Recording techniques:Piano

The Sound Board
While a piano may look like a harp on the inside, it is actually much more like a guitar. While the hammer hitting the strings makes the tone, the sound board is what amplifies and resonates the tone. On a grand piano the sound comes from the giant sound board on the bottom. On an Upright piano, the sound resonates in a sound board on its back.

The Moving Parts
People often forget that music is not the only sound that comes out of a piano. Not only the strings, but all the moving parts, including the pedals, hammers and keys also make noise. In particular, the pedals can make a loud thumping noise that is resonated by the sound board. Depending on how good the pianist is and the quality of the piano, this noise may be unnoticeable or annoyingly loud, and how you place the microphone can drastically change the loudness of these sounds to good effect or bad.

Ways to Mic a Piano
Depending on the setting, the type of piano, and the sound you want, there are different ways to mic a piano.

Mic the Room
If you are recording just a piano, placing your microphones in the room at a distance from the piano may be your best option. Micing the room reduces the noise of the moving parts and gives the piano a "natural" sound. However you will lose attack. If the piano lacks attack, move the mic's in towards the piano or combine close micing and room micing to effect.

However, if you are recording a singer who plays the piano or a piano in a band, you will lose the ability to change the level of the piano in a multi-track mix.

To Mic the piano's room, first take into account the acoustics of the room. In general a smaller, boxy room would be less ideal, and a larger more diffuse room that has non parallel walls or angles that diffuse the sound will be more pleasurable. If you decide you want to try a room setup then spend some time moving the mic around the room to find the "sweet spot." Preferably, if the pianist is hard on the pedals, keeping the mic at a distance from the piano is a good idea. To learn about how the room could be affecting the sound of your recording check out Studio Acoustics.

A good place to start for a mono room mic would be 4-8 ft out from the piano, and 4-8 ft in the air, keeping in mind that if it is a grand piano then changing the top deflector board will not only change the apparent loudness but also the amount of reflections both from the board and the other surfaces of the room.

Using a stereo mic pair is also a good idea. To garner the most "accurate" portrayal of the piano's sound, two high quality omni-directional microphones placed in an AB pattern is a good first try. This will help to give the listener a sense of the space the piano is playing in. The AB Stereo Microphone Technique, XY Stereo Microphone Technique and the Mid-Side Microphone Technique could all work depending on what you want.

Mic'ing the Piano Directly
Placing multiple Microphones close to the piano can help you gain a better control of the sound during the mixing process, and also gives you much better attack. An AB pattern about 6" off the strings of the grand piano with one mic on the lower strings and one higher can get a good tone with a nice amount of attack. However, you are more likely to mic up the noise from the moving parts of the piano.

Below the Piano
Placing microphones below the piano allows you to mic the soundboard. Try moving the mic around sound board to find the sound you are looking for.

A Stereo pair underneath the piano should work well, but you can also try placing three mics at the extremes of the sound board in order to have control of the volumes of the lows, mids and highs.

In the Piano
By in the Piano, I mean under the hood. Don't try sticking mics into the sound holes. Place an XY pair at the edge of the lid, aimed in towards the center of the hammers.

By the Pianist
If you place the mics by the pianist, you will get more of what the pianist hears.

Mix and Match
If you have enough microphones and enough channels, you could mic the piano in several different ways and then LISTEN, as no manner of tutorial is ever going to replace a set of good ears and taking the time to try move the microphones around and grab a good sound. Another tip is to go into the room with the piano and listen to how it sounds in different parts of the room, and the move your mikes and then when you listen you can try and capture what you just heard.

Reference
Wikirecording guide to pianos