A sub-synth reinforcing a bass can thin the low end when its waveform is out of phase with the bass fundamental

A sub-synth generating a low sine or triangle to reinforce a bass part overlaps the bass’s own fundamental frequency range. If the sub’s waveform is out of phase with the bass fundamental at that shared frequency, the two signals cancel rather than add — the combined low end becomes skinnier than the bass alone rather than bigger. Worse, the phase relationship between the sub oscillator and the recorded bass changes from note to note, so the low end is inconsistent: full on some notes, thin on others, and hard to balance. The fix is to clear space at the fundamental so the sub owns the low range cleanly — steep high-pass filtering (or a surgical notch) on the main bass to remove its fundamental — and/or to use a blending waveform such as a triangle or sine.

Examples

A sub-octave patch under a bass guitar sounds full at one note (constructive) but collapses at another a step away (destructive), because the fundamental and the synth waveform phase-shift note to note. High-passing the bass fundamental lets the sub own the low end consistently.

Assessment

Explain why adding a sub-synth can paradoxically weaken rather than strengthen the low end, why the effect varies note to note, and describe one technique to diagnose and correct it.