Does Phase Distortion/Shift Matter in Audio? (no*)

[Thomas_A]

The whole polarity thing is basically moot unless you have linear phase crossovers. Otherwise, it just exchanges one wrong phase response for another wrong phase response, shifted by 180deg.

isn’t crossover point the issue here? Putting it in the voice registrer100-400 Hz is a no-no but 2-4 kHz is no problem.

 

[audio2design]

isn’t crossover point the issue here? Putting it in the voice registrer100-400 Hz is a no-no but 2-4 kHz is no problem.

I would argue the issue is 200-1KHz, perhaps up to 1.5KHz, the area where the brain uses phase.

 

[Thomas_A]

I would argue the issue is 200-1KHz, perhaps up to 1.5KHz, the area where the brain uses phase.

But the effect we are talking about here is not related directly to phase per se but the impact of asymmetric signals and ear non-linearaties.

 

[audio2design]

But the effect we are talking about here is not related directly to phase per se but the impact of asymmetric signals and ear non-linearaties.

Potentially, but they need to be audible. Is the ear / auditory system symmetric?

 

[Thomas_A]

Potentially, but they need to be audible. Is the ear / auditory system symmetric?

The specific case of phase here is likely a special one and relates to fundamentals in the upper bass range combined with overtones causing asymmetry. I don’t think an all-pass at 3 kHz will have such effects on these types of bass notes.

 

[audio2design]

But the effect we are talking about here is not related directly to phase per se but the impact of asymmetric signals and ear non-linearaties.

Actually it was about roll off with bandwidth at either end of the spectrum ... at least to start.

 

[dc655321]

It is linear phase in most of the passband. Only at the frequency extremes where the response rolls off we see the corresponding minimum phase shift creeping in.

Ok, thanks.
I thought that is what you meant, but it was phrased in such a way that it sounded "absolute".
I know you know better...

 

[Deleted member 22141]

I think Amir needs to do an in-depth video about whether there is any real point to the High-Res game at all.

It seems like it has the potential to cause many problems for very small occasional benefits.

Paul tried and failed to explain what one of those benefits might be.

 

[Thomas_A]

Actually it was about roll off with bandwidth at either end of the spectrum ... at least to start.

Yes agreed. And this is not relevant with respect to audibility.

 

[Ingenieur]

1) Natural phase shift (minimum phase response): strictly folowing the frequency magnitude response, the so-called minimum phase response. Applies to electronics and amps in general, and single speaker driver.

2) Excess phase shift (allpass response): The typical case is the multiway speaker crossover. The individual drivers are minimum phase (with or without the corrective EQ applied) -- assuming that their centers of emission is aligned -- but the sum, the total speaker is non miminim phase. It has more phase than a single driver with the same frequency response, that's why it is called excess phase. When the centers of emission are not aligned, an addtitional delay comes into place that also gives specific additional frequency dependent phase shift (a constant slope of phase in a frequency reponse plot with linear frequency axis is a frequency group delay, that's the definition. If the group spans all available bandwidth, it's a pure time delay).
This is also called allpass response as an allpass does not alter magnitude frequency response which stays at unity (all frequencies are passed unaffected). Only the phase is altered.

3) Reflections and modes: This is something different, though related. Assume a simple floor reflection, a copy of the direct sound arrives a few ms later. This gives the typical comb filter pattern (cancellation notches). When the source is minimum phase, the overlayed response is also minumum phase (unless one single special case, when the reflection is an 100% exact copy in shape and level). This is not intuitive but correct. Assume you have the comb filter pattern with non infinite null, you can set up an analog notch filter bank with the same response and guess what, now the impulse response is the matching doublet as we would measure it. And if you apply the inverse EQ (a bunch of peaking filters) the single original impulse is showing up again.

The general rule: a transfer function is minimum phase when it can be inverted so that the product is flat FR and zero phase. You will see a lot of different definitions of what is mimimum phase and what is not, notably that reflections and modes are were not minimum phase... they are (unless for the single uninvertible case of a perfect reflection).

thanks, I get that

But are we taking about V vs I (phase angle) or an incident sound wave vs reflected (refracted or absorbed is moot)?

 

[Ingenieur]

My hybrid electrostats throw a remarkably flat or consistent phase in-room to the listening position at 10 feet.

The panel crosses to the dynamic woofer at 180Hz, so some discontinuity starts around that frequency.

This is both speakers playing, with no DSP active, and no trickery (windowing, whatever) with REW.


View attachment 134433

Add DSP and some of the delay (?) in the bass is reduced


View attachment 134434

How does that work?
Measured the direct vs reflected and applied a ratio?

Assume direct is 90 dB SPL and reflected is 10 does it do some sort of calculation?

90 at 0 deg and 10 what ever the TD is for that frequency converted to degrees.
Using 1,000 Hz T = 0.001 sec, and if the reflected arrives 20% later (20% longer path) or 0.0002 sec that is 0.0002/0.001 x 360 = 72 deg out of phase, then weights them since the reflected is -80 dB it only counts for 0.01% of the total so has very little effect.
Or some similar method.

50 Hz 1080 degrees is is 3 periods out of phase or 0.06 sec?

 

[Ingenieur]

Not quite, in our context. We are talking about the frequency response of the phase of a transfer function, not sine oscillators.

A typical allpass response of a crossover:
View attachment 134466
Magnitude is flat as should be, but phase goes from 0deg to -360deg. A second harmonic of a 422Hz fundamental gets shifted by 90deg from this allpass and that can readily be audible as it turnes the first waveform in my post #39 into the second.

let's use round numbers
442 Hz -90
884 Hz -180
Phase shift is 90 deg

but each of the f's current is only shifted relative to its associated instantaneous voltage.

if we allow the V to be zero which is fine since what that is showing relative phase shift from voltage.
S = V1 x (I1/90)* = V1 I1 / -90 VA
S = V2 x (I2/180)* = V2 I2 / -180 VA

Therefore the relative power phase angle is still 90. Regardless, instantaneous real P is not affected
P = cos (ang) x V x I W
So at f1 is the same (90)
So is P at the f2 (180)

The change is relative instantaneously but not temporal.

 

[amirm]

Bass guitar note attached, straight into ADI-2 Pro recorded by yours truly a moment ago.

There is only one file there. Where is the phase modified version to compare?

 

[Thomas_A]

A bit off-topic but is there any small cheap DACs with a 180° polarity switch at front available today? My first DAC, the Audio Alchemy DDE 1.0 had one, but the DAC broke down for some reason and it went to garbage.

 

[RayDunzl]

How does that work?
Measured the direct vs reflected and applied a ratio?

The author of REW is a member here.

https://www.audiosciencereview.com/forum/index.php?members/johnpm.1797/#about

 

[KSTR]

let's use round numbers
442 Hz -90
884 Hz -180
Phase shift is 90 deg

but each of the f's current is only shifted relative to its associated instantaneous voltage.

if we allow the V to be zero which is fine since what that is showing relative phase shift from voltage.
S = V1 x (I1/90)* = V1 I1 / -90 VA
S = V2 x (I2/180)* = V2 I2 / -180 VA

Therefore the relative power phase angle is still 90. Regardless, instantaneous real P is not affected
P = cos (ang) x V x I W
So at f1 is the same (90)
So is P at the f2 (180)

The change is relative instantaneously but not temporal.

Ahm, this is not about the phase relationship between current and voltage. It totally escapes me why you bring up this electrician's stuff.

 

[KSTR]

There is only one file there. Where is the phase modified version to compare?

You can make one yourself, using for example RePhase, if you really cared.

 

[Xulonn]

 

[Longshan]

A viewer of my videos and member he suggested that I do a video commenting on a video that Paul McGown did on audibility of phase shifts. Here is Paul's video which was really about a different question (why we need wideband amplifiers) but turned it into phase being an audible problem:

Here is my answer to him:

EDIT:

I knew I should have waited until the end of your video. You're referring to the phase of an individual sound wave; in other words, the absolute phase position of a sound. Of course you are right, the is no difference.

___________________________________________________________________________________________________________________________


Of course phase is an important electrical and acoustic thing and has relevance in countless situations. It is just that it should not be used to create myths and fear in audiophiles with respect to audibility in the context Paul and others are using.

I don't understand this video at all. I hear phase shifts all the time. It's a problem we are constantly dealing with when mixing music, because we are almost always introducing some amount of phase shift whenever we do almost anything to a sound (EQing, etc.). When you are doing a null-test you are literally hearing the results of a 180º phase shift. We also introduce phase shift on purpose to an extent when we are manipulating the stereo field.

I must not understand what you mean, because hearing phase shift is as common as a cup of tea in the world of sound engineering.

 

[Ingenieur]

Ahm, this is not about the phase relationship between current and voltage. It totally escapes me why you bring up this electrician's stuff.

That was my question which you answered with a dissertation.
Then why post plots which show the phase shift V vs I? Or discuss filters which are electrical devices?

If we are solely discussing room reflections unless the RT60 time is large and attenuation is small you will not discern it. In the bass region with 2 sources and if significantly out of phase and A/B compared you MAY hear it.
The original supposition is correct, you can't hear it unless the system is mis-configured so you can.