Jitter Correlation to Audibility

[stv014]

Quote:

Originally Posted by robertsong /img/forum/go_quote.gif
 
[size=x-small][2] 20psec P-P of data-correlated jitter audibility threshold at certain frequencies and "A simple model of jitter error audibility has shown that white jitter noise of up to 180psec P-P can be tolerated in a DAC, but that even lower levels of sinusoidal jitter may be audible"[/size]

 
It may be nitpicking, as the number is not realistic for a signal that resembles actual music anyway (most people do not listen to pure 22 kHz tones at 110 dB SPL in a perfectly silent anechoic chamber, and even then the jitter frequency has to be chosen such that a sideband appears at the frequency where human hearing is the most sensitive), but it is 20 ps peak (see the quote above by anetode), not P-P. That is, 40 ps p-p, which is also consistent with the ~-117 dB sideband level (see formula in the previous post).

 

[bigshot]

You guys have no idea how your comments are being read by people without the technical background you have. You might think that they're impressed, but the truth is, they are just confused and end up ignoring what you say and assuming what they already think is true is fact. When you allow for the possibility, however unlikely that there is a possibility that jitter is a problem, you just muddy the waters more. Perhaps it's good science, but it's lousy advice for people who just want to listen to music.

Go look at Robersong's comment to MikeAJ. Robertsong read MikeAJ's equivocating and thoroughness as saying the exact opposite of what he was actually saying. Then MikeAJ came back with a comment that had even more confusing t crossing and i dotting.

This is the problem with discussions of jitter. It isn't about theoretical sound. It's about real world noise. All that matters is, can it be heard in music at comfortable listening levels? The answer to that is clear, and no amount of technical back and forth is going to change that. We'll just end up at the same conclusion with even more regular people confused.

I understand exactly what you guys are trying to say. The problem is, you have to consider your audience. It isn't being read the way you are intending it to be read at all. Sometimes Sound Science is as good as snake oil salesmen at confusing things.

 

[limpidglitch]

Pah. They need some fiber in their diets.
Keep up the good work, stv'n all.

 

[Theta Alpha 1]

Quote:

 
It may be nitpicking, as the number is not realistic for a signal that resembles actual music anyway (most people do not listen to pure 22 kHz tones at 110 dB SPL in a perfectly silent anechoic chamber, and even then the jitter frequency has to be chosen such that a sideband appears at the frequency where human hearing is the most sensitive)

 
Quote:

You guys have no idea how your comments are being read by people without the technical background you have. You might think that they're impressed, but the truth is, they are just confused and end up ignoring what you say and assuming what they already think is true is fact.

 
I think Amir M has a deep technical background and is not confused in the slightest.
 
Why should an average consumer be "impressed" when there is a divide amongst the technically gifted and EE's?
 
For example, stv014 says above most people don't listen to music at 110dB SPL in anechoic chambers, however Amir says 2.5ns jitter is audible on laptop speakers.  http://www.whatsbestforum.com/showthread.php?3808-The-sound-of-Jitter
 
So, you may as well pay a little extra for the equipment without jitter and feel safe.  Like ripping to lossless to feel safe even if there is no reason to versus 320kbps

 

[stv014]

Quote:

Originally Posted by Theta Alpha 1 /img/forum/go_quote.gif
 
For example, stv014 says above most people don't listen to music at 110dB SPL in anechoic chambers, however Amir says 2.5ns jitter is audible on laptop speakers.  http://www.whatsbestforum.com/showthread.php?3808-The-sound-of-Jitter

 
It is just another contrived and unrealistic sample that uses a loud ultrasonic tone modulated by a jitter frequency that is deliberately chosen such that jitter products appear in the peak sensitivity range of human hearing (~3 kHz). It would be very unusual for real music to have a spectrum like that. Of course, a 3 kHz tone, even at a relatively low level, is audible when there is nothing else audible to mask it. Although it is not what is making the effect audible, but the jitter simulation used there is not of particularly high quality either, and also produces aliasing.
 
By the way, it is in fact not 2.5 ns, but 25 ns jitter, as the sidebands are 60 dB down from the input signal.
 
If anyone is interested in ABX testing jitter with audio that is not made for bats, post a short (<= 30 s) sample of music you think would be best suited for the testing (note that jitter is most audible on high frequency pure tones), and a description of the jitter to be simulated (amount, spectral characteristics, etc., or the JTest of an existing device to be used as a reference). See also this post for more information.

 

[nick_charles]

Quote:

 
It is just another contrived and unrealistic sample that uses a loud ultrasonic tone modulated by a jitter frequency that is deliberately chosen such that jitter products appear in the peak sensitivity range of human hearing (~3 kHz). It would be very unusual for real music to have a spectrum like that. Of course, a 3 kHz tone, even at a relatively low level, is audible when there is nothing else audible to mask it. Although it is not what is making the effect audible, but the jitter simulation used there is not of particularly high quality either, and also produces aliasing.
 
By the way, it is in fact not 2.5 ns, but 25 ns jitter, as the sidebands are 60 dB down from the input signal.
 
If anyone is interested in ABX testing jitter with audio that is not made for bats, post a short (<= 30 s) sample of music you think would be best suited for the testing (note that jitter is most audible on high frequency pure tones), and a description of the jitter to be simulated (amount, spectral characteristics, etc., or the JTest of an existing device to be used as a reference). See also this post for more information.

 
I don't have a suitable sample to hand but  for a model of bad jitter that is easy 
 
http://www.stereophile.com/content/mcintosh-ms750-music-server-measurements
 
the poster child for bad measured jitter

 

[robertsong]

Hi. Just in case people think I disappeared,  I'm still here and I've read through most of the discussion. Lots of different things going through my mind right now. Unfortunately this is not a good time for me to tie my brain in a knot. Hopefully this week.

 
 
 
Quote:

If anyone is interested in ABX testing jitter with audio that is not made for bats, post a short (<= 30 s) sample of music you think would be best suited for the testing (note that jitter is most audible on high frequency pure tones), and a description of the jitter to be simulated (amount, spectral characteristics, etc., or the JTest of an existing device to be used as a reference). See also this post for more information.

 
 
Yes. I'm very interested as long it is a EAC ripped .wav track (16bit 44.1khz). I'll gladly send you a track if you know of a way for me transfer it to you (probably around 50mb).

 

[limpidglitch]

Quote:

I'll gladly send you a track if you know of a way for me transfer it to you (probably around 50mb).

 
Take your pick.

 

[nick_charles]

Quote:

 
Yes. I'm very interested as long it is a EAC ripped .wav track (16bit 44.1khz). I'll gladly send you a track if you know of a way for me transfer it to you (probably around 50mb).

 
 
We are a high profile forum and do not need the RIAA/SONY etc getting pissy with us - the < 30s clause allows us to use "fair use" provisions ,  posting entire tracks here is a no-no as it can bring down the weight of the absurd DMCA on us 

 - we are also not allowed to discuss file sharing by the TOS of the forum

 

[stv014]

Quote:

 
I don't have a suitable sample to hand but  for a model of bad jitter that is easy 
 
http://www.stereophile.com/content/mcintosh-ms750-music-server-measurements
 
the poster child for bad measured jitter

 
Simulated version:
 

10 pairs of sidebands are included. The noise component is probably not accurate, especially since the FFT size used by Stereophile is not known. The jitter level is ~70-80 ns (peak to peak), most of which is low frequency noise. So, it should be bad enough.

 

[leogodoy]

So what now? Accusing manufacturers of using "unscientfic tweaks and magic" on products design can get you banned.

 

[BlindInOneEar]

All this fussing over whether jitter might be causing a problem instead of just enjoying your music!   It's kind of like being so worried that there might be a monster under the bed that you end up forgetting all about that rather attractive person in bed with you. 
 

 

[bigshot]

So, you may as well pay a little extra for the equipment without jitter and feel safe.

That is the main upsell technique used by high end audio salesmen. They throw up a lot of confilicting information, then they point to the absolute quack worse case scenario and say, "Maybe you can't hear it, but don't you want to be SURE."

It's easy to answer. "I want to know for sure so I'm not throwing money at something I'll never be able to hear." I expect an audible improvement when I upgrade, not just better numbers on a sheet of paper.

 

[Steve Eddy]

Quote:

All this fussing over whether jitter might be causing a problem instead of just enjoying your music! 
 

 
I've never been able to figure out how someone can listen so critically as to discern the finest little differences and enjoy listening to the music at the same time. For me the enjoyment of reproduced music is all about the gestalt. And if I'm focusing narrowly on some niggling little detail, I lose the gestalt. It's like trying to enjoy making love to a woman while at the same time being intensely focused on some mole she has on her neck.
 
se

 

[bigshot]

One of the first things I learned in sound mixing was that it isn't about details... It's about overall balances. If you get the overall right, the details will take care of themselves.