Recording the piano at home – Part 4: Microphone Technology & Stereo Microphone Techniques

I’ll assume that we’ll be recording in stereo. This will allow the recording to give the illusion of space and size to the piano, rather than have the piano reduced to a point-source when the recording is played back through a stereo system. This post is split into two sections. The first covers microphone technology, while the second covers microphone placement techniques for stereo recording.

There are a few things to keep in mind:

  • The microphone’s frequency response must match that of the piano’s. On an 88-key piano the frequencies range from A0 (27.5Hz) to C8 (4136Hz). The Bösendorfer Imperial 290’s lowest note is C0 (16.35Hz), but can be ignored unless you are playing Busoni’s transcriptions of J.S. Bach’s organ works! Although you rarely play the bottom few notes, it is said that sypathetic vibrations of those strings (particularly when the damper pedal is used) adds richness to the sound. Most microphones will meet the frequency range requirement for the piano, but may have sonic signatures objectionable enough that you have to apply more EQ than you otherwise would during mastering. Others designed specifically for vocal use roll-off sharply in the bass to minimize the proximity effect.
  • What the better mics have are higher maximum SPL, wider dynamic range and lower self-noise.
  • You will have to use trial-and-error to find the best mic technique and mic position in terms of tonal balance and amount of room acoustics that you like. Trust your ears – have someone play the piano while you walk around the room. You may even have to get higher and angle the mics downwards so that they point at the strings. It’s largely a matter of personal taste, and depends on the kind of sound you like or are trying to achieve.

Microphone Technology

Stereo Microphone Techniques

There are several different microphone placement techniques for recording in stereo. The most common are shown in the following diagram:

As the arrow on the left of the diagram shows, these different techniques give different kinds of stereo image. Those at the top of the diagram give very distinct and up-front left-right separation of the sound source. Those at the bottom of the diagram yield a stereo image that has less distinct left-right separation but more apparent front-to-back depth. Details about mic techniques can be found at the following resources:

The tape.com article gives the best summary of the differences between several of the most commonly used mic techniques. The Streicher & Everest book is probably the best complete layman’s reference on the why’s and wherefore’s of stereo recording. Highly recommended.

Micing a Piano

See the following for suggested techniques:

You might want to start by trying all of the following mic techniques: AB omni spaced pair, XY pair, DIN Stereo, and Mid-Side. If the room is problematic or good mono playback is important to you then try coincident (or near-coincident) pair techniques like XY and Mid-Side first.

The great thing about Mid-Side is that you can vary the stereo spread and amount of room ambience in post-production. Even if you don’t have a decent figure-8 mic you can achieve the same effect by replacing it with a pair of cardioids, one pointing left the other right, with their capsules as close to the centre mic’s as possible. The Mid-Side technique is often overlooked because it requires you to do some work either during the recording or during post-production to generate the sum-difference matrix. Some audio interfaces (such as the RME Fireface 400) come with on-board mixers that do Mid-Side decoding. Alternatively you can do the Mid-Side decoding in DAW software such as Steinberg Cubase 4, or MOTU Digital Performer. Even Audacity, which is free, can do Mid-Side decoding using a third party plug-in.

A Blumlein pair is also worth trying. The mics are positioned exactly the same as XY, except that a pair of figure-8 mics are used instead of a pair of cardioids. It gives a near-holographic image, but needs a good room. The AB omni spaced pairs technique is very tricky to get right, but can give a very natural sounding stereo image at least as good as that of the Blumlein pair.

Paul Cantrell’s interesting mic technique gets some pretty decent results but largely excludes the room ambience. It also requires you to do a lot more work in post-production.

Microphone Choices

The first thing to do is decide which microphone technique you want to use and note the polar pattern of the microphones required. For example:

  • AB spaced pair – both mics omni-directional, and either matched or at least the same model.
  • XY pair – both mics cardioid, and either matched or at least the same model.
  • Blumlein pair – both mics figure-8, and either matched or at least the same model.
  • Mid-Side – one mic cardioid, one mic figure-8.

If you already have mics with the necessary characteristics, give them a go first before buying anything new. You should be able to get at least a half-decent result. If nothing else you at least have a reference point from which you can work towards a better sound.

If you are buying new and you are likely to experiment with different mic techniques then you might consider multi-pattern mics. If you get modular small diaphragm capsule (SDC) mics then you also have the option of having using interchangeable capsules with different polar patterns. Large diaphragm capsule (LDC) mics don’t have interchangeable capsules, but some have switchable polar patterns.

You then have to decide whether to get SDC mics or LDC mics. The general wisdom is that SDC’s give smoother and more extended off-axis response and are less coloured. Frankly, for home recording purpose, it doesn’t really matter. As for specific brands and models, they range from relatively inexpensive jobs to mortgage-your-home kind of mics. Visit Sweetwater Sound’s ‘Condenser Microphones’ section for an idea of the range of condenser mics in the market. All of the established brands are represented in Singapore by pro-audio dealers.

You will also have to get mic stands, shockmounts for the mics (particularly if the floor is not concrete), a stereo bar or dual-mic mounts, decent cables (with the correct plugs on the ends!), and so on. What you eventually end up with depends on how elaborate you want to go, and how deep your pocket is.

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