30. Why does Band-in-a-Box® generate notes below low E (E2) on a MIDI bass part?

You can set the lowest bass note in the Band-in-a-Box® | Preferences(2) dialog. If you have set your lowest bass note to E2, which is the default setting, Band-in-a-Box® will not play any bass notes below E2, with one exception: Band-in-a-Box® occasionally produces a short low bass note (usually an octave below the root) to simulate a muted bass note on the third triplet of a walking bass line. These short notes don't get displayed in notation, but do get played.

Alyssa - PG Music