ORTF microphone technique

For several years I’ve been making recordings of church choirs, usually accompanied by an organ. I’ve been using a pair of Behringer C-2 small diaphragm cardioid condenser microphones, and until now I’ve been reasonably pleased with my technique – and then I tried the ORTF technique.

X-Y technique

In the past, I’ve always used the X-Y technique, where two cardioid microphones are arranged so their tips are in the same position, and angled 90° apart.

I’ve been using a pair of small diaphragm cardioid condenser microphones to capture the choir in stereo. My small diaphragm microphones have fairly poor low frequency response so I’ve been adding a single large diaphragm condenser microphone to pick up the low frequencies, and adding it to the mix with a low-pass filter of about 100 Hz – effectively playing the role of a subwoofer. I record multitrack, so it’s possible to decide on the levels later on, and omit the extra mic if necessary.

ORTF technique

So this week, for no particular reason I remembered the ORTF stereo technique and decided to try that at Candlemas choral evensong. I really hoped it would work out because the choir were singing one of my favourite pieces – When to the temple Mary went by Johannes Eccard.

In the ORTF technique, two cardioid microphones are angled 110° apart, with their tips 17cm away from each other. This mimics human ears.

On paper, ORTF gives a more realistic stereo image, at the expense of being not quite phase-safe if flattened to mono. That’s a gamble I’m prepared to take – I can’t think of any real reason why this choral recording would be played back in mono. I also added my large diaphragm to pick up the rumble of the organ.

Theory is all well and good, but how did the ORTF technique stand up in the real world? Well, I thought it sounded great. The choir was bright and clear and yet smooth and rich – the dainty sounds of the vowels showed through clearly without being overly sibilant. Stereo placement is excellent and the image is a pleasure to listen to.

As expected, there was a lot less room ambience and reverb picked up – presumably because the microphones are facing more towards the side walls. I think I could fix this by moving the pair of microphones around the building. However, it had a nice side effect that it also picked up less of the congregation’s fidgeting, which is always a bonus when recording a church service.

Surprisingly, the low frequency pickup of the small diaphragm condensers seems vastly improved in the ORTF arrangement, so I didn’t even bother listening to the track recorded on the large diaphragm.

So I think that settles it. For this kind of work in the future I will be using the ORTF stereo microphone technique, provided I can experiment with the microphone positioning to capture the best room ambience 🙂