Masking the varying amplitude 440Hz tone with a 400 Hz tone?

Question

When masking the varying amplitude 440Hz tone with a 400 Hz tone, the masking effect was
not equal for equal amplitudes before and after the peak had passed. Why was that?

Answer 1

My guess would be phasing.

Before the peak, the 400 Hz signal is leading; after it is lagging. Therefore, the "shape" of the net amplitude is asymmetric about the peak.

You could probably demonstrate this for yourself in an Excel spreadsheet using the "chart" function. Create a table of values of theoretical amplitude for a 400 Hz and 440 Hz wave (be sure to use a fine enough "time slice" - 1/8000th of a second or so). Sum these two values and chart them.

A picture is worth a thousand words...