Phase audibility
Audibility of phase distortion has been a subject of discussion, I wanted to be able to test it myself.
So I did this program to check :
– can you hear absolute phase invertion ? the first button changes the absolute polarity between normal phase and inverted phase
– can you hear phase distortion of bass cut-off : does the phase distortion of your bass speaker or of a highpass filter bring any audible artifact ? So I did a filter to simulate this low frequency amplitude and phase distortion and an allpass filter with phase distortion only. This phase distortion is also known as group delay. Just change the Q value and listen.
– can you hear phase distortion of loudspeaker filters : does the loudspeaker filter phase have any audible effect when you avoid any amplitude change, ie are low order filters better than higher order one ? To check this, I did a mid filter consisting of a lowpass and a highpass added together, so you have an amplitude near flat but with phase distortion only (it corresponds to an allpass filter : flat amplitude with phase changed)
Note : in the filter choice, LR stands for Linkwitz-Riley.
Some help can be found in the tips and FAQs pages
The best signals I found to show up phase problems are :
- bass group delay : try the sawtooth signal
- mid frequencies and crossover group delay : check with the triple tone (thanks to Zwicker and Fastl for this idea)
Note : the phase response of the low frequency "phase only" is not exactly the same as the phase response of "ampl+phase", it’s a rough approximation. Maybe, I’ll need to improve this.
Normal / inverted phase for mid filter
The HF phase is automatically set for the flattest amplitude response for LF+HF. And this phase is called "normal phase". So this normal phase for HF may be inverted compared to the phase of LF.
Next step (?)
I am not able (at the moment ?) to lower the group delay in the low frequencies, I’d like to ! But with my IIR filters, it would be acausal and not stable. I should use a FIR filter (as I do in Crossvolver and in The final cut) but I don’t have the tools yet to adjust those in real time.
Thuneau with its Arbitrator has a soft that does this (I haven’t measured it) and Goldumd also introduced the Leonardo project. The KH O500C loudspeaker incorporates such a group delay compensation.
Versions history
1.0 removed recorder, simplified input selection and cosmetic changes.
0.63 changed some texts and suppressed the buttons HP / LP only.
0.62 first version on the web