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Understanding Jitter in Digital Audio: Measurements and Listening Tests

amirm

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Yet another video, this time on topic of jitter. It is a tough topic to cover and I had to do it over and simplify it from my first "take." Hopefully you can follow it. :)


Article: understanding digital audio measurements: https://www.audiosciencereview.com/...derstanding-digital-audio-measurements.10523/ SPL

Phonitor X Review (DAC & Headphone Amp): https://www.audiosciencereview.com/...pl-phonitor-x-review-dac-headphone-amp.21114/

Julian Dunn on Jitter:
https://www.aes.org/e-lib/browse.cfm?elib=6111
https://www.aes.org/e-lib/browse.cfm?elib=6772 Jitter Audibility: https://www.aes.org/e-lib/browse.cfm?elib=8354
 

Blumlein 88

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This is one of your videos I'll not watch. I'm sure it is a good video. I'm just sick to death of the jitter bugaboo. I've sometimes called it the demon of digital audio. So much has been written about it, and it has been fussed over and used as a possible excuse for so much useless BS, stupid audiophile design choices, and just general wrong-headedness it is appalling. Yet it is darn close to never being an issue which is audible.

EDIT:so with some time to kill, I did watch it. Usual good work by Amir. And as he concludes, jitter is a solved problem, not the digital demon.
1615277886109.png
 
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roog

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Thank you @amirm that was nicely presented, I am sure that I was taught it many years ago but is long lost in the further reaches of my mind.
I may have to watch this a few times for it to sink in a little more.

Perhaps you can correct me if I have this wrong, so we are saying:

That with most DACs, jitter does not manifestly impact on listening experience?
Jitter is caused by very small inconsistencies in the DAC clock edge timing between clock pulses?

And a question if I may:
Are artefacts due to jitter caused by timing errors in the incoming digital signal i.e. the edges of the signal stream are not consistent?

Cheers
 

Koeitje

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Just a notion: Many so called audiophiles seems to be very troubled by digital cables creating jitter.
And none of the manufacturers offering low-jitter cables actually offer measurements showing they lower jitter.
 

adamd

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@amirm
Thanks for the video which is interesting. Please forgive me if I am being stupid or misunderstanding, but I nearly spat my tea out at 15:15- it seemed as though your were describing the jitter sidebands above and below the 12khz test signal, ie at higher and lower frequencies than the test tone, as being before and after the signal. You specifically refer to audio masking of spuria "after" a signal but not before. It seemed to me that you were mixing up the time and frequency domains ie mixing up temporal masking with the masking of adjacent frequencies. That said obviously you know more about this than I do.
I appreciate that I may have got the wrong end of the stick, and wondered whether you meant "before" as in "at a lower frequuncy and therefore appearing "before" when reading left to right on a graph" but I am not aware that frequency masking only works if the masking frequncy is higher, so I can only assume that you were referring to temporal masking. But I don't see how it could be temporal masking, becasue as you yourself observe the effect of jitter is not directly perceived as timing uncertainty but as the frequency sideband effect.

Obviously I claim no expertise here, and apologies if I have misunderstood. Can you help me out here.
 

neilb

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Thanks, Amir. Really enjoying the digital audio processing primers. For anyone interested in learning about this stuff in a structured yet accessible way can I suggest a visit to Akash Murthy's YouTube channel starting with:

Signal Paths - Digital Audio Fundamentals

The 2nd video in the series, Sampling Theorem - Digital Audio Fundamentals, totally nails the reason that 44.1kHz was chosen as the sampling frequency for Red Book audio (CDs) and presents Nyquist Theorem in a manner that even the most die hard subjectivist will derive some appreciation from.

The videos are beautifully animated and presented in a clear and non-patronising manner and serve to give a solid foundation to the concepts that Amir has been discussing. Absolutely Ace :)

Akash also links to some short presentations on Psychoacoustics by Professor Susan Rogers at Berklee which explain how our ears interpret consonance and dissonance which Amir has touched on in previous videos, also very enlightening.
 

roog

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Thanks, Amir. Really enjoying the digital audio processing primers. For anyone interested in learning about this stuff in a structured yet accessible way can I suggest a visit to Akash Murthy's YouTube channel starting with:

Signal Paths - Digital Audio Fundamentals

The 2nd video in the series, Sampling Theorem - Digital Audio Fundamentals, totally nails the reason that 44.1kHz was chosen as the sampling frequency for Red Book audio (CDs) and presents Nyquist Theorem in a manner that even the most die hard subjectivist will derive some appreciation from.

The videos are beautifully animated and presented in a clear and non-patronising manner and serve to give a solid foundation to the concepts that Amir has been discussing. Absolutely Ace :)

Akash also links to some short presentations on Psychoacoustics by Professor Susan Rogers at Berklee which explain how our ears interpret consonance and dissonance which Amir has touched on in previous videos, also very enlightening.

Excellent videos @neilb good shout!
 

Asinus

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Just a notion: Many so called audiophiles seems to be very troubled by digital cables creating jitter.
It seems like a belief originating from a malicious use of a misconception. When a cable does not have enough bandwidth for a square pulse it will spread the squares which in turn creates interference with the adjacent pulses and that can cause bit flips. Sometimes this effect is also called jitter (in communications theory it is called inter-symbol interference, jitter is mainly the timing variation).

If you heed the original Nyquist criterion (the one dealing with telegraphic transmission) your cable must have at least twice the bandwidth of your signaling rate to avoid interference and see the cable as a "flat" channel modeled by a simple gain loss, but when ISI is present and your signal to noise ratio is good there are a lot of digital techniques that will work better than a thousand dollar cable.
 

thefsb

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Superb. I needed this.

At 12:10 you say, "You can see there's a lot more activity now here than there was." 1) No, I can't. With a few exceptions, the red looks to have a lower noise floor than the blue. So what am I supposed to be looking for? 2) What does "activity" look like? 3) Aren't we concerned instead about presence of tones in the output that aren't in the input, i.e. distortion products?

1615319970966.png
 
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amirm

amirm

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You specifically refer to audio masking of spuria "after" a signal but not before. It seemed to me that you were mixing up the time and frequency domains ie mixing up temporal masking with the masking of adjacent frequencies.
There are similar effects in both domains. Unless I say otherwise, I mean perceptual/frequency masking. I hope I did not say temporal masking in the video. Did I?

To be clear, jitter is a timing effect but its audibility is determined in frequency domain. It is millions of times faster than any effect in timing domain.
 
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amirm

amirm

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At 12:10 you say, "You can see there's a lot more activity now here than there was." 1) No, I can't. With a few exceptions, the red looks to have a lower noise floor than the blue. So what am I supposed to be looking for? 2) What does "activity" look like? 3) Aren't we concerned instead about presence of tones in the output that aren't in the input, i.e. distortion products?
Yeh, I got bamboozled by one-take, live video production! :) The first time I recorded the video, it produced the same high levels that I showed in the review of the SPL:

index.php


Because the spiked are due to whatever noise spectrum there is on USB, it comes and goes.
 
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amirm

amirm

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That with most DACs, jitter does not manifestly impact on listening experience?
Jitter is caused by very small inconsistencies in the DAC clock edge timing between clock pulses?
Correct.

And a question if I may:
Are artefacts due to jitter caused by timing errors in the incoming digital signal i.e. the edges of the signal stream are not consistent?
It is caused both externally and internally. I showed examples of the external one in the video. Internal ones would be any source of interference in the circuits driving the clock DAC. With interfaces like USB that run asynchronously, most common source is internal.
 

EB1000

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Yet another video, this time on topic of jitter. It is a tough topic to cover and I had to do it over and simplify it from my first "take." Hopefully you can follow it. :)


Article: understanding digital audio measurements: https://www.audiosciencereview.com/...derstanding-digital-audio-measurements.10523/ SPL

Phonitor X Review (DAC & Headphone Amp): https://www.audiosciencereview.com/...pl-phonitor-x-review-dac-headphone-amp.21114/

Julian Dunn on Jitter:
https://www.aes.org/e-lib/browse.cfm?elib=6111
https://www.aes.org/e-lib/browse.cfm?elib=6772 Jitter Audibility: https://www.aes.org/e-lib/browse.cfm?elib=8354


With all due respect to AES published articles, this joke of a journal has an impact factor of 1.25, this is far below any predatory journal. I would take any claim made in their articles with a grain of salt...
 

Tks

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Getting ever so closer to making a video on filters :)
 
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