Acoustic Piano Miking Workshop

Though the acoustic piano isn't exactly Paul White's forte, he (fortunately) knows rather more about miking it up than about playing it...

With so many excellent and inexpensive MIDI piano modules currently on the market, you might wonder why anyone bothers to go to the trouble of recording the real thing — or at least, you might if you haven't already listened to the difference between a good piano and its sample‑based emulation. Now, I didn't get where I am today without knowing the difference between a good piano and its sample‑based emulation; the truth of the matter is that a piano is a living, breathing instrument full of resonances and vibrations that are far too complex to emulate with absolute accuracy. For example, whenever you play a note on a real piano, the other strings also vibrate in sympathy, but in different ways depending on which note you've played and how hard. If you play two notes at a time, the pattern of sympathetic resonances gets more complex, but because of the way in which most electronic pianos are sampled, the best you can hope for is that each note will be accompanied by the sympathetic resonances that occur when that note is played in isolation. And unless each separate note is sampled (as opposed to one note being transposed to cover several keys), the resonances will also be transposed depending on the note you play.

Then there's the way in which the timbre changes with dynamics to consider. Velocity crossfading between a few discrete samples or using a velocity‑controlled filter is never going to capture the subtle nuances of a real piano played by a virtuoso performer, and while a MIDI piano might be fine as part of a mix, few piano players feel entirely comfortable using them for solo performances or prominent parts. In such cases, there's no alternative but to get out the mics and record the real thing.

The Piano Sound

When it comes to recording, the acoustic piano isn't without its problems; for a start, the sound doesn't just emanate from one convenient point but from the strings, the soundboard and the casework of the instrument, and it's only when all these vibrating parts make their contribution that a true sound can be captured. To further frustrate the recording engineer, there are various mechanical noises, such as the pedals and dampers, that must be minimised. A change in playing style is sometimes all that's needed, but it's not uncommon to have to wrap the pedals in cloth to stop them thumping. And, of course, you have acoustic spill and room acoustics to worry about.

The Grand Gesture

Most important piano recordings are made using a grand piano unless the musical style specifically needs the sound of an upright, and it's generally thought that the larger the piano, the better the sound, especially at the bass end.

Before getting into mic positions, it's necessary to think about the sound of the instrument and the type of mics that will be needed to do it justice. The piano spans the entire musical spectrum, from deep bass to almost ultrasonic harmonics, so a microphone with a wide frequency response is a must. A good capacitor or back‑electret microphone is the preferred choice, though you can exercise a degree of artistic choice in deciding to go for a ruthlessly honest small capsule model, or a more flattering but less accurate large‑diaphragm mic. Aside from their excellent frequency response, capacitor mics are very sensitive, which means they'll be able to capture the dynamic range of the instrument without introducing unwanted noise, even when you're recording from several feet away. For demo work, good dynamic mics will produce acceptable results, but capacitor models are really the only choice for release‑quality recordings.

Pianos are most often recorded in stereo and any of the standard stereo mic techniques may be applied. You can use spaced omnis, coincident cardioids, MS pairs or PZM mics, though if you're worried about mono compatibility, you may feel safer sticking to a coincident mic setup rather than a spaced arrangement, as spaced mics, by their very geometry, introduce phase effects which may cause the sound to change for the worse when you hit the console's mono button. On the other hand, spaced microphones do allow more control in balancing the upper and lower registers of the instrument if you opt for a close‑miking approach.

Some engineers habitually use three or more mics, but this runs the risk of more serious phase problems, so unless you've got plenty of time to experiment, it may be safer to stick to a stereo pair. The only exception to this rule is when using spaced omnis at a distance from the piano, as this often leads to a lack of definition in the centre of the soundstage — an additional centre mic can help to hold the sound together.

Mic Positions

Before deciding on a mic position, decide on the sound you want. Pop recordings may require a bright, up‑front sound, where accuracy is less important than getting the right type of sound, while for classical and jazz work, you will probably want to capture the instrument as accurately as possible, including a little ambience from the environment.

Assuming that the room is sympathetic to the piano and that spill from nearby instruments isn't a problem, a simple stereo pair positioned between six and ten feet from the right hand (opening) side of the piano may be all that is needed. If the sound is becoming clouded by room ambience, you can move in closer, whereas if the room is making a positive contribution to the sound, you can afford to move the mics further out. Choosing cardioid mics means that you can work further from the piano than with omnis for the same amount of spill or room ambience, so if the room really isn't helping the sound, using cardioids or even hypercardioids might help.

Keep the mics at a height such that they're aimed about halfway up the inside of the open lid. If the room acoustics dictate that the mics have to be brought in very close, it may be advantageous to add a little artificial reverb afterwards, though this should be used sparingly because the sympathetic resonances of the piano's own strings and sound board provide a type of reverb. Figure 1 shows a suggested position for both coincident and spaced mics.

For pop work, close miking is often employed to create a more cutting, 'in‑your‑face' sound and one popular technique is to position the microphones inside the open piano lid between six and ten inches from the strings, close to the position where the hammers strike the strings. Though cardioids may be used, omnis might be a better choice as they have a more accurate off‑axis response which tends to produce a more even tone across the strings. One covers the higher octaves and the other the bass end, and though this doesn't produce an accurate stereo recording, it does sound good in stereo. Having said that, it may not be wise to pan the two mics to the extremes, as you could end up with a piano that sounds about 20 feet wide! Trust your ears on this one and use just enough panning to create a convincing end result.

Close miking has the additional benefit of reducing spill from other instruments, and if even greater separation is necessary, blankets may be draped over the piano lid so as to cover the opening.

With any method involving spaced mics, whether close or distant, it's as well to do a mono compatibility check by running through scales using the whole keyboard. Any unduly loud or quiet notes, or groups of notes, that may be attributable to phase addition or cancellation should be quite evident, and if the mono compatibility has suffered too much, try changing the spacing between the mics slightly and ensure that there is at least three times (and ideally five times) the distance between the two mics as there is between the mics and the strings. Figure 2 shows a typical close‑miking arrangement.

I've suggested a few mic positions based on experience and common practice, but don't be afraid to experiment, because nearly all initial mic setups can be improved upon or fine‑tuned simply by trying new positions. For example, if you need a more mellow tone or a fuller sound, think about putting a mic under the piano to capture more of the sound from the soundboard. Similarly, if the room is too live or coloured, improvise screens around the piano using bedding or sleeping bags.

Upright Pianos

Though this description is likely to offend the purists, the upright piano can be thought of as approximating a grand piano turned up on end — when it comes to miking it up. The sound board is now at the back rather than underneath, and because there's no single, large lid covering all the strings, the only way you can close‑mic it is to remove some or all of the front panelling.

The upright piano has a noticeably different tone to the grand, especially in the bass register, where it produces a less rich sound, but you can still get a good miked‑up sound with a little perseverance. A stereo pair, either coincident or spaced, can be positioned on boom stands above the instrument, with its top open. Check for an even tonal balance right across the range of the instrument and move the mics if there are any obvious dead or hot spots. Spaced mics are easier to use as they can be moved independently to balance the high and low end of the instrument, but the down side is, as ever, the potential for audible phase problems.

Standing the piano close to a solid wall can help to beef up the bass end by getting the boundary effect on your side, and if the room suits the piano sound you're after, you can move the mics back to a few feet behind the player. A room with a tiled, wooden or stone floor will help maintain a bright, lively tone, whereas carpet will tend to rob the sound of some of its sparkle. If you're struggling to get a mic position that works, it's always worth remembering that an instrument nearly always sounds OK to the person playing it, so try setting up the mics to 'look' over his or her shoulders.

When close‑miking the upright piano so that the mics are pointing directly at the strings, you can choose to mic either the section beneath the keyboard or the section above it, the main concern being to get an even level across the keyboard and to check for mono compatibility.

Because upright pianos are often set up in imperfect rooms, and because a great many of them are indifferent instruments, a little equalisation may be useful in shaping the sound to your needs. However, keep EQ to a minimum; use gentle slopes or cuts rather than harsh boosts, and to add sparkle, use a little boost at around 6kHz, or apply an exciter (sparingly). An indifferent upright played in a carpeted room may benefit from both high‑end EQ and a little artificial ambience or reverb, plate settings being the most flattering.

I hope that this article has shown that there's no real black art to recording the piano — you just need to apply a little logic and be prepared to experiment. If you're on a tight budget, a couple of cheap PZMs from your local Tandy shop will work far better than they could reasonably be expected to, given their price, and with the preponderance of cheaper capacitor mics, even doing the job seriously isn't prohibitively expensive. Don't be afraid to give it a try — providing your mics are half‑decent and the piano is in tune, you're almost certain to end up with a usable recording.