In chart genres, ‘Thou Shalt Mono The Low Frequencies’ is pretty much established wisdom, and with good reason: you typically get the strongest impression of bass from any set of stereo speakers if both their low-frequency drivers work in unison. Besides, our stereo perception’s pretty vague below about 100Hz, so why not go for maximum bass? Well, as it happens, that’s a question this production rather nicely answers.
What Twenty One Pilots have done is trade off some of their mono bass power for bass width by leaving a degree of stereo decorrelation (ie. out-of-phase elements) in the low end of the main bass synth. While the reliability of our stereo location perception reduces below 100Hz, out-of-phase stereo components in that region do nonetheless retain a good deal of subjective impact, as can be appreciated here — the bass of ‘Heathens’, while notionally placed centrally, seems to envelop you in a way that the bass in, say, Major Lazer’s 'Cold Water' can’t match. By combining this bass decorrelation with the strongly mono-incompatible fundamental frequency of the piano’s ostinato E, the producers have imbued the sound with a splendidly cinematic sense of warmth and width in stereo, but at a very acceptable cost in terms of mono compatibility: the recessing of a musically rather uninteresting piano note and the loss of a little mono bass solidity. The latter is no great shakes in a production that’s clearly aimed more at cinemas than nightclubs, as far as likely full-range end-user listening situations are concerned.