Recording Piano: How Pianos Generate Sound

Andrew —  — 1 Comment

Piano2

Pianos are arguably the hardest acoustic instrument to record well. They are capable of producing a frequency range wider than humans can hear, and the way they radiate sound is not at all linear so moving a microphone a foot or two, or even a couple of inches can completely change the tone it picks up.

In this article we will look at how a grand piano creates sound, then we can explore some different mic techniques to make the best use of that knowledge. After that, we will apply everything to recording upright pianos as they are much more common than grands.

The Keyboard and Hammers

The keyboard is where it all starts on a piano. The keys are connected to a set of felt hammers via an intricate collection of  levers, flanges and dampers, collectively know as the ‘action’ (pictured). When a key is pressed, the action raises the hammer which in turn hits the strings.

How do they sound?

The keyboard itself makes almost no noise at all, but the action can be surprisingly noisy as the moving parts hit pads and dampers. This isn’t a particularly musical noise (see here for an example) so generally speaking it’s best to keep it out of the recording as much as possible. The sound of the hammer hitting the string is very crisp and immediate, so it can be used to add that tone to the overall piano sound but you will have to be careful to avoid getting a lot of action noise.

The Strings

The sound of  the strings vibrating doesn’t contribute very much to the overall sound of a piano, instead their vibration is passed on to the soundboard which they are mounted on. The lower strings are the longest, so they usually overlap the middle strings to save space. This can make miking up the middle strings difficult as the only place they are exposed is quite near the hammers. The higher strings are usually arranged three to a note to balance against the thick and heavy bass strings, but they still won’t radiate very much sound in comparison so they need to be miked closely.

How do they sound?

The strings themselves sound very metallic and sharp which is not particularly pleasant as the main tone of a recording, but when they are mixed in with other mics they can add a very clean and bright character. Pay close attention to the sound of the higher strings because as you move a microphone towards the tail end of the piano, the top end will quickly become drowned out by the much heavier bass strings. By experimenting with position you should be able to find a decent balance between the top and lower strings. If at this point the middle strings are a little lost in the mix, you can recover them by moving the microphone further into the body of the piano.

The Soundboard

The vibrations from the strings are passed onto the soundboard, and as it has a much larger surface area it’s much more efficient at transferring those vibrations to the air as sound. This is where all the guts of your piano sound is going to come from, whether you mic up the piano as a whole or right up close to the soundboard. Since it is lying flat, the soundboard will radiate sound downwards just as much as it will up, which is useful to know if you need to mic unobtrusively as you can mic it from below.

How does it sound?

Up close the soundboard sounds very warm and doesn’t have much top end, especially if you are miking from underneath the piano. Blended in with the rest of the piano it will sound full and rich, whether this is with a combination of several close mics or a pair of ambient mics . The tone doesn’t vary very much across the soundboard, apart from being a bit more bass heavy at the tail end so you are unlikely to gain much from stereo mics.

The Lid

I know it may seem odd, but the lid is extremely important to the overall sound of a piano. The lid reflects the sound coming from the strings and the soundboard out towards the front of the piano. Most of the time the lid is fully up to direct as much of the sound towards an audience as possible, but you can drop it down to half-stick if you are worried about spill. Lowering the lid will deaden the sound and unless you are close miking it will also sound a lot less bright. With the lid completely closed the piano will sound dull and lifeless.

You may have seen grand pianos with the lid removed, and this can be really useful if you are going for a complex close miking technique as it gives you more space and eliminates reflections from the lid which can cause phase issues. If you are recording a grand piano and are not using close mics alone, leave the lid on or you will lose all the brilliance from the top end.

(image via Autoscaph)

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