# How to do a spectral fade out?

I'd like to do a fade out of a sound in a few seconds, but in a "spectral way", with a special curve :

(here x-axis is time, y-axis is frequency from a few hz to 20khz).

All the part "to be removed" has to be removed !

Do you know how to do this ? (an EQ / simple IIR/FIR filter won't work for this, etc.)

• One simple option might be a leaky integrator. This is a first-order lowpass IIR filter that only has one parameter, $\alpha \in (0,1]$. You can sweep the parameter across a range of values as needed to adjust the cutoff frequency. Nov 14 '13 at 12:58