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Occasional posts on subjects including field recording, London history and literature, other websites worth looking at, articles in the press, and news of sound-related events.

15 February 2010

Head-worn mics for under £300

IT DOESN’T HAVE to cost a lot to start making field recordings. A digital recorder and set of half-decent external mics can work out cheaper than most entry-level digital SLR camera kits. Banned from the eBay forums? Need a new hobby? Sorted!

Many of the recordings in the London Sound Survey are made using head-worn mics. That is, two small omnidirectional mics are worn on each side of the head, with their leads converging onto a single jack-plug which goes into the digital recorder. Each mic by itself can only record in mono. Used together, though, they can produce recordings with a very realistic-sounding stereo image. This is partly because the mics will be the same distance apart as your own two ears, and also because your head acts as a sound-absorbing and sound-colouring baffle between the mics.

You might have come across the term ‘binaural stereo’ or ‘binaural recording’. Strictly speaking, binaurally-positioned mics are put inside the ear canals. Binaural recordings can have extremely lifelike stereo images, but they usually only come into full effect when listened to through headphones. They just don’t sound as good over speakers. Positioning the mics elsewhere on the head, typically just before the ears or at the temples, produces a stereo image that sounds equally good over headphones and speakers. The term ‘head-worn stereo’ is used here to describe this particular recording arrangement.

Fortunately, several firms produce mics for binaural or head-worn recording, and many of the models are pretty cheap. There’s now a handy list of 28 different models on this page . . .

http://www.soundsurvey.org.uk/index.php/survey/budget_mics/

. . . gleaned from different websites, and because there are different ways of expressing some of the specifications, they’ve been standardised to make comparisons easier.

Self-noise is shown in dBV, eg 23dBV, and the higher that value is, the noisier or more hissy the mic. Relatively high values like 34 or 36dBV aren’t going to be a problem if you’re recording at gigs or other busy places, but you might not be so happy with the results if you’re trying to capture the subtle ambience of Victoria Coach Station at two in the morning.

Sensitivity (or, more correctly, the ‘transfer function’) is expressed in values of mV/Pa. The higher the value, the more sensitive the mic is. Again, whether a high or a low sensitivity is good or not depends on what you’re going to do with the mics. But 10 mV/Pa seems to be an acceptable average value, and it’s probably best to go up from there rather than down.

Lastly, maximum sound pressure levels are given, and these are the levels of loudness at which the mics begin to produce unpleasantly-distorted sound. The value of 105dB is the most common in the list, and that’s alright for many everyday recording situations, but it won’t be enough for loud gigs or if you’re in the middle of a crowd at a football match. For those kind of events you’ll probably want to look at something like 120–130dB.

There are two models in the list which fall in that range, and a few others that will approach it provided they get a slightly higher voltage from one of the custom-made battery boxes which many of the manufacturers will be eager to sell you. Otherwise, all of those mics run on the plug-in power, or PIP, which just about any pocket digital recorder can supply through its mic socket.

The list page is quite basic right now, but a few little features should be added to it shortly. If you’ve got any experience of using any of those models, then please feel free to make a comment on that page and share your knowledge.

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