What disappears in mono and why
Mono sums left and right. Opposing phase relationships can partially cancel; width by itself is not the problem.
Diagnosis
- Toggle mono at matched output level.
- Watch correlation while listening to the element that changes.
- Identify whether loss comes from delay, polarity, modulation or stereo synthesis.
Decision
- Keep critical low-frequency anchors coherent.
- Reduce problematic side content rather than collapsing the whole mix.
- Check on headphones and speakers because perception differs.
Measurement boundary
Correlation helps locate risk; the audible mono sum decides whether that risk matters.
Common failure: A correlation value near +1 is not automatically better; it can simply mean narrower content.