Not out of tune, but undecided - masters apprentices had an amp valve blow in the studio. Ended up sounding really good so they left it.

there's an Opeth song called Burden where he does an acoustic passage at the end and then de-tunes as it goes.

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>undecided - masters apprentices

That's a great track, wow! but I don't hear the amp valve blowing. Is it at the very end?

Sorry.. it happened before they started recording. So the whole song has the blown valve

Wow how did they do that you think? Someone playing the part while another person turning the tuning peg?

I believe so.