A new video was posted on Reddit that shows how Sigma's emote changes based on the song Lucio is playing. The video checks speed, healing, and even amps it up and the pitch changes slightly each time. Overwatch is full of small details and this one is no different. Speed increases the pitch and amp it up takes it a step further.
Sigma's Maestro emote, which is a part of the Sigma Maestro Challenge is the only emote that changes in pitch. It is also unclear if only Lucio is able to incite this change because he is a musical character himself. Both Orisa and Mercy are capable of similar buffs so perhaps they too can influence the pitch of the emote.
Players looking to get the emote should act fast because it will only be available during the challenge which ends on July 27. Overwatch players that are interested in the music should also check out the "Cities and Countries" soundtrack that was released the day before the challenge began.