Next time you are at a Bath International Music Festival or Mozartfest concert, spare a thought to the hours of behind-the-scenes work that goes into tuning the piano before Pierre-Laurent Aimard, Alfred Brendel or anyone else actually sits down to play.

A new film which comes to Bath next month is the story of one unsung hero of musical perfection.

What you need is perfect pitch, steady-handed precision, unwavering patience and an abundance of passion – meet Stefan Knüpfer, the man behind some of the world's greatest pianists, whose story is uncovered in fascinating feature film Pianomania.

As Steinway & Sons' master tuner in Vienna, Stefan Knüpfer spends his days beneath the beautiful veneer of grand pianos, lovingly making tiny adjustments to the wall of hammers and labyrinth of strings in pursuit of the perfect sound.

Pianomania shows Knüpfer working alongside internationally-renowned concert pianists including Lang Lang, Pierre-Laurent Aimard and Alfred Brendel, revealing his pivotal role in realising the vision of each virtuoso as they strive for musical perfection in every performance.

Central to the film is the year spent preparing Pierre-Laurent Aimard's recording of Bach's Art of Fugue. With his contagious charm and quiet humour, Knüpfer works closely with Aimard to identify the right instrument and achieve that elusive perfect tone.

One of the challenges for the filmmakers was in ensuring cinema audiences could appreciate the very fine alterations to the sound and tonal quality undertaken by Knüpfer.

They achieved this by recording it in Dolby surround sound using 90 separate sound tracks.

Shot in high definition with fascinating rehearsal and music recording footage cameras are rarely allowed to capture, Pianomania reveals the art, the science and the passion behind the search for musical perfection.

The film is at the Little Theatre from August 22 to 24.