Glenn Gould performs J.S. Bach's Partitia No 6 in E minor, BWV 830, Toccata. Bach composed the Partitas (BWV 825–830) as a set of six keyboard pieces, and which were published between 1726 and 1730.
There is a well-known story about Glenn Gould, who when playing Bach pieces composed for the harpsichord, had the piano tuned to sound more like a harpsichord. This was achieved by having the 88 piano keys set in such as way as to have each of the felt-covered hammers strike the steel piano wires at a shorter distance, which was undoubtedly a huge task for a professional piano tuner to undertake.
Yet, it all goes back to the harpsichord, an earlier keyboard instrument. The harpsichord's prominence is intimately linked with the Baroque period, lasting between 1600 and 1750 and which includes Bach's compositions. The piano evolved from the harpischord when manufacturers were looking to invent a keyboard instrument with a better dynamic range. Around 1700, an Italian inventor named Bartolomeo Cristofor, in the court of Prince Ferdinand de Medici of Florence, invented the first piano, shorthand for pianoforte with a range of five octaves.
It would take another century, however, with the advent of the Industrial Revolution and its technological achievements— including developments of new high quality steel called piano wire, and the ability to precisely cast iron frames—before the piano would supplant the harpsichord as a keyboard instrument. Technological advances also increased the range to seven or more octaves common on modern pianos.
Yet, when Gould played Bach he likely wanted to feel Bach's "spirit" on the keyboard. Hence his tuning requirements. Gould's focus on originality and attention to detail is recounted in an article, "Glenn Gould and Piano Tuning" by Jim Ediger, editor for Northern Lights News (1997), referring to his mentor, Ted (Edward) Sambell, a master piano tuner:
In my second year, on a class trip to the Steinway factory on Staten Island, NYC, Ted told me a story about Glenn Gould. Just a few years earlier, he'd been asked by Gould to go down to a studio in New York City to rework and tune the grand piano there in preparation for a recording session. While most pianos have a key-touch depth of 10 millimeters, Glenn wanted his to be only seven mm., which would make it more like a harpsichord keyboard. The lesser depth and key-leverage would decrease the powerful grand piano's dynamics, thus making it better-suited for the more restrained baroque music he would be recording. It also meant that the the key-height and whole piano action had to be restored its factory specifications afterwards — altogether about a three-week job.