Measure gain at certain frequency

[juha_tp]

I'm working on a weighting filter and would like to adjust 0dB gain for combined filters (four first order HPFs and one biquad LPF which is implemented as 4th order filter) to be exactly at 1kHz. I know the gains for each filter stage @1kHz and when use these in coefficient calculation the resulting filter is other wise OK but, few hundreds of dB's below target gain 0dB at 1kHz (when not using the HPF gains it's only couple of dB's below target).

So, as a fix, I added a trim knob for to adjust the gain after filters just before output (dunno if it is a good place for it) so now output level is ~OK but, I would like to show (label) the exact gain present at 1kHz while adjusting so it can be accurately adjusted.

Are there any examples available for this type task (based on Ruby, DSP code, toolbox modules)?