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

[KSTR]

And yes, this track IS dangerous. Use with caution. Main energy is at 60Hz, one cycle basically. I notice almost no effect of polarity inversion, btw.

 

[Anthony101]

 

[BlackH20]

I am no audio engineer, but does this review mean that we should immediately confine the £60 Audiophile Guide by Paul McGowan to the bin?

View attachment 134944

If you want a long sales book mainly on PS Audio and Paul (who is no audio engineer either), buck up; otherwise, save your hard-earned money.

 

[Compact_D]

If we assume that stereo image is 3D and contains distance information, then distance information may be distorted due to different phase at different frequencies.

It may be difficult or impossible to hear at the high frequencies where amp roll-off is occurring, but when I was designing cross-over filters (long time ago, though), I was using the test signal of a sweep frequency fixed point source that I recorded myself. If the sound source moved (and it often did) I was assuming speaker had a problem, as point was relatively static when played back through the single driver speakers.
Without any scientific proof, I was assuming this was caused by phase shift in the filter. Or is it all wrong?

 

[restorer-john]

I’m particularly grumpy today. So that has a bit to do with it.

That's funny. Made me laugh. Cheers. I get grumpy too.

 

[Andrew s]

Well, once you fully aware that there can be a systematic effect (and often is), you will also note it in normal recreational listening, assumed you have access to a polarity flip switch (many DACs have, SW players as well, or just use a plugin).

You have convinced me not to try these tests. I want to continue to listen to the music and not the system! Some while ago I decided not to train my listening for the same reason.

Thanks anyway regards Andrew

 

[restorer-john]

You have convinced me not to try these tests. I want to continue to listen to the music and not the system!

We all go through stages where you listen to the music, the system, the system, the system and then back to the music for a while.

It all boils down to whether the music is the reason for high fidelity gear existing in the first place, or the gear itself is why we have high fidelity equipment at all.

Chicken and egg stuff.

 

[Andrew s]

We all go through stages where you listen to the music, the system, the system, the system and then back to the music for a while.

It all boils down to whether the music is the reason for high fidelity gear existing in the first place, or the gear itself is why we have high fidelity equipment at all.

Chicken and egg stuff.

Pushing 70 and still far too much music to try to spend long on listening to the kit. I enjoy understanding the audio kit and phycoacoustics but risking my enjoyment no thanks.

Regards Andrew

 

[Tom Danley]

And yes, this track IS dangerous. Use with caution. Main energy is at 60Hz, one cycle basically. I notice almost no effect of polarity inversion, btw.

Just like a loudspeaker's impulse response, you do not see the low frequency components unless you FFT a longer window, there is significant output to and below 10Hz. Like i said too, often there is a difference in the sound but not clear one is "better" than the other.

 

[KSTR]

Just like a loudspeaker's impulse response, you do not see the low frequency components unless you FFT a longer window, there is significant output to and below 10Hz. Like i said too, often there is a difference in the sound but not clear one is "better" than the other.

Energy spectrum of the whole recording:

Even though the main peaks (which could go for nice kick drums ;-) are very sparse -- look at the peak to rms ratio of 37dB --, they still have the most energy over total time in the 60Hz region.
And yes, there is a very nice ULF rumble to well below 10Hz and thats probably dominated by the mic roll-off etc.

The point I was making is that extreme high peak energy centered around 60Hz is concentrated at only a few spots.

 

[Phos]

Is phase shift part of the reason why there isn't currently a way of testing audio gear with arbitrary signals? That there would be no way to differentiate phase shift from harmonic distortion?

If we assume that stereo image is 3D and contains distance information, then distance information may be distorted due to different phase at different frequencies.

3D... really depends on the microphone being used... And if a microphone was used. If all the instruments are just being recorded in mono and piped into a mixing board, probably not, apart from whatever the producer put there.

Distance is also pretty complicated, kinda have to get naval gaze-y for it, you use the ratio of direct vs reflected sound for distance sources, and the difference in volume for closer sources (this is why hard panning is so obnoxious in headphones), but the only way we have to determine distance when we have zero or limited environmental cues for what to expect is our friend the pinna. Nearby sources' sound waves are still more meaningfully round than more distant one, so they interact differently with our pinna... Which is HRTF again!

It may be difficult or impossible to hear at the high frequencies where amp roll-off is occurring, but when I was designing cross-over filters (long time ago, though), I was using the test signal of a sweep frequency fixed point source that I recorded myself. If the sound source moved (and it often did) I was assuming speaker had a problem, as point was relatively static when played back through the single driver speakers.
Without any scientific proof, I was assuming this was caused by phase shift in the filter. Or is it all wrong?

Moved how? Pure tones are going to sound as thought they're coming out of the driver tasked with the bandwidth that tone occupies, apart from tones where they have considerable overlap.

 

[BrEpBrEpBrEpBrEp]

Is phase shift part of the reason why there isn't currently a way of testing audio gear with arbitrary signals?

Isn't there? Null-tests, for example, will show any deviation between any two signals.

 

[Phos]

Isn't there? Null-tests, for example, will show any deviation between any two signals.

Right, you can null test amps, like that famous story about Bob Carver... But I would expect two signals with different phase shifts to not completely null out.

 

[BrEpBrEpBrEpBrEp]

Right, you can null test amps, like that famous story about Bob Carver... But I would expect two signals with different phase shifts to not completely null out.

Yes, but that doesn't stop there from being a method of testing gear with arbitrary signals. Anything that doesn't null is a difference, by definition. That was the only part of your post I was replying to.

Whether the difference is audible, and if so how much - those are separate questions.

 

[Phos]

Yes, but that doesn't stop there from being a method of testing gear with arbitrary signals. Anything that doesn't null is a difference, by definition. That was the only part of your post I was replying to.

Whether the difference is audible, and if so how much - those are separate questions.

Ah I see, I meant in the context of a device akin to an AP analyzer, if you could play an arbitrary signal (music, for example) through one and get a THD/IMD number out of it.

 

[KSTR]

@Phos, you may have missed the ground-breaking DeltaWave feee software from our fellow member pkane.
With arbitrary signal THD/IMD has no meaning but you can of course analyze the difference signal in many ways.
Actually, tiny difference in phase and magnitude (==different frequency responses) is what usually dominates the difference and hence we are seeking ways to factor them out for meaningful Null tests (exposing distortion and any other error signal).

 

[KSTR]

3D... really depends on the microphone being used... And if a microphone was used. If all the instruments are just being recorded in mono and piped into a mixing board, probably not, apart from whatever the producer put there.

You can place mono source signals aynwhere into the 3D space with a number of means, one well known is called Q-Sound.

 

[Francis Vaughan]

Absolute Polarity.

Ah well. I made a mess of that one.
Sincere apologies to @KSTR and @restorer-john.
I did say I was especially grumpy.

I've been labouring reading on the phone the last few days, and just back with the laptop. Trying to catch up.

Still wish people would use polarity and not phase to describe polarity. Use of phase instantly gets us into all the other truly phase based questions.

 

[restorer-john]

I've been labouring reading on the phone the last few days, and just back with the laptop.

That totally explains it. There is nothing more frustrating than reading, or typing anything remotely technical on a phone screen. I refuse to do it.

It's a mush of predictive text, corrections I didn't ask for, big man fingers, missing characters, etc. Even a laptop keyboard is bad enough.

Go retro, get yourself an IBM 'clicky'!

In a similar vein, did you know you can connect a normal bluetooth keyboard to your phone and type like an absolute boss? A member here told me that.

 

[Francis Vaughan]

That totally explains it.

Not really. Digging my heals in and misremembering old papers. I felt sure I remembered the conclusions of the Lipshitz paper properly, but I didn't.