Masking as a compositional technique

[Acoustic Interloper]

While listening to the recording of my NYE performance I noticed a dynamic that I could not account for. I started out the piece playing Scrabble-to-MIDI until I placed enough Scrabble words to constitute a decent rhythm section, and then improvised over top of that using a Godin MIDI guitar through a Roland GR33 and some FX in Live.

What I noticed upon a later listen was that, when I lean on the guitar, most of the Scrabble-to-MIDI sounds except the strong percussive peaks seem to fade away, and when I stop playing the guitar briefly, they fade back in. It gives the impression that the Scrabble-to-MIDI "player" plays louder whenever I back off the guitar; but there is no player. During the times that I play guitar, it is just running a generation algorithm from the game state + a bunch of config parameters that I set prior to switching to guitar. There is nothing in Scrabble-to-MIDI that would account for this dynamic.

My son Jeremy reminded me about "masking." Musimathics Vol. I discusses two flavors as I recall. One is pitch based, so that if two different sounds have pitches that differ by a little, and one has significantly higher amplitude, it masks the other.

The second flavor is temporal, where a higher volume note will mask a lower volume one that occurs shortly thereafter. In fact Musimathics says that there is an established phenomenon where the later note, when higher in volume, can mask the earlier one, if they occur closely enough together, because it takes the human auditory system time to process the lower amplitude signal. If that processing is interrupted by the higher amplitude signal, the early signal is never heard.

I suspect that the first, pitch based variant of masking accounts for this shifting dynamic in the perceived amplitude of my rhythm section, which is really cool. The other possibility would have been a compressor in the stage that mixes these two instruments. I did have a compressor there, but it was shut off during the performance.

This particular case was an improvisational accident, but it would seem that one could plan and compose to take advantage of masking in such semi-automated performances, as well as strictly human performances.