How is a piano recorded?

In a nutshell-usually poorly. They are tough to get right.
We all wish that records/cd's sounded as you describe-as a whole unit- but most don't.

A few years back I co-funded a recording by a small jazz band featuring a friend - Richard Todd - who is a noted French Horn player. In watching the recording sessions, it was apparent that getting the piano right was going to be the biggest problem. When the set-up was finally complete, the band played its first tune and we had a great sounding take. However, when we listened to playback of the performance, the piano BENCH was squeaking throughout. Suffice it to say that it's very, very tough to get this right.

Firstly ou should understand how a piano produces it's sound. All the strings are connected, by tension, to the sound-board. The sound-board is like a big diaphram witch amplifies the string's vibrations. The sound-board projects the sound (if it's a grand) up against the lid and down towards the floor. You don't 'mic' the strings but rather the sound-board. I found that by placing the mic or mics 2 meters away from the 'sound-board' makes for the best recording. I also would never place a mic inside the piano cabinet or near the strings. This is wrong as you get a peak in the frequency were the mic sits - say for instance its near a middle A flat.

There are several ways to mic a piano and it all depends on what you want the results to sound like. I do a lot of recording for a live radio broadcast and for various artists and will vary my recording tech. depending on the results I desire.

The problem with recording solo piano in a realistic manner is that it can lack impact and not hold the listener's interst, especially if there are vocals. Getting the soundstage right with vocals and piano is very difficult, so in order to create a soundstage that holds the listener's attention a lot of engineers create a 10 foot wide sound stage with the lower register extending stage left and the upper, stage right.

This, of course, makes for interesting runs but can be a bit annoying for those that want an audience perspective rather than an artist.

So in short, there is no right or wrong way but rather multiple ways that can shape the results you want.

My favorite way is to use one pair of close mics ORTF mics, starting around middle C, slightly turned at around 40 degree angled back on the lower register and forward on the higher. I then place two split omni's, spaced around 5-6 feet in front of the paino and then post mix to my liking.

I am a simpleton in this crowd - generally just interested in hearing good stuff without a lot of concern about the technicals. But I recommend the cd Chick Corea and Herbie Hancock Duets. I have found that the recording produces the whole, integrated sound you describe, but there is a l-r separation for the pianos themselves, a very good recreation of the back and forth of two masters.