The Wikipedia page for the album is fantatic. The producer, Teo Macero, contributed like a musician. "Go Ahead John" has its own section. Here's just a snippet...

Davis's trumpet and McLaughlin's guitar parts were heavily overdubbed for the recording. The overdubbing effect was created by superimposing part of Davis's trumpet solo onto other parts of it, through something Teo Macero calls a "recording loop". Macero later said of this production technique, "You hear the two parts and it's only two parts, but the two parts become four and they become eight parts.

This was done over in the editing room and it just adds something to the music [...] I called [Davis] in and I said, 'Come in, I think we've got something you'll like. We'll try it on and if you like it you've got it.' He came in and flipped out. He said it was one of the greatest things he ever heard".

DeJohnette's drums were also manipulated by Macero, who used an automatic switcher to have them rattle back and forth between the left and right speakers on the recording. In his book Running the Voodoo Down: The Electric Music of Miles Davis, Davis-biographer Phil Freeman describes this technique as "100 percent Macero" and writes of its significance to the track as a whole, stating:

This doesn't create the effect of two drummers. It's just disorienting, throwing the ear off balance in a way that forces the listener to pay close attention. The drums cease to perform their traditional function. Jack DeJohnette's beats, funky and propulsive on the session tapes, are so chopped up that their timekeeping utility is virtually nil.

Macero has diced the rhythm so adroitly that we are not even permitted to hear an entire drum hit or hi-hat crash. All that remains are clicks and whooshes, barely identifiable as drums and, again, practically useless as rhythmic indicators. Thus, the pace is maintained by Dave Holland's one-note throb and the occasional descending blues progression he plays. The feeling one gets from "Go Ahead John" becomes one of floating in space.