Comment 5 for bug 1904624

We need to careful not to mix two topics. We have on one hand the loudness contour of a human ear.
This can be summed up as:
"You only hear the full dynamic of track at full loudness on a reasonable PA"

This is not the topic here!

Mixxx already has the Loudness effect, to compensate that during dinner time or warm up.

For waveform analysis we use a Bessel LP/BP/HP filter for calculating waveform at cross over frequencies of 600 and 4000 Hz. This has the issue that the LP and HP have open ends and are not limited to the Hi-Fi frequencies of 20 Hz bis 20 kHz

At high frequency, we have a natural limit due to the sample rate of 22 kHz that limits the data to the Hi-Fi Range. (We will suffer the same issue if one is using 192 kHz tracks, btw).

This is not the case at the low frequency, we are even able to put out a DC signal.
All PA-amplifier have a High-Pass filter usually with a cut of at 20 Hz that protect the circuits from high energy low frequency signals that are likely self destroying.

Some sub-woofer pretend to go down to 16 Hz, but that is IMHO more like a marketing trick than reality and serious measurement of a flat free-air responds curve.

tl;dr
We may consider to add a high-pass filter at 20 Hz to our waveform analysis to filter that out.
However I am in doubt that we have tracks that have frequencies below 20 Hz. If we assume that there are none, such a filter would be pointless.

Before putting work into that we need a real live example, else we will fix a phantom.