I use Eq Apo regularly, so I downloaded that RePhase, and it looks pretty complex. I don’t even understand how to do what you proposed or what would it do. Question – wouldn't applying any kind of filter change the frequency response?
An all-pass filter can change phase response without affecting the frequency response. This is one of the wonderful things about digital audio
To set up such a filter, go into RePhase and click on the "paragraphic phase EQ" tab. You can then enter your phase equalisation filters into the console at the bottom of the screen in much the same way you'd use a conventional paragraphic (amplitude) EQ, in other words by setting the frequency, Q, and magnitude (in degrees rather than decibels):
To "correct" a non-phase linear headphone (or any audio device for that matter), what you'd do would be to take the measured phase response and to then create an
inverse of it using these filter settings. (For example, if your measured phase response had a 90° peak at 1000Hz with a Q of 1, you would create a filter with a 90° dip at 1000Hz and with a Q of 1.)
But to do this correctly, you'd need to have an accurately measured phase response of the headphone or other device you were trying to correct. For some of the reasons I mentioned in my previous two posts, I'm not sure it would be valid to assume that the phase response of a pair of headphones measured on a HATS or similar test rig would match the phase response of the same headphones on your head.
Anyway, assuming for argument's sake you did have an accurate measurement, once you'd used RePhase to create the correction filter, you would move across to the "impulse settings" tab on the right and plug in your desired settings. In your case, I would begin with the default tap no. and FFT length of 16384 and 65536, respectively. I'd suggest selecting "Blackman-Nuttal" as the windowing function, and set optimization to "extensive" to -100dB. Then under format, select "24 (or 32) bits LPCM mono", and under sample rate, select whatever sample rate your playback system normally operates in.
Finally, select the desitnation directory where you want to save the filter and hit "generate". The filter will be saved as an impulse response in 24-bit WAV format (at whatever sampling rate you selected).
Next, go into Equalizer APO and add a new "Convolution (Convolution with impulse response)" filter, which you'll find under the "advanced filters" submenu. Hit the file icon on the filter and browse to select the WAV file you just generated in RePhase.
Assuming nothing went wrong, Equalizer APO will now convolve all audio with this filter.
However, like I said above, although this is how you would do it, I'm not sure it makes any sense given the uncertainty concerning the validity of any headphones' measured phase response vs its phase response on your head. My hunch would be that in low and low-mid frequencies, a non-specific measurement might be reliable, but not so in the higher frequncies. I reckon
@solderdude might have something interesting to say on this question...