Iñárritu stated that the classical components come from the world of the play, citing the radio in Riggan's room and the show itself as two sources of the music.

[8] His reaction to writing a soundtrack using only drums was similar to Lubezki's thoughts of shooting the movie like a single shot: "It was a scary proposition because I had no point of reference of how to achieve this.

[11] Sánchez then waited until production moved to New York before composing more,[10] where he visited the set for a couple of days to get a better idea of the film.

[4][12] During these sessions the director would first talk him through the scene, then while Sánchez was improvising guide him by raising his hand to indicate an event – such as a character opening a door – or by describing the rhythm with verbal sounds.

[12][13] They recorded around seventy demos,[10] which Iñárritu used to inform the pacing of the scenes on set,[14] and once filming was complete, spliced them into the rough cut.

[10][15] Amusingly, this process was included in the film – the first sound in Birdman is in fact Sánchez asking Iñárritu a question in Spanish, followed by his detuning of the drums.

This meant Sánchez had to learn and match him exactly during the recordings in Los Angeles,[9] noting "Alejandro was very specific and he would watch the clip over and over again to make sure that you could not tell that it was not him that was actually producing the sound.

The drums were moved out onto the street, and people carrying mics a block away would walk towards and past Sánchez as he was playing, to coordinate the sound and image of the film without the need for post-production effects.

Sánchez had received a note from the award committee a day earlier explaining the decision, quoting rule fifteen of the 87th Academy Award Rules and writing they felt "the fact that the film also contains over a half an hour of non-original (mostly classical) music cues that are featured very prominently in numerous pivotal moments in the film made it difficult for the committee to accept your submission".

[18] One of the points raised was that the committee had incorrectly calculated the ratio of classical to original music, which after being clarified Sánchez thought he was "on really solid ground".