mixer, but not if the monitors are not plugged into the mixer. I currently have unbalanced cables from the mixer to my monitors.
I have to use the internal word clock. When any music is playing, it easily drowns out the whine, but I'd rather get to the source of the problem and sort it out.

SOS Forum Post

PC music specialist Martin Walker replies: If you're getting interference even when your soundcard isn't plugged into the mixer, but it stops when you disconnect the mixer from your speakers, it doesn't sound like a problem with the soundcard itself, although you may well be hearing sounds that originally come from the soundcard, probably from its word clock.

As you can hear the interference even when the connection between the soundcard and mixer is broken, I suspect that you're suffering from a ground loop problem which is causing background digital noises to be heard — contrary to popular opinion, ground loops don't only cause background hum. Once there are multiple earth paths, noises from mouse movements, hard drive accesses, and graphic redraws can become audible in the background. Breaking the loop normally results in these all disappearing.

If you have the option of fitting balanced cables anywhere in the chain (mixer to monitors, and soundcard to mixer) this should cure the problem, so try this first.

It could also help if you plug everything into one mains socket via a distribution board, since this will generally make any existing ground loop smaller. It's also worth reseating your soundcard in its socket and tightening down its backplate screw. This ensures a good earth connection from soundcard to the PC chassis.
Active monitors can be a source of problems because they are earthed via their mains lead and via the audio input lead. This is why using balanced connections helps.

However, the only sure way to completely cure ground loop problems is to temporarily unplug all your audio cables and start from scratch. First listen to your powered monitors to make sure they don't exhibit any background noises with nothing connected to their audio inputs (sometimes US models with transformers designed for 60Hz will buzz when running on 50Hz). Then connect the stereo outputs from your mixer to the monitors and check again — if you have the option to use balanced I/O, do so.

Finally, connect the inputs of your mixer one by one to your various synths and soundcard devices with them powered up, temporarily turning up the mixer output volume fairly high after each one is plugged in to see when any hums or buzzes appear. As soon as you hear any noises you've found the offending connection, and can either try making up special pseudo-balanced cables if your mixer has balanced inputs and the source is unbalanced, or try inserting a line-level DI (Direct Injection) box between the device and the mixer input.
Published September 2004