“People either ask ‘why’ or ‘how’,” Pat Metheny told the Barbican audience last night when he unveiled his extraordinary Orchestrion robot orchestra. “Let’s say the ‘why’ is between me and my shrink,” he joked.

Clearly his most ambitious project to date the banks of instruments – drums, percussion, tuned bottles, marimba, vibes, player pianos and more – were lined up behind him on the stage like some kind of sinister mutant musical cult. Controlled by Metheny by foot pedals and a system of hydraulics and solenoids the concept is an extension of the player piano and slightly unnervingly the instruments all look as if they are playing themselves, the vision of some mad inventor.

Metheny played solo to start with before unveiling the Orchestrion from behind a curtain which drew gasps from the audience. He played the suite of music from his new album also called Orchestrion in its entirety but in a different order with some extra earlier material including the delicate ‘Always and Forever’ from 1990s album Secret Story. The highlight of the new album is arguably the ballad ‘Soul Search’ which in many ways fits with the Secret Story style but all the material is strong and memorable.

Occasionally Metheny left the robot orchestra to play without him which tickled some in the audience. But its limitations lie, unlike a proper band, in that it accompanies Metheny rather than actively takes a solo or develops what he is building and rhythmically it lacks the vitality of a live drummer and percussionist. Dynamics, too, I think are an issue with the technology. But nonetheless the Orchestrion is a great achievement and caused few problems for Metheny who frequently switched guitars although at the end the gremlins set in and Metheny had to settle instead for his trusty guitar. The concert was a little too long, the music from the album plus the introductory material from his Metheny/Mehldau album was probably enough. But clearly the tour is a huge experiment and Metheny deserves enormous admiration for the work that has gone in to developing the orchestrion. You’ll never see anything like it.

Stephen Graham