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Jitter and DSPs..?

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dsps jitter
13K views 74 replies 9 participants last post by  Ethan Winer 
#1 ·
Hi forum,


In my setup I've got a notoriously jitter-prone unit (a standard Sonos Connect) supplying signal via digital coax to my DSP (a miniDSP nanoDIGI), and then on via digital coax to my DAC.

My question is:
Which effect does the DSP have on the jitter coming from the Sonos unit?
- Does it just propagate the jitter?
- Does it worsen the jitter?
- Does it even remove the jitter? (perhaps due to the DSP being a state machine)

My reason for asking is that if the jitter proceeds to be a problem (regardless of the DSP being in the signal chain) I'd consider buying either a Sonos mod (Cullen/Volk/W4S/whatever) or a re-clocker to put between the Sonos and the DSP...

Any other thoughts in general regarding the issue?


B.R. Jon
 
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#2 ·
Is the jitter a problem? Does it need improvement?

It is hard to tell without a good AB comparison.

The DSP will reclock, probably an improvement. Whether or not it gives improvement, and how much, will depend on a lot of factors, including the design of the DSP, including whether it was bad in the first place.

Notoriously jitter prone? Is is a real audible problem or some nonsense you have been told or read, something to worry about? Just curious.
 
#4 ·
Is the jitter a problem? Does it need improvement?
It is hard to tell without a good AB comparison.
I cannot tell you that I know what the jitter from the Sonos (or any kind of jitter) sounds like.

The DSP will reclock, probably an improvement. Whether or not it gives improvement, and how much, will depend on a lot of factors, including the design of the DSP, including whether it was bad in the first place.
I have a Primare I22 amp with a built-in DAC module and it says in the specs that it reclocks the signal when using the USB-connection, but I'm using coax. Perhaps it does so too when using the coax, but it doesn't say explicitly anywhere.

Notoriously jitter prone? Is is a real audible problem or some nonsense you have been told or read, something to worry about? Just curious.
The latter. It's solely based on positive reviews of Sonos mods and reclockers, but perhaps they're all full of B and S? - It's definitely an option!
Another option is that the mods and separate reclockers have other positive effects than just removing jitter. Any thoughts?
 
#3 ·
Ditto those questions. I was thinking in the same direction and also wondering why the big concern.

I would NOT assume that inserting another clocking device in the path to be a solution. If I had doubts about the source I would make sure that the destination device handled the problem itself. As Wayne says, most DSP devices will establish their own clock. How they handle source errors likely depends on the nature of the error. Minor random errors will likely be corrected but larger scale biases might be a problem for any secondary clock system.
 
#12 ·
Thanks for taking time to respond to my ramblings! :)

Great advice with the REW testing - I'll definitely try that when I get home from work - but I have, though, read that sine waves shouldn't expose jitter in the same way as impulses do. I'll try messing around with some measurements and see if I can reproduce something interesting!

B.R.
 
#18 · (Edited)
First of all, thank you Ethan (I bet you've been discussing this about a million times before, so kudos for taking it up again!) and everyone else for chiming in.

I'm definitely more in the propellerhead camp than in the "audiophile true believer" camp (as would I think most people currently participating in this thread are), but I also recognize that even though measurements perhaps only show small differences between jitter-prone and low jitter equipment, there could(!) still be discernibles difference under certain circumstances - and I would think that it should be possible to sort out with double blinded testing, although I acknowledge that it might be hard to conduct correctly and to "everyone's" satisfaction.



Case: Many people claim that they can tell a difference between the standard Sonos Connect and (e.g.) a W4S-modded Sonos Connect. This is a real-life example (eliminating the need for a "jitter machine" or other artificial circumstances) where many users and reviewers claim OBVIOUS improvements.

1) Put together a panel consisting of some people with confirmation bias "for" the benefit of using low jitter devices, some people with bias against it and some neutral laymen, and let a facilitator run the test with a minimum of communication with the participants plus what-ever best practices else exist when doing this kind of testing.

2) Put together a setup with the two players in question connected to the same multiple-input DAC. Ensure that widely claimed "neutral/transparent" cables and equipment are used, of course. Ensure near-optimal room acoustics... wink, Ethan! :)

3) Perform listening tests that supposedly should be optimal for exposing jitter. Let the audiophiles decide! - It could be sine waves, impulses, instrument samples, music clips of various lengths, what-ever.



If the above experiment has already been conducted and its results are available, please forgive me AND SHOW THEM TO ME IMMEDIATELY, because God knows I'm tired of looking for them as well as surprised of their absence..!

What do you guys think?



EDIT: I know that the burden of proof (of showing that jitter in audio equipment can be heard and is perceptibly degrading to the sound) is always on the claimant, being the audiophiles, but I see clarification of the issue as being in the interest of both "camps", and as such it could just as well be "us" who take the initiative! - Also, it would lend more credence than just pointing to measurements showing very small effects of jitter, as this isn't the point of dispute - the audiobility is.
 
#19 ·
I don't know if your specific proposed test has ever been done, but there have absolutely been blind tests where people listened so the researchers could tell how much jitter you need before it's audible. Here's one that concluded the threshold is around 10 ns, which is 20 times more than is typical:

http://www.aes.org/e-lib/browse.cfm?elib=8354

Eric Benjamin and Benjamin Gannon, "Theoretical and Audible Effects of Jitter on Digital Audio Quality", Preprint 4826 of the 105th AES Convention, San Francisco, September 1998

From the conclusion:

"The effect of clock jitter in the digital interface was studied extensively. Measurements of the jitter spectrum of numerous digital audio sources, primarily DVD players, were conducted. A wide range of performance was found. The jitter spectrum of a typical source can be characterized as a white noise floor with one or many sinusoidal jitter components with a magnitude in the range of 10 ps to 10 ns rms. The effect of jitter induced in the interface was studied and found not to be a significant factor for short interconnection runs likely to found in a domestic environment. Several DACs and their DIRs were measured in order to characterize the sensitivity to distortion induced by jitter. These results were compared to each other and to results derived from simulations. Most DACs were found to be similar to each other and to the simulation in terms of susceptibility to jitter-induced distortion. That distortion is approximately -107+201og(F)+201og(J) dBr for sine wave signals at F kHz with J ns rms of clock jitter.

Up-Down threshold and AB comparison listening tests were conducted to determine the threshold of audibility for jitter-induced distortion. The threshold of audibility for pure tones was found to be about 10 ns rms at 20 kHz and higher at lower frequencies. For nearly all program material no audible degradation was heard for any amount of jitter added below the level at which the DIR lost lock. Certain program material was found in which an audible degradation due to jitter was heard. The threshold of audibility for these programs was generally found to be in the range of 30 ns rms to 300 ns rms for sinusoidal jitter. Finally, the audible degradation was found to correspond to measurable changes in the spectrum of the program material."
 
#20 · (Edited)
Thanks a lot for the excerpt of the study, which I guess pretty much dismisses that jitter can be "perceived" - which was clearly the aim of the study to clarify, but I still have some stuff that I would like to look into:

1) Am I right in assuming that the AB tests were made by comparing one DVD player versus another, and then seeing if the participants could point out the most jittery one of the two? - In this case, could the test results be skewed by other factors than just the measured amount of jitter that could make the participants prefer one over the other??

2) I've read claims that the effects of jitter manifest in the form of listening fatigue, and in this case I guess that "long term" testing should be made to expose this properly. Do you know of any studies that explore the claims about listening fatigue?
 
#22 ·
1) Am I right in assuming that the AB tests were made by comparing one DVD player versus another, and then seeing if the participants could point out the most jittery one of the two? - In this case, could the test results be skewed by other factors than just the measured amount of jitter that could make the participants prefer one over the other??
I honestly don't know, and I'm too lazy to read it all again. :|

2) I've read claims that the effects of jitter manifest in the form of listening fatigue, and in this case I guess that "long term" testing should be made to expose this properly. Do you know of any studies that explore the claims about listening fatigue?
I can tell you for certain that claims like that are always nonsense. Years ago some people claimed that digital music would give you a headache. I remember similar silliness in the 1960s about some types of rock 'n' roll. As FargateOne suggested, the only way to test such claims is with a blind test, and every time that's done the claims are disproved.

--Ethan
 
#23 ·
I've heard some pretty bad mp3's that gave me a headache in less than a few minutes. These were "supposed" to be high quality rips, so my expectations were as such.(not blind testing but I was tempered for a good sound). I've always assumed this to be from excessive compression. Cymbals sound like someone squishing a plastic bag, and the music was very flat overall. Watching/listening to music on Dish network could also be fatiguing, but mostly at elevated volume. At any volume you can put your ear next to a tweeter (during dish network) and it sounds like a swishorlyish kind of sound. Drives me nuts! Not sure if these observations are relevant but I thought I'd share.


Sent from my iPhone using Tapatalk
 
#24 ·
I've heard some pretty bad mp3's that gave me a headache in less than a few minutes. These were "supposed" to be high quality rips, so my expectations were as such.(not blind testing but I was tempered for a good sound). I've always assumed this to be from excessive compression. Cymbals sound like someone squishing a plastic bag, and the music was very flat overall. Watching/listening to music on Dish network could also be fatiguing, but mostly at elevated volume. At any volume you can put your ear next to a tweeter (during dish network) and it sounds like a swishorlyish kind of sound. Drives me nuts! Not sure if these observations are relevant but I thought I'd share.

Sent from my iPhone using Tapatalk
I have not heard of such effects giving headaches, but I do not doubt you a bit. They (lossy compression and noise) can sure mess with your noise floor.
 
#28 ·
Ethan, I agree. Volume compression doesn't bother me in the headache kind of way, but it is irritating when light cymbal work is just as loud as a singer belting away. This I've gotten used to. It's the crunchy low bit rate stuff that hurts. Lol. It does seem though, this has become less and less. I also understand why satellite providers have to go to the lengths they do. I'm sure one day it will not be so.


Sent from my iPhone using Tapatalk
 
#32 · (Edited)
Hi again guys,



My curiosity has led me to the point where I've actually bought a modded device in order to compare it directly to my out-of-the box Sonos Connect. The modded device is a 2009 Sonos ZP90 which has been modded by Dr. Gert Volk in 2010. The two players are hooked up to each their own little DAC (FiiO D03k Taishan) and then on to my amp (Primare I22).

The first tests I've done are some very simple tone test:

400 hz
https://www.dropbox.com/s/d5xacduvxfbndkx/400hz.m4a?dl=0

1.000 hz
https://www.dropbox.com/s/zxgvhth6z550r5k/1000hz.m4a?dl=0

4.000 hz
https://www.dropbox.com/s/hwo8v3r41123hwz/4000hz.m4a?dl=0

10.000 hz
https://www.dropbox.com/s/lrqufj9q6w3aadh/10000hz.m4a?dl=0

To my surprise, there actually is a discernible difference between the two players' outputs on the 1 khz and 10 khz sample.

I've double checked the results by switching around cables and using different inputs on the amp as well, but the results are the same. Risking to be lumbed in with the audiophile crowd, I think I'd discribe the first of the players (which is the standard Connect) to be a little "metallic", especially on the 1 khz sample.



I wonder why it's only possible to hear a difference on those two samples, while not on the 400 and 4.000 hz ones..?

Also, in general, what are your thought of the above sound bites?
 

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#33 ·
It's not clear what these files contain. I downloaded the 1 KHz version which has six sections. Is the first section one device, then the other device, then the first device again etc? If so, one reason they sound different is because the 2nd, 4th, and 6th sections are more than 1 dB louder than the other sections! If you want to learn how the "modded" version differs, here's what you need to do:

1) Record the output of the devices directly, not after playing through a loudspeaker!

2) Save the files as Wave (or AIFF on a Mac) and upload those for us to retrieve. MP4 type lossy compression is not suitable for analyzing subtle differences between audio files.

3) Describe clearly what is in the file(s) so we don't have to guess.

Then, even if one device is louder, I can account for that when assessing the difference between the devices.

--Ethan
 
#34 ·
Hi Ethan,

Thanks for the reply and sorry, you're of course right - I should've explained what's in the recordings:
The two players are joined within the Sonos controller to play the same file simultaneously. On each of the four recordings above it's then 3 second sound bites alternating between the two players - beginning with the standard device, then the modded, standard, modded, standard and finally the modded.

You're also right with regards to the volume, which is slightly higher on the modded version (as expected). However, I don't think that this accounts fully for the changed characteristics of the sound, especially on the 1 khz sound bite. If it's the sound of jitter, I cannot say, but it's definitely different.

When I'm getting to do the real analysis stuff, I'm of course going to record the outputs directly and in some lossless format. This was just a very crude initial comparison.

These are two other recordings of the same glorious quality: :wink2:
Standard - https://www.dropbox.com/s/px7cnwimnr6hywz/1khz-standard.m4a?dl=0
Modded - https://www.dropbox.com/s/9sfytpd18hajse3/1khz-modded.m4a?dl=0
Please feel free to adjust the volume in order to compare them properly! :smile:

B.R. Jon
 
#42 ·
I've finally made some measurements with the amp connected directly to my computer's soundcard - no mics involved.



It turns out that the difference I can hear when playing the 1khz test tone through my speakers doesn't appear when recording in this way. That "harshness" that I could hear on the non-modded Sonos Connect now also comes from the modded one, and what seems to be the deciding factor is the volume settings. Can't quite figure out why...

This link contains 4 four measurements from the standard Connect and 4 four from the modded Connect - at full volume, 90%, 80% and 70%:
https://www.dropbox.com/sh/twd8hostzbkw288/AAAfQnRiUgOMg9r1WTZ-Ii-ia?dl=0



1) Any thoughts on this phenomenon? - Is the described harshness at 90% and 100% volume a result of some sort of clipping? - Or is it actually meant to sound like that??

2) Also, are there any other differences between the output of the two players, when comparing?



Thanks,
Jon
 
#45 ·
Yes, the 90 and 100 files in both sets are severely clipped. This is easy to see just looking at the wave forms. I looked at an FFT but didn't add up all the harmonics. I'll estimate about 30 percent distortion.
Wow, kinda catastrophic that Sonos would sell a product that does that. Or is it just the digital input on my amp that's being a little wimp?
I guess I'll just have to turn down the volume with the Sonos controller - I've always had it on fixed volume (100%) and then adjusted volume on my amp, but I guess that isn't a very good idea then!

That would sound a little harsh.
Not to mention potentially devastating for the speakers, right?
Also, as I've written futher back in this thread, I've experienced some harsh S sounds from the vocals when playing loud. I guess this could be the explanation for that..?
 
#47 ·
Yeah, I've searched the issue myself for a while, and other people complain over clipping from the Sonos Connect. I guess maybe it has to do with how sensitive the digital input is on one's DAC.

Just what is your setup?
My setup is:
Sonos Connect --> digital coax cable --> DAC --> 2x phono --> amplifier --> speakers

BTW, I've tried with two different DACs - FiiO D03k Taishan and the one built into my amp (Primare I22) - which yields the same results with regards to the clipping issue.
 
#50 ·
Between the Sonos Connect and the DAC I have a DSP, and it appears that if I use that to define a gain of -10 dB to the signal, then no clipping occur and the 1 kHz tone is nice and pretty - both when listening and when looking (at the waveform in Audacity).
I guess this tells us that the signal leaving the Connect isn't "clipped", as such - otherwise I wouldn't be able to recover the correct signal, am I right? - It must have something to do with the DAC just not being able to interpret the signal correctly per default, for some reason. Notice, that I've tried with two different DAC models, with the same results.
 
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