When I play WAV file 48 kHz 16 bit, with HRTF plugin is abit slower than without the HRTF plugin. I have to add soundtouch plugin to speedup around 8.76% to "almost" match the original. I try to convert source file into 2 wavs(one with, and one without hrtf), I found different file sizes (and tempo )

I haven't test it with 44.1 kHz source.

Do you guys experience this ?

Prolog: I don't use HRTF and doesn't know any specs of it, but...

I guess HRTF can only use 44.1 kHz as max or sth. like that.
48 kHz = ( 100 + 8,85 ) % of 44,1 kHz
If you have 48000 samples per second and HRTF only takes 44100 of it to give you that as a second of music, you get less than you need to listen to the file in normal speed.
At least you have to speed up to press more samples into a second.

edit: inserted if-clause