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Audibility of allpass phase distortion (test)
Audibility of allpass phase distortion (test)
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View Poll Results: Can you hear a difference between the test files?
YES 3 42.86%
NO 4 57.14%
Voters: 7. You may not vote on this poll

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Old 5th October 2018, 08:10 AM   #1
PMA is offline PMA  Europe
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Default Audibility of allpass phase distortion (test)

Allpass circuits are the circuits with flat amplitude response but various phase response. They are usually used as phase shifters, crossover circuits etc. They modify time response though keeping flat amplitude frequency response. It is generally considered that in audio their effect is inaudible. One of many links supporting allpass inaudibility is Phase distortion written by a man who has done a great work in audio during his life.

IME under certain conditions, depending on time duration and signal shape, the allpass phase and time distortion may become audible. I have prepared an experiment to compare 2 files, generated in LTSpice. Input signal is a train of 10 rectangular impulses of 10ms width repeated every 100ms. The test signal duration is 1s. It passed through inverting opamp with gain 1 phaser circuit with opamp, three 10k resistors and 100nF capacitor

Test wav files from both circuits were prepared.

Attached one can see the test phaser circuit (simple inverting amp for the test built just by omitting the capacitor in the phaser), amplitude and phase plots of the phaser and inverting amp, time plot from the test wav files and finally the test files in the phaser1.zip file.

Please try the test files and tell me if you can hear the difference. Foobar ABX result or protocol would be appreciated, I am attaching my result with headphones.

A poll with 14 days duration is attached as well.
Attached Images
File Type: png nophaser.PNG (53.7 KB, 270 views)
File Type: png phaser_circ.PNG (9.7 KB, 266 views)
File Type: png nofilt.PNG (31.5 KB, 268 views)
File Type: png allpass.PNG (34.1 KB, 271 views)
File Type: png phaser_ABX.PNG (38.4 KB, 270 views)
File Type: png phaser.PNG (60.2 KB, 53 views)
Attached Files
File Type: zip phaser1.zip (4.2 KB, 18 views)

Last edited by PMA; 5th October 2018 at 08:21 AM.
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Old 5th October 2018, 01:20 PM   #2
turk 182 is offline turk 182  Canada
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damn can't do the test because of mediaplayer issues!
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Old 5th October 2018, 01:28 PM   #3
PMA is offline PMA  Europe
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Do you need a stereo version of the test files? The posted one is mono.
Anyway, I am attaching a stereo version.
Attached Files
File Type: zip phaser1_stereo.zip (7.7 KB, 14 views)

Last edited by PMA; 5th October 2018 at 01:37 PM.
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Old 5th October 2018, 01:59 PM   #4
turk 182 is offline turk 182  Canada
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no i think it's an issue of the right codec my computer is ancient still running xp
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Old 5th October 2018, 02:09 PM   #5
PMA is offline PMA  Europe
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It is tested on XP as well. Works normally with Foobar, for example. Try the stereo version above, it might work for you. The issue might also be that the file is short (1s) and mediaplayer cannot play it.

Edit: just found that AIMP3 cannot play it. Regardless length and/or mono-stereo.

Last edited by PMA; 5th October 2018 at 02:16 PM.
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Old 5th October 2018, 02:34 PM   #6
bozoc is offline bozoc  Croatia
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With headphones.
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Old 5th October 2018, 03:53 PM   #7
Davey is offline Davey  United States
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You're generating an extreme case here. I can hear the difference, but it's slight.

Here's a quote from many years ago: (Maybe you'll recognize it.)

"It turns out that, within very generous tolerances, humans are insensitive to phase shifts. Under carefully contrived circumstances, special signals auditioned in anechoic conditions, or through headphones, people have heard slight differences. However, even these limited results have failed to provide clear evidence of a 'preference' for a lack of phase shift. When auditioned in real rooms, these differences disappear.."

Dave.

Last edited by Davey; 5th October 2018 at 03:56 PM.
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Old 5th October 2018, 04:28 PM   #8
lcsaszar is offline lcsaszar  Hungary
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I would be more interested in some good acoustic recording (chamber music, jazz combo) processed through an all-pass filter, compared with the original.
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Old 5th October 2018, 04:34 PM   #9
454Casull is offline 454Casull  Canada
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Can you do these with piano/percussion samples instead?
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Old 5th October 2018, 07:22 PM   #10
PMA is offline PMA  Europe
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I agree that this is quite an extreme case and yes Dave, I know the statement that you have quoted.

I should be able to prepare a music sample through an allpass transfer function, give me some time, please.
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