Let's talk jitter.

[Ittaku]

Well then what we can all agree on and conclude is that we need more research...

[Grant Slack]

.... if we want to justify very expensive gear on the basis of how low and how tailored is its jitter.

[Ittaku]

13 minutes ago, Grant Slack said:

.... if we want to justify very expensive gear on the basis of how low and how tailored is its jitter.

That line of thinking will get you nowhere with audiophilia. Surely faith is more important than science and research...

[Guest scumbag]

On 31/10/2018 at 7:47 PM, rmpfyf said:

 

Nope. Jitter is not noise. The method of measurement doesn't reflect the phenomenon we seek to evaluate. Think 'bout it - something happens slightly later or earlier than ideal, over and over, in a random way. 

 

That's a timing artefact - we don't measure time in dB.

We do measure jitter in dB. https://www.audiosciencereview.com/forum/index.php?threads/jitter-seconds-to-db.2014/

What you are saying in effect is that a phenomenon that changes the ouput of a device has no effect on the output of a device. Jitter changes the sound. It may do it in a time related / random way but it is affecting the output. Therefore it's affects can be measured in dB

[Guest scumbag]

1 hour ago, Grant Slack said:

.... if we want to justify very expensive gear on the basis of how low and how tailored is its jitter.

I don't remember reading a single post by a person on this forum trying jusify their purchase of a dac based on its jitter figures. Can you sight me a link? Or are you just surmising other people's motives? 

[sir sanders zingmore]

20 minutes ago, scumbag said:

I don't remember reading a single post by a person on this forum trying jusify their purchase of a dac based on its jitter figures. 

That’s because 

On 31/10/2018 at 5:01 PM, Sir Sanders Zingmore said:

Jitter is no longer a problem in modern, well designed DACs. Even sensibly priced ones. 

 

“Jitter” is often  used (along with “digital hash”) as a meaningless word to explain perceived differences between DACs and to sell us stuff we don’t need. 

 

(Flame suit at the ready)

 

[Ittaku]

On 31/10/2018 at 5:01 PM, Sir Sanders Zingmore said:

Jitter is no longer a problem in modern, well designed DACs. Even sensibly priced ones.

Getting back to your original quote since you quoted yourself... that's a distinct possibility, but it is audible at some threshold. What I'm trying to determine is where? Microseconds? Nanoseconds? Picoseconds? Femtoseconds? It's definitely audible in the microsecond range, but assuming it's nanoseconds, how many? If I ever find time I'll try and massage some data to see if I can create some samples.

[Guest scumbag]

This might add something to the discussion. 

 

 

[MLXXX]

13 minutes ago, Ittaku said:

Getting back to your original quote since you quoted yourself... that's a distinct possibility, but it is audible at some threshold. What I'm trying to determine is where? Microseconds? Nanoseconds? Picoseconds? Femtoseconds? It's definitely audible in the microsecond range, but assuming it's nanoseconds, how many? If I ever find time I'll try and massage some data to see if I can create some samples.

There is the question of the frequency distribution of the jitter, e.g. is it low frequency periodic jitter from mains hum, medium frequency quasi-periodic jitter from phase locked loop overshoots, or is mostly very rapid jitter at extremely high frequencies causing momentary slight changes in the phase of the clock frequency?

 

There is also the question of the probability distribution of the jitter amplitude,   e.g. a gaussian normal curve, or concentrated very much at particular amplitudes. 

Edited November 13, 2018 by MLXXX

[LHC]

9 minutes ago, Ittaku said:

Getting back to your original quote since you quoted yourself... that's a distinct possibility, but it is audible at some threshold. What I'm trying to determine is where? Microseconds? Nanoseconds? Picoseconds? Femtoseconds? It's definitely audible in the microsecond range, but assuming it's nanoseconds, how many? If I ever find time I'll try and massage some data to see if I can create some samples.

Agree. That was the OP question. Once again I plead for someone to post citations of recent published science research work (not faith) on the audibility threshold. 

[Guest Simonon]

All of the jitter measurements of oscillators that I have ever measured are in the order of 10 to 50 pico seconds with phase noise not even worth a mention. These measurements being with a calibrated 1ghz R&S cro and spectrum analyzer. I am currently mucking about with an iq audio dac plus costing $50 on a Raspberry pi model 3 running Volumio. I have to say it sounds stunning playing back a flac, even on headphones via the inbuilt head phone amp. All for $150 dollars including the Raspberry pi plus case and power supply. Modern electronics has come along way with a lot of hardware packed in a tiny chip. With a limited number of chip sets available I do not understand why some dacs cost upwards of 5 grand given the performance of this Raspberry Pi and IQ audio dac.
The crazy plan basically for something to do and a challenge is to replace the completely stuffed reel to reel section of an akai tube M8 with a Raspberry pi and touch screen ( making it look like a steam punk reel to reel and cool). The IQ audio dac will run into the lovely 6w single ended tube amps. I rigged it up on the work bench into my high efficiency Wharfedales to check if this is worth the effort and it sounds very nice even without rebuilding the amps. Tidal Hifi streaming is impressive at this early stage.
So given performance of this little IQ audio thingy is jitter even worth considering.

[LHC]

10 minutes ago, MLXXX said:

There is also the question of the probability distribution of the jitter amplitude,   e.g. a gaussian normal curve, or concentrated very much at particular amplitudes. 

By 'amplitude', did you mean the error in time? Or the amplitude when one does the spectrum analysis?

[MLXXX]

4 minutes ago, LHC said:

By 'amplitude', did you mean the error in time? Or the amplitude when one does the spectrum analysis?

I meant the instantaneous error in time of one sample compared with keeping strictly to the current average clockrate. 

(My surmise is that jitter levels are typically so low that it would become academic to examine the speed and depth of the jitter components.)

[LHC]

1 hour ago, scumbag said:

I don't remember reading a single post by a person on this forum trying jusify their purchase of a dac based on its jitter figures. Can you sight me a link? Or are you just surmising other people's motives? 

This doesn't quite answer your question. But when someone has an extremely well sorted digital front end, within a highly resolving system, then jitter can become important. I think that was the context for @rmpfyf when he talked about clock rolling. 

[Guest rmpfyf]

2 hours ago, scumbag said:

We do measure jitter in dB. https://www.audiosciencereview.com/forum/index.php?threads/jitter-seconds-to-db.2014/

What you are saying in effect is that a phenomenon that changes the ouput of a device has no effect on the output of a device. Jitter changes the sound. It may do it in a time related / random way but it is affecting the output. Therefore it's affects can be measured in dB

dB purely as a measure of the amplitude of a phenomena - not noise.

 

3 hours ago, Grant Slack said:

.... if we want to justify very expensive gear on the basis of how low and how tailored is its jitter.

Doesn't need to be particularly expensive, IMHO.

 

2 hours ago, Ittaku said:

Getting back to your original quote since you quoted yourself... that's a distinct possibility, but it is audible at some threshold. What I'm trying to determine is where? Microseconds? Nanoseconds? Picoseconds? Femtoseconds? It's definitely audible in the microsecond range, but assuming it's nanoseconds, how many? If I ever find time I'll try and massage some data to see if I can create some samples.

Still think that's not a correct way to look at things, given it's a statistical distribution of timing inaccuracy that we're trying to characterise the audible effects of - though still, more research required. 

 

1 hour ago, Simonon said:

All of the jitter measurements of oscillators that I have ever measured are in the order of 10 to 50 pico seconds with phase noise not even worth a mention

The first part doesn't sufficiently characterise jitter, the latter needs unpacking - what does 'not even worth a mention' mean?

 

1 hour ago, Simonon said:

So given performance of this little IQ audio thingy is jitter even worth considering.

That's subjective, though as ever if you're happy with what you've got and that part of the journey is solved for you - that's a good outcome. 

 

Still tweaking here though.

[Grant Slack]

3 hours ago, scumbag said:

I don't remember reading a single post by a person on this forum trying jusify their purchase of a dac based on its jitter figures. Can you sight me a link? Or are you just surmising other people's motives? 

Hello scumbag, 

 

well, my tongue-in cheek comment was actually referring to the OP -- which, I assume, you have read.

 

I wasn't referring to the OP's personal decisions, but he was alluding to the high-end industry making a fuss about super-low jitter numbers as a reason to choose their DAC. And, presumably, buyers of those DACs believe what the manufacturers say about its importance.

 

Apologies if I got that all completely wrong.

 

Regards,
Grant

[Guest Simonon]

The first part doesn't sufficiently characterise jitter, the latter needs unpacking - what does 'not even worth a mention' mean?

My bad with the terminology in regards to phase noise. One of the measurements I performed regulary was phase noise and jitter measurements of the local oscillator on digital broadcast transmitters using some very nice high end test gear. Phase noise actually became problematic when a precision 7v power supply became noisey in the local oscillator synthesiser module of a particular high power digital television transmitter causing a phenomenom called centre carrier breakthrough which ultimately affected the MER or modulation error ratio at the output of the transmitter. We had a separate program on the spectrum analyser to measure the phase noise of the local oscillator.

I started using this equipment to measure DA converter clock jitter and phase noise of a bunch of dacs and cd players I have out of interest and fun.

I found phase noise of the DA converter clock to be so low it was negligable being so far down in the spectrum analyzers noise floor it was hard to gain a meaningful measurement and in my opinion to not be a factor that would audibly affect sound. Likewise even on a basic clock in an entry level cd player measured jitter was in the order of pico seconds.

I agree that I may be missing something here or their were flaws in my methodology as my background is in digital broadcast and Rf which is why I find this thread interesting. I always like to be proven wrong but not without a robust argument[emoji3]

I would like to experiment more with digital music servers, DA converter chips and clocks but find the cost hard to justify for an experiment when the performance of modern equipment is so good.

Great thread.

 

 

 

[Ittaku]

39 minutes ago, rmpfyf said:

Still think that's not a correct way to look at things, given it's a statistical distribution of timing inaccuracy that we're trying to characterise the audible effects of - though still, more research required.

I understand. But at the very least, a stochastic random jitter with normal distribution around a mean is what I had in mind as a starting point. Then other types of jitter could be explored.

 

3 minutes ago, Grant Slack said:

well, my tongue-in cheek comment was actually referring to the OP -- which, I assume, you have read.

I was the opening poster. I don't really mind what direction this thread takes, so long as it's about jitter.

[LHC]

3 minutes ago, Simonon said:

Likewise even on a basic clock in an entry level cd player measured jitter was in the order of pico seconds.

In the video posted above by @scumbag the guy claims he could hear jitter at 0.2 ps. That is an order of magnitude lower than your measurement. 

[Ittaku]

13 minutes ago, LHC said:

In the video posted above by @scumbag the guy claims he could hear jitter at 0.2 ps. That is an order of magnitude lower than your measurement. 

Claims, yes, but he didn't actually describe what he heard or what his methodology was but people can claim all sorts of things...  Anyway if his unsubtantiated comment can be trusted, then that puts us into the femtosecond range.

[Guest Simonon]

So here is a question that somebody may be able to answer
Why is their a revival of interest in the perceived analogue sound of TDA 1540 equipped early generation 14 bit CD players and later 16 bit TDA1541 dac chips.
I note one popular methodology is to use a number of dac chips in parrallel to average the slight variation in timing of these chips again for a perceived more rounded analogue sound or so the marketing says.
Would the ability to vary clock jitter have a similar affect to suit personal tastes? Would a jitter free clock sound harsh and sibilant when compared to the same dac chip with a relatively high amount of clock jitter. I am trying to gain an understanding of how jitter will audibly affect sound when compared to the use of dither in digital mastering for example.

[Guest Simonon]

Claims, yes, but he didn't actually describe what he heard or what his methodology was but people can claim all sorts of things...  Anyway if his unsubtantiated comment can be trusted, then that puts us into the femtosecond range.

I wonder if he is also into power cords and bybees. I take these claims with a grain of salt. Maybe he also writes equipment reviews.

[Ittaku]

5 minutes ago, Simonon said:

Would the ability to vary clock jitter have a similar affect to suit personal tastes? Would a jitter free clock sound harsh and sibilant when compared to the same dac chip with a relatively high amount of clock jitter. I am trying to gain an understanding of how jitter will audibly affect sound when compared to the use of dither in digital mastering for example.

It's been my impression in the past when DACs had far more jitter, that it introduced the hard brittle sound that early digital was renowned for. When those older DACs had reclocking done on their input side a lot of that went away without actually changing the DAC. I don't know how to categorise the actual type of jitter they had but the magnitude was thousands of times higher than modern DACs have. Modern DACs jitter is said to subtly affect it differently - I've heard people say that the image is flatter and there is less depth and volume to instrument portrayal but I haven't done experiments at modern dac jitter levels myself to confirm this.

[Ittaku]

2 minutes ago, Simonon said:

18 minutes ago, Ittaku said:

Claims, yes, but he didn't actually describe what he heard or what his methodology was but people can claim all sorts of things...  Anyway if his unsubtantiated comment can be trusted, then that puts us into the femtosecond range.

I wonder if he is also into power cords and bybees. I take these claims with a grain of salt. Maybe he also writes equipment reviews.

Heh well I'd like to know a reviewer's stance on some of these things... then I can decide how much weight to put to their opinions on everything else.

Edited November 13, 2018 by Ittaku

[Guest scumbag]

1 hour ago, rmpfyf said:

dB purely as a measure of the amplitude of a phenomena - not noise.

 

Doesn't need to be particularly expensive, IMHO.

 

Still think that's not a correct way to look at things, given it's a statistical distribution of timing inaccuracy that we're trying to characterise the audible effects of - though still, more research required. 

 

The first part doesn't sufficiently characterise jitter, the latter needs unpacking - what does 'not even worth a mention' mean?

 

That's subjective, though as ever if you're happy with what you've got and that part of the journey is solved for you - that's a good outcome. 

 

Still tweaking here though.

Bear with me here. Say you have a dac with very high jitter. So much that it if easily audible. It is a distortion as at any point in time it represents a deviation from the original signal. Which is measured in dB. 

https://www.stereophile.com/reference/1093jitter/index.html ". Specifically, jitter with a frequency of 1kHz affecting a DAC reproducing a 7kHz sinewave will create spurious output tones at 6kHz and 8kHz. If the jitter has a frequency of 2kHz, the jitter-created artifacts will appear at 5kHz and 9kHz. These sidebands around the signal being decoded aren't harmonically related to the signal, making them particularly unpleasant. When the DAC is reproducing music (which has a constantly changing spectral content) and is controlled by a jittered clock (that may be jittered at several frequencies), the potential for generating a highly complex spectrum of jitter-induced spuriae is obvious. If the jitter is "white" (having a random spectral distribution rather than discrete frequency components), analog white noise will be added to the DAC's output signal"