The analysis window of the Equalizer plugin shows the signal in a range of [-18 dB FS, 18 dB FS]. The lower bound of -18 dB FS is too high and can hide a lot of spectral content in the higher frequencies.

Here's an example of a saw wave that's played at A1:

As can be seen it looks like there is no spectral content above 1.5 kHz when in fact there is content up to 20 kHz.

One possible solution to this problem is to give the user the option to adjust the scale of the analysis window.

See #3530 for more details.