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Topic: is it even possible to hear "Phase distortion"? (Read 2455 times) previous topic - next topic
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is it even possible to hear "Phase distortion"?

I came across a dude who thinks he can hear phase distortions made by an equalizer. Putting aside differences in loudness of different frequencies, this means he should be able to hear differences made by an all-pass filter. I doubt he will prove it even if he could. But I am pretty sure this difference is impossible to hear if tested correctly (so, for example, signal after filtering doesn't clip, etc).
I tried to search the web a bit and could not find if anyone succeeded in detecting an all-pass filter by ear in a blind ABX test.
Should I immediately dismiss this dude as yet another placebo troll, or he might actually have golden ears?


Re: is it even possible to hear "Phase distortion"?

Reply #2
An EQ can theoreticaly add ringing with linear filters in the audible band. If anything this may be a possible distortion heard.
I didn't dig into this problem so i may be wrong.
Is troll-adiposity coming from feederism?
With 24bit music you can listen to silence much louder!

Re: is it even possible to hear "Phase distortion"?

Reply #3
I came across a dude who thinks he can hear phase distortions made by an equalizer. Putting aside differences in loudness of different frequencies, this means he should be able to hear differences made by an all-pass filter. I doubt he will prove it even if he could. But I am pretty sure this difference is impossible to hear if tested correctly (so, for example, signal after filtering doesn't clip, etc).
I tried to search the web a bit and could not find if anyone succeeded in detecting an all-pass filter by ear in a blind ABX test.
Should I immediately dismiss this dude as yet another placebo troll, or he might actually have golden ears?
I don't know about any particular EQ, but it's definitely possibly to hear phase distortion if it's sufficiently large. Taking an extreme example, imagine a system that has zero phase from 0 to 2 kHz, followed by a steep slope after that. It would basically mean that the HF get delayed compared to the LF. If you make that delay large enough (e.g. 100 ms), you're definitely going to hear it. I'm not sure where that threshold is. Similarly, if you have a stereo signal and you have different phase distortion to the two channels in the LF, then again you're going to hear it as a spatial shift in the stereo image. The sensitivity to phase depends a lot on the signal. If your signal is just two constant tones, then I don't think you can hear anything at all. OTOH, if your signal is made of clear/narrow impulses, then you want good phase response to avoid temporal smearing. It's all about whether the phase distortion changes the temporal shape of the signal.

Re: is it even possible to hear "Phase distortion"?

Reply #4
Also there is the possibility of bad caps (old electrolytic ones that dried as example) in the filters chain doing weird things with the signal. Transistor, ICs, diodes and resistors can also go bad and affect signal but its much less frequent at least in the audible range of frequencies.

Re: is it even possible to hear "Phase distortion"?

Reply #5
They say so over here:

Quote
Given the data provided by the above cited references we can conclude that phase distortion is indeed audible, though generally speaking, only very subtly so and only under certain specific test conditions and perception circumstances.
 
Impressive as the paper(?) looks like, I'm not sure about how qualified they are to draw that conclusion.
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Re: is it even possible to hear "Phase distortion"?

Reply #6
Well it's clear that it would be hearable if max delay difference is as big as 100 ms, but I think they talked about "regular" equalizers, so the delay of certain bands will be less than 5 ms or something like that.
They claim they can hear "any" phase distortion, and this is not possible AFAIK, but I'm not 100% sure.

Re: is it even possible to hear "Phase distortion"?

Reply #7
Impressive as the paper(?) looks like, I'm not sure about how qualified they are to draw that conclusion.
The article lists several papers which all present evidence, upon which that "conclusion" is derived. The "qualification" of the author is not relevant here, the evidence is. If "qualifications" matter, then note that Dr Floyd Toole agrees with the author. If/when audible, often subtle, preferences vary.
The OPs story is not based on any evidence, unless someone on the internet purportedly fooling about with an EQ qualifies.

cheers,

AJ

Loudspeaker manufacturer

Re: is it even possible to hear "Phase distortion"?

Reply #8
If the anomaly or filter or whatever is minimum phase, you can have quite a significant amount of what could be called "phase distortion" and it will likely be totally inaudible.  Any abrupt phase changes, especially those which change the shape of the signal, could possibly be heard at some threshold.  But then those systems will have excess phase and depending on the exact transfer function they could change many things which our ears are sensitive to - such as the impulse response.

Re: is it even possible to hear "Phase distortion"?

Reply #9
Quote
I came across a dude who thinks he can hear phase distortions made by an equalizer.
If the equalizer is set flat you shouldn't be getting any phase shift.   And, if it's not set flat you are expected to hear a difference.

Quote
this means he should be able to hear differences made by an all-pass filter. I doubt he will prove it even if he could. But I am pretty sure this difference is impossible to hear if tested correctly (so, for example, signal after filtering doesn't clip, etc).
All-pass filtering can make some peaks higher and some peaks lower, especially if the recording was highly compressed or limited, so it can cause sometimes cause clipping unless you reduce the volume.   So, that's something you'd have check for and or control-for by possibly reducing the volume of the original and the all-pass filtered copy.

 

Re: is it even possible to hear "Phase distortion"?

Reply #10
This is my OPINION based upon critical listening as part of my project...  So, take it with a grain of salt, but I do have some evidence as to the quality of my results...
First, phase itself on a sine wave is not detectable.  Phase differences between two sine waves of different frequencies (basically a timing difference) is almost specious in the long term, but in the short term -- there is an issue of timing causing different wave shapes.   Except in weird cases of complex combinations that end up creating significant impulses or similar -- moderate changes in phase are not generally audible.

There are some cases where phase (or more precisely -- fast changes in phase vs. frequency) become noticeable:

In my opinion, the major thing that the ears detect other than tones are 1) impulses as clicks and 2) timing differences between the events.
So, if a filter causes a significant difference in TIMING relationships in the signal, where impulses and time differences between components of the sound become noticeable -- then the effect of filter phase changes vs. frequency (which equate to timing) is noticeable -- esp at high frequencies.

So, if you have a near-impulse envelope of a high frequency tone, then if the timing relationship between that envelope and the signal are distorted, then the change in the timing relationships can sometimes be heard.  Also, if you have tones of different frequency whose timing of the envelope changes, then that can also be heard (and in the correct conditions, WILL be heard by perceptive people.)   An example of this situation would be modulated vocal sibilance.  (Effectively a fast modulated high frequency tone with a slower modulation mixing to produce a rather ragged signal.)

I have heard this manifest by sibilant vocals where the sibilance is modulated.  If a filter that deviates too far from linear phase is used, it can make the sibilance on the vocals sound worse or even bad.

On an ad-hoc basis - I have three kinds of low/high pass filters that I normally use to maintain a fairly consistent shape of the waveform so as to control the negative effects on sibilance.   1)  FIR linear phase filter, 2) IIR filter with Q=0.500, 3) two series IIR filters, one with Q=0.500 and the next with Q=0.707 at same cutoff frequency.  (Q=0.500 approximates a Bessel filter -- not so good for digital IIR filters, but still helps.)  A mix of Q=0.500 and Q=0.707 helps to maintain waveshape while still providing a sharper cutoff than just a 'soft' Q=0.500.

By following the above rules, I have been somewhat successful at controlling the sound of sibilant vocals and not to make the sound even more disruptive.

BUT, in GENERAL, the  hearing of music isn't strongly impacted by phase.  There ARE cases (as I mentioned above), where it SEEMS like maintaining a linear phase (or nearly so) can be helpful.

John




 
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