Why do vocal harmonies of older songs sound have that rich, “airy” quality that doesn’t seem to appear in modern music? (Crosby Stills and Nash, Simon and Garfunkel, et Al)

Question

I’d like to hear a scientific explanation of this!

[Example song](https://youtu.be/C7HP9Xkim9o)

I have a few questions about this.
I was once told that it’s because multiple vocals of this era were done live through a single mic (rather than overdubbed one at a time), and the layers of harmonies disturb the hair in such a way that it causes this quality. Is this the case? If it is, what exactly is the “disturbance”? Are there other factors, such as the equipment used, the mix of the recording, added reverb, etc?

EDIT: uhhhh well I didn’t expect this to blow up like it did. Thanks for everyone who commented, and thanks for the gold!

In: Physics

Answer 1

Overdubbing was common even in this era; in fact, the effect here is produced by multitracking, a form of overdubbing in which multiple takes of the same part by the same vocalist(s) are overlaid and bounced to a new track. What you were told about acoustic disturbance isn’t totally inaccurate, as the perceived effect itself comes from the constructive & destructive interference of the overlaid waveforms, but this doesn’t require that they interact in the air, which you can test for yourself just by graphing any two simple waveforms and then graphing their sum. The same waveform summed with itself will produce the same waveform but with twice the amplitude/volume (1+1=2 (constructive)), while a waveform summed with its inverse will produce silence (-1+1=0 (destructive)). Where no two takes of a part will ever be identical, the multiple waveforms interact with one another in such a way as to create a complex pattern of interference, reinforcing & attenuating certain frequencies in a non-fixed way, which we perceive as this ‘airy’ quality you describe, and which cannot be produced quite the same just by processing the signal with a unison or chorus effect as is common today.