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

audio2design

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KSTR,


I don't see that as a typical crossover response at all, not at the finished speaker. Do you have phase measurements of a completed speaker. A designer is not going to "miss" so called phase inversions as it would cause quick drop off all but where the frequency alignment is, but that does not happen as the electroacoustic output of the driver and crossover is well down in magnitude.
 

Bullwinkle J Moose

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KSTR,


A designer is not going to "miss" so called phase inversions as it would cause quick drop off all but where the frequency alignment is, but that does not happen as the electroacoustic output of the driver and crossover is well down in magnitude.

A "designer" may not miss it, but the person doing final assembly for Klipsch just "might"

Start video at 21 minutes and 8 seconds >
 

KSTR

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What? I thought you said it was guitar string or something. I am not interested in test tones. Those are already in literature.
Bass guitar note attached, straight into ADI-2 Pro recorded by yours truly a moment ago.
Attack phase:
1623154213807.png

Apply a 90deg phase shift between fundamental and the 2nd harmonic will make it an asymmetrical waveform.

After 500ms (still settling):
1623154282106.png

(similar)
The spectrum here:
1623154989523.png

Fundamental and 2nd at almost same level, 3rd++ further down.

After 2s (steady state region):
1623154409655.png

Phase relationsships have settled by now and a nicely asymmetrical waveform is formed. This will sound different with flipped polarity (or a 180deg phase shift between the components), and with a 90deg offset in either direction it will look like the previous section and thus is immune to inversion but not to 90deg phase shifts.

And the spectrum at this point:
1623154508221.png

2nd has lost some level but 3rd++ are way down now.
 

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KSTR

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I don't see that as a typical crossover response at all, not at the finished speaker.
It is a typical crossover response, the excess phase is isolated because that is what we are after here. Showing a full response with its minimum phase roll-offs at either frequency ends plus the usual ripple would just confounds things.
 

daftcombo

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Oh, well that's something else entirely and would cause the delay effect I described, but in reverse. The body of the drum would be first, the attack would follow.
The effect was like a "wobble" sound. In fact, it took a lot of phase rotations for me to be able to hear it without a doubt. But perhaps +360° could be sufficient for some people under certain conditions. Not +10° though.
 

kevin1969

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It matters when there phase is a phase shift is RELATIVE to another signal (when the sub and regular speaker both reproducing the same frequency).

When I upgraded My bookshelf speakers from Klipsch RP500s to REL M16s they didn't quite have the same punch in the low end and I couldn't figure out why. Then it dawned on me that there's a switch on the back of the sub for phase and that's exactly what it was.
 

Thomas_A

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The sound, when inverted or all-passed, change in timbre in certain bass notes. All known in the literature as well as far as I know. In room however, effects are subtle or inaudible. And how do I know which is the correct phase of the recording itself?
 

KSTR

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And how do I know which is the correct phase of the recording itself?
Some recordings, mostly classical/jazz with only very few mikes used (preferably just a stereo main mic) reveal their polarity when looking at trumpet/trombone waveforms which tend to be asymmetrical. There are lists on the internet where (alleged) polarity of many recordings is tabulated, and many labels have consistent settings, for example Deutsch Grammophon is consistently inverted polarity.

Other stuff, multi-miked pop/rock with arbitrary amounts of processing or non-acoustic instruments there is no correct polarity to speak of for the individual source tracks, let alone for the total mix.

In the end, assumed it makes a difference to you at all, choose the setting that sounds better to you in whatever regard (timbre, soundstaging, etc).

There is no standard as far as recording practice goes, which just shows it is really a minor issue only. Sound changes are subtle but not non-existent.
 

Thomas_A

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Some recordings, mostly classical/jazz with only very few mikes used (preferably just a stereo main mic) reveal their polarity when looking at trumpet/trombone waveforms which tend to be asymmetrical. There are lists on the internet where (alleged) polarity of many recordings is tabulated, and many labels have consistent settings, for example Deutsch Grammophon is consistently inverted polarity.

Other stuff, multi-miked pop/rock with arbitrary amounts of processing or non-acoustic instruments there is no correct polarity to speak of for the individual source tracks, let alone for the total mix.

In the end, assumed it makes a difference to you at all, choose the setting that sounds better to you in whatever regard (timbre, soundstaging, etc).

There is no standard as far as recording practice goes, which just shows it is really a minor issue only. Sound changes are subtle but not non-existent.

Do you have any links to such lists?
 

UliBru

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There are many loudspeakers with minimumphase crossovers where some of the drivers show up an inverted polarity. Intended by the designer to achieve a nice response. So it is also difficult to talk here about absolute polarity.
 

audio2design

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It is a typical crossover response, the excess phase is isolated because that is what we are after here. Showing a full response with its minimum phase roll-offs at either frequency ends plus the usual ripple would just confounds things.

No, the full response, including the drivers, is what is needed to properly assess what is happening.

You appear to be blending two electronic cross-over responses (say a high pass and a low pass), but ignoring that that connects to real drivers and that is both an electro-acoustic and mechanical (placement) aspect of the completed system.
 

KSTR

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No, the full response, including the drivers, is what is needed to properly assess what is happening.

You appear to be blending two electronic cross-over responses (say a high pass and a low pass), but ignoring that that connects to real drivers and that is both an electro-acoustic and mechanical (placement) aspect of the completed system.
No, I always show effective acoustical behavior, the combined response. Everything else (like electrical only) is moot, obviously.

You may look at any published phase response and see the same underlying excess phase, just that it is a bit buried in the normal minphase response:
1623162313490.png

(as an aside, here you have the additional problem of where to set the reference point)
The crossover in this two-way is at ~2.5kHz or so, and its excess phase contribution is the 360deg rotation can be spotted in the 1..10kHz span. The rest of the phase in the low-mid/bass range is the minimum phase contribution, associated to the 6th order of the bass roll-off.
 
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magicscreen

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And how do I know which is the correct phase of the recording itself?
This is the MAIN problem for High Fidelity.
We never know it has high fidelity to...what? We do not know the original recording.
So you can use only measurements.
 

KSTR

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There are many loudspeakers with minimumphase crossovers where some of the drivers show up an inverted polarity. Intended by the designer to achieve a nice response. So it is also difficult to talk here about absolute polarity.
Sometimes the adjacent driver has to be inverted like in any N-th order Linkwitz-Riley XO with N=2,6,10,... with aligned acoustic centers.
But often designers add another inversion to compensate for the tweeter being 1/2 wavelenght closer to the listener at the XO frequency, to get "matching phases". This is incorrect in that it creates non-coherent output from the drivers, widening time duration of a shaped sine burst "blip" at the XO.
 

KSTR

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This is the MAIN problem for High Fidelity.
We never know it has high fidelity to...what? We do not know the original recording.
So you can use only measurements.
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.
 

audio2design

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The whole polarity thing is basically moot unless you have linear phase crossovers.


Something that we agree on :) .... I ditched passive for main listening ages ago. You can never do with passive components what you can with DSP. Another benefit is that by separating the processing for each driver, you can decimate the signal to a lower sample rate for the woofer which makes the signal processing much less compute intensive.
 

johnp98

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Much like @KSTR has said already. However, I would like to add one major difference when it comes to DSP/DRC and the use of FIR filtering especially at low frequencies in rooms. Unlike "most" DSP/DRC software for rooms, Acourate, Audiolense and Focus Fidelity (plus Denis open source DRC) provide excess phase correction at low frequencies. Which I contend is audible in the sense of the bass response not being clear sounding, aside from regular room modes.

Based on my testing and listening of DSP/DRC products over the past 10 years, there are very few software products that actually do this right and can produce the result you see above. While FIR filtering may be too processor intensive for AVR's and PrePro's (aside from the DSP chip limitation of how large a FIR filter can be hosted), a low power PC like an i3 2 GHz processor works just fine.

Pro tip: if you want the very best bass response from your system, use DSP/DRC software that is capable of providing excess phase correction at low frequencies.

Thank you for the very detailed reply and information!
Does Dirac do a reasonable job on the low end (I think I already know the answer, as they want low latency and thus probably don't have nearly enough taps for the low end)?
Do you or anyone have experience with rephase?
As I am looking for free / open source DRC and for whatever reason rephase seems less intimidating that the Denis open source DRC... or maybe I just need to find the right guide for the Denis DRC.
 
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