The Choir Recording

By George Petersen

Once upon a time, making a decent recording of a choral ensemble was difficult and required expensive audio tools and complicated recording devices. These days, the process has become a lot easier. The tools – including microphones and recording systems – are now more affordable. However, aspects like acoustics and physics haven’t changed during that same time, so some attention to those details is still a must: you can’t fool Mother Nature.

Microphone Base

The beginning to any great recording starts with good microphones. Just as a great camera needs a great lens, quality microphones are a must. This doesn’t mean that only a $5,000 microphone will give good results – far from it. There is no shortage of serviceable (and even good) microphones in the $100 to $300 price range, and of course, a good choral recording can be done with a simple stereo pair. But before we get too much further, let’s examine some basics about microphones.

One thing common to all professional microphones is the use of three-pin “XLR” connectors and cabling, as shown in Fig. 1. Low-grade microphones with guitar-style 1/4-inch or mini-jack connectors should be avoided, because these designs are limited to a maximum cable length of about 15 feet before they are subject to picking up hum and noise. Pro mics with XLR connectors use what is called a balanced line (hence the three conductors), which are highly immune to hum and noise pickup.

There are many variations of microphones, but let’s consider the two most common types. Dynamic mics operate when sound waves strike a diaphragm attached to a coil of wire. This coil moving within the magnetic structure of the mic creates an output voltage. Interestingly, the process is exactly the reverse of the way a speaker operates.

Condenser microphones take a different approach. Sound waves striking the diaphragm cause a very small voltage change. Condenser mics must have a power source, which can be a battery inside the mic body or “phantom” power coming from either the mixing console or an external power supply. Extremely rugged, dynamic mics are often used in most sound reinforcement applications and will do just fine, though condenser microphones provide better reproduction of higher frequencies.

Whether dynamic or condenser, all mics exhibit some sort of directional behavior. As their name implies, omnidirectional mics pick up sounds equally well from any direction. More useful in choral recording, cardioid microphones (available in a number of variants), are most sensitive to sounds in front of the mic and actually reject sounds entering from the rear of the mic. Some mics can toggle between these directional modes.

Distance is the enemy

Consider a simple lesson in acoustics. In any venue, once a sound is emitted – whether from a speaker system or a soloist doing an aria at The Met – only part of what you hear is actually the direct sound of that soprano’s voice. Most of what you hear is the myriad reflections of sound bouncing off every surface in the room.

This can give a lush, reverberant quality to the voice, but it’s often buried in a mush of late arriving sounds created by differing pathways of the reflected sounds. The result is a loss of intelligibility – where vocal detail, diction, and even melodic and harmonic changes suffer. It’s great for that first-chair violin solo, but not so good if you’re trying to actually hear and follow the lyrics. The greater the distance from the source, the lower the intelligibility factor.

However, the lesson here is that no matter how wonderful the acoustics of the space, you want the microphones to be fairly close to the voices for choral recording. Depending on the size of the group, somewhere about three to four feet from the ensemble often works best for a vocal group.

Choir-view of a typical X-Y stereo mic configuration using two Shure KSM137 condenser microphones on a single stand using a stereo A27m swiveling mic mount to keep the two mic capsules in close proximity.

Stereo Recording

Oddly enough, with microphone placement, simpler is frequently the better choice. While you could mic a 120-voice ensemble with 120 microphones, you might get better results with two or four mics. And two microphones arranged as a stereo pair can provide surprisingly optimal reproduction.

One popular stereo pair arrangement is the “X-Y” configuration, where the capsules of two microphones are spaced closely together, with the left mic pointed to the right and vice-versa, as shown in Fig. 2.

Another stereo technique uses a “spaced pair,” with the two microphones placed parallel to each other and at least several feet apart.

The X-Y method offers less chance of stereo image “smearing,” because sounds arrive at both capsules nearly simultaneously. The spaced pair technique provides a more dramatic stereo effect, but extreme left and right sounds may be emphasized more than sounds coming from the center. Both of these stereo techniques are frequently used on stage and in the studio, and both can provide excellent results. With very large ensembles, the spaced “pair” technique may require three or four microphones placed across the front of the choir. These can be captured as separate channels and assigned left/right panning during the mixing phase.

With very large (or deep) groups, I’ve used a combination of mics with one stereo-spaced pair at the front of the group and a second spaced pair on tall boom stands to capture the voices from a second or third rear riser. I used this on a concert presented by the Oakland Youth Chorus (see Fig. 3), with excellent results.

Sounds arriving at different times to spaced microphones can not only decrease intelligibility, but also result in what’s known as “comb filtering.” Despite the silly sounding name, this is a nasty effect that can actually create destructive acoustical cancellation, where certain frequencies are attenuated.

Applied to a spaced pair of microphones in front of a vocal group, the 3:1 rule states that the distance between the two mics should be at least three times the distance from the source.

When using spaced pair or multiple microphones, the distance between each microphone should be at least three times greater than the distance between your microphone and the source. This will minimize acoustical cancellation effects. In practice, this 3-to-1 rule applies equally to stand-mounted or hanging microphones. Fig. 4 shows a correct application of the 3-to-1 rule with a chorus, where the distance between the two mics is approximately three times the distance of the mics to the source.

The Recorder

Again, once upon a time, recorders were expensive, bulky, and complicated. Today, they can exist even as simple, compact handheld units. Alternatively, many companies offer hardware interfaces (often bundled with basic recording/editing software packages) that allow capturing stereo or multiple microphones directly to a computer, through USB or FireWire connections. And some modern P.A. mixing boards (such as the PreSonus StudioLive) have USB or FireWire ports that can output stereo or multiple tracks directly to a computer for recording.

One popular, affordable portable recorder is the Zoom H4n (street price around $270). It can record four tracks simultaneously — two from its built-in stereo mics and two from XLR inputs.

These days, there is no shortage of small, affordable handheld recorders of decent quality. These are available from a variety of suppliers, such as Korg, Marantz, Roland, Sony, Tascam, and Zoom. Battery or AC-operated and equipped with built-in mics and XLR inputs for external mics, models are available with two, four, or six recording channels and store to removable media such as SD or Compact Flash cards. All are fairly simple in operation and are easy to use and tracks can easily be transferred to a computer for editing, mixing or processing.

One popular and affordable portable recorder is the Zoom H4n, which has street price around $270. It can record four tracks simultaneously – two from its built-in stereo mics and two from XLR inputs).

One of my favorite tricks for choir recording is to use a portable four-track recorder, set farther back in the hall, using the built-in mics to capture audience sounds, applause, and so on. Nearly all of these recorders also have a threaded mount for a standard camera tripod, so I don’t have to hold the recorder for the entire show. I then feed the two XLR inputs from a stereo pair set up on stage, closer to the singers. This gives me two perspectives, which I can mix later for just the right blend of ambience, choral articulation, and audience.

It Can Be Done!

Hopefully I’ve given you some basic knowledge and perhaps even some inspiration to try doing your own recordings. And if you do, don’t wait until the day of the big recital to get started. Begin by familiarizing yourself with the gear you have well before that big day. Experiment with different microphone placements and combinations during rehearsals and find out what works for you and your ensemble. Also, enlisting the help from a good volunteer crew is essential. A little extra help can go a long way.