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Is jitter audible and what does it sound like?

Reply #75
Could you explain this in a little more detail?  I'm not understanding why HDMI would influence jitter of the downstream system.  HDMI is a packet-based digital protocol, how does the rate at which packets arrive influence the analog performance of the device?


The rate at which the packets arrive is not the only relevant variable.

For example SP/DIF packets arrive in a fairly continuous stream while HDMI packets generally arrive with big time delays between them.

Audio is a fairly small percentage of a HDMI stream and the packets are relatively sparse.

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Unless the DAC is actually clocked off of the HDMI clock (which would be tough since a lot of different HDMI clocks are possible), the DAC's jitter shouldn't depend on if you fed it with HDMI or any other input.  Just like how playing Spotify vs. iTunes doesn't change the jitter in your sound card.


You're right - the jitter that was observed with some AVRs and HDMI inputs should not have happened.  It is probably a classic case of the squeaky gear.  I seem to recall comparing Miller's jitter numbers to  the standards in:

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

and Miller's data was too incomplete for a comparison.

I'm under the impression that by the time your audio card sees the audio data stream from these services, it has been cleaned up quite a bit.

Most DAC chips are fairly susceptible to jitter all by themselves, but the buffering that drives them (such as in CD players) has generally been pretty good.

Is jitter audible and what does it sound like?

Reply #76
Could you explain this in a little more detail?  I'm not understanding why HDMI would influence jitter of the downstream system.  HDMI is a packet-based digital protocol, how does the rate at which packets arrive influence the analog performance of the device?


The rate at which the packets arrive is not the only relevant variable.

For example SP/DIF packets arrive in a fairly continuous stream while HDMI packets generally arrive with big time delays between them.

Audio is a fairly small percentage of a HDMI stream and the packets are relatively sparse.


But it shouldn't be relevant at all.  It should not matter how sparse the audio packets are or aren't, or how the stream works.  Jitter is just about how well an analog waveform representing an ideal sampling clock approximates that ideal clock.  The data that is ultimately encoded onto that clock doesn't change anything, which is why the HDMI point is so strange.  Something else must be going on.

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Unless the DAC is actually clocked off of the HDMI clock (which would be tough since a lot of different HDMI clocks are possible), the DAC's jitter shouldn't depend on if you fed it with HDMI or any other input.  Just like how playing Spotify vs. iTunes doesn't change the jitter in your sound card.


You're right - the jitter that was observed with some AVRs and HDMI inputs should not have happened.  It is probably a classic case of the squeaky gear.  I seem to recall comparing Miller's jitter numbers to  the standards in:

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

and Miller's data was too incomplete for a comparison.

I'm under the impression that by the time your audio card sees the audio data stream from these services, it has been cleaned up quite a bit.

Most DAC chips are fairly susceptible to jitter all by themselves, but the buffering that drives them (such as in CD players) has generally been pretty good.


Yeah something more is happening. You have to get HDMI data to a DAC at a rate that matches the DAC's clock on average.  There are two different ways you could do that, use your own clock which you speed up and slow down slightly so that its average sampling rate matches the HDMI's packet rate or run the DAC async from the rest of the receiver off of a clock you derive from the HDMI.  If you do the former, the pitch wobbles some tiny, tiny amount at a small fraction of a Hz but you don't care about the HDMI clock.  I doubt this is done much, and the wobble is probably much too low frequency to be detected.  If you do the latter, the obvious way to do this would be to take the HDMI clock and feed it into a PLL which would generate the clock you wanted while stabilizing it, making the HDMI clock irrelevant as well. 

If this problem really only happened over HDMI (as opposed to merely having a broken DAC), I'd guess they did something crazy like try to divide down the ~160 MHz HDMI clock to 48k without a PLL.  That would certainly give you some jitter.  It would probably also give you a pitch error since I doubt the HDMI clock is always an integer multiple of 48,000 . . .

Is jitter audible and what does it sound like?

Reply #77
Yeah something more is happening. You have to get HDMI data to a DAC at a rate that matches the DAC's clock on average.  There are two different ways you could do that, use your own clock which you speed up and slow down slightly so that its average sampling rate matches the HDMI's packet rate or run the DAC async from the rest of the receiver off of a clock you derive from the HDMI.  If you do the former, the pitch wobbles some tiny, tiny amount at a small fraction of a Hz but you don't care about the HDMI clock.  I doubt this is done much, and the wobble is probably much too low frequency to be detected.  If you do the latter, the obvious way to do this would be to take the HDMI clock and feed it into a PLL which would generate the clock you wanted while stabilizing it, making the HDMI clock irrelevant as well. 

If this problem really only happened over HDMI (as opposed to merely having a broken DAC), I'd guess they did something crazy like try to divide down the ~160 MHz HDMI clock to 48k without a PLL.  That would certainly give you some jitter.  It would probably also give you a pitch error since I doubt the HDMI clock is always an integer multiple of 48,000 . . .

The HDMI spec contains a chapter that describes the clock regeneration in a receiver. While an implementation may choose any method it sees fit, the overall process is pretty clear and straightforward. However, there are two modes, depending on whether the video and audio clocks are coherent or not. You can't meaningfully discuss the situation when you don't know which mode is active. Furthermore, the signal source has a lot of influence on the process because it determines the mode and supplies the division/multiplication factors to the receiving device. It makes it harder to determine the guilty party when the result turns out to be wanting.

There is no need for the resulting clock to be jittery. If both sender and receiver are working well, the resulting clock can be just fine. People seem to extrapolate the problems some devices have to the HDMI interface in general.

Is jitter audible and what does it sound like?

Reply #78
People seem to extrapolate the problems some devices have to the HDMI interface in general.

Are there any recorded samples that are readily available which can be used to demonstrate an audible problem with poorly designed devices?
Is 24-bit/192kHz good enough for your lo-fi vinyl, or do you need 32/384?

Is jitter audible and what does it sound like?

Reply #79
Are there any recorded samples that are readily available which can be used to demonstrate an audible problem with poorly designed devices?

I didn't want to imply they are audible. Some people seem to have measured poor jitter performance with some HDMI setups. I can't say how serious they are in practice. I'm also sceptical regarding the ability of some people to troubleshoot their measurements.

It would be necessary to have a proper investigation into the source of the poor jitter measurements some have quoted, in order to find out what went wrong. It might have been poor design of the unit under test, but that is not the only possible explanation.

Is jitter audible and what does it sound like?

Reply #80
I didn't want to imply they are audible.

I'm sorry to imply that I thought you did.  I guess I honed in on the word problem and wondered if it was more than just not in keeping with good engineering practice.
Is 24-bit/192kHz good enough for your lo-fi vinyl, or do you need 32/384?

Is jitter audible and what does it sound like?

Reply #81
Yeah something more is happening. You have to get HDMI data to a DAC at a rate that matches the DAC's clock on average.  There are two different ways you could do that, use your own clock which you speed up and slow down slightly so that its average sampling rate matches the HDMI's packet rate or run the DAC async from the rest of the receiver off of a clock you derive from the HDMI.  If you do the former, the pitch wobbles some tiny, tiny amount at a small fraction of a Hz but you don't care about the HDMI clock.  I doubt this is done much, and the wobble is probably much too low frequency to be detected.  If you do the latter, the obvious way to do this would be to take the HDMI clock and feed it into a PLL which would generate the clock you wanted while stabilizing it, making the HDMI clock irrelevant as well. 

If this problem really only happened over HDMI (as opposed to merely having a broken DAC), I'd guess they did something crazy like try to divide down the ~160 MHz HDMI clock to 48k without a PLL.  That would certainly give you some jitter.  It would probably also give you a pitch error since I doubt the HDMI clock is always an integer multiple of 48,000 . . .

The HDMI spec contains a chapter that describes the clock regeneration in a receiver. While an implementation may choose any method it sees fit, the overall process is pretty clear and straightforward. However, there are two modes, depending on whether the video and audio clocks are coherent or not.


Ha, looking at the spec, the two recommended ways of dealing with this problem are exactly the two solutions I described above.  Not a bad guess.  But it also suggests that the HDMI data clock and audio clock may be set to be integer multiples, so I suppose those jittery devices did not use a PLL and instead simply divided down the data clock.  Not great design.

Is jitter audible and what does it sound like?

Reply #82
Yeah something more is happening. You have to get HDMI data to a DAC at a rate that matches the DAC's clock on average.  There are two different ways you could do that, use your own clock which you speed up and slow down slightly so that its average sampling rate matches the HDMI's packet rate or run the DAC async from the rest of the receiver off of a clock you derive from the HDMI.  If you do the former, the pitch wobbles some tiny, tiny amount at a small fraction of a Hz but you don't care about the HDMI clock.  I doubt this is done much, and the wobble is probably much too low frequency to be detected.  If you do the latter, the obvious way to do this would be to take the HDMI clock and feed it into a PLL which would generate the clock you wanted while stabilizing it, making the HDMI clock irrelevant as well. 

If this problem really only happened over HDMI (as opposed to merely having a broken DAC), I'd guess they did something crazy like try to divide down the ~160 MHz HDMI clock to 48k without a PLL.  That would certainly give you some jitter.  It would probably also give you a pitch error since I doubt the HDMI clock is always an integer multiple of 48,000 . . .

The HDMI spec contains a chapter that describes the clock regeneration in a receiver. While an implementation may choose any method it sees fit, the overall process is pretty clear and straightforward. However, there are two modes, depending on whether the video and audio clocks are coherent or not. You can't meaningfully discuss the situation when you don't know which mode is active. Furthermore, the signal source has a lot of influence on the process because it determines the mode and supplies the division/multiplication factors to the receiving device. It makes it harder to determine the guilty party when the result turns out to be wanting.

There is no need for the resulting clock to be jittery. If both sender and receiver are working well, the resulting clock can be just fine. People seem to extrapolate the problems some devices have to the HDMI interface in general.



Agreed that there is no need for the resulting clock to be jittery.  One of the hallmarks of digital data transmission that as long as the error rates are not too high, the digital data can be recovered as accurately as desired at the receiving end.  It is just a matter of properly processing the data properly before transmission, and again after reception. If you have to add parity or CRCs or whatever, so what? If you have to reconstruct, buffer, reclock, whatever, so what?  Digital processing and data transmission are cheap and getting cheaper.  If it is not practical this week, wait a while.

There are no generally accepted  standards (that I know of) for what constitutes audible jitter. Of course there are no standards  (that I know of) for what constitutes audible THD, IM, or FR and phase differences either.  Therefore whenever someone says there is too much jitter (or THD, IM, FR or phase changes), it would appear to lack general meaning.  That leaves the door open for people to say whatever they will, for whatever reason or no reason.



Re: Is jitter audible and what does it sound like?

Reply #83
I hope I put this in the right forum. You've probably been asked this a million times, but I trawled the web (mostly searching "dan lavry" + "jitter", as I figured he was the "master") as well as his forum, and I couldn't really find my answer, so I asked on his forum (which gave this response: http://www.lavryengineering.com/lavry_foru...f=1&t=7449), and I'll also ask here to hear your opinion:

If we're talking home audio listening (not recording), is jitter then audible, and how does it sound? I'm only talking about playing CDs and digital audio files from either a CD player, or your computer or a streamer through a dac into your amplifier.
Let's also for the time being assume that the analogue to digital conversion during recording/mastering was done well to begin with, and let's assume that the converter you use is of fairly good quality.

I discussed this with an audiophile friend. My own impression is that with 16 bit audio, jitter starts to become audible at -96 dB (without dithering), so with music recorded at sensible levels, it will not be audible, as all jitter is in the noise floor, and the music would mask the jitter. An exception could of course be orchestral music with a huge dynamic range recorded at a very low volume (so the noise floor would be raised). As for how jitter sounds, the video "Digital show & tell" on Xiph.org says quantization noise sounds like tape hiss from analogue tapes, but I might be mixing up quantization noise with jitter (is it the same?). On that website, there's also a file available for download with a 1 kHz tone at -105 dB. When playing that file there's background noise, which I assumed was jitter. In other words, jitter is present in all digital audio, but the amount is so low that you can never hear it except for in those extreme cases mentioned above. I asked Ethan Winer who said:
"Jitter manifests as noise 100+ dB below the music, and is never audible. Nor does it create 'a lack of depth, solidity and a smearing of the stereo image.' You’re thinking of wow and flutter. :->)"

In Ethan Winer's Youtube video "AES Damn lies workshop", he shows the following picture:



My friend's attitude is that jitter is omnipresent and always audible and smears the stereo image etc. (like the comment above), so although he exclusively listens to digital audio he is starting to think vinyl might be the way to go to get rid of the issue of jitter. Surface noise, pops, clicks, etc. from vinyl can be filtered out by our brains, whereas jitter is an omnipresent 'grating' and unpleasant sound.

I of course understand that when creating converters like Dan Lavry does, it's important to minimise jitter as much as possible in order to come closer to creating the perfect product, as well as creating an A/D converter that will have minimal jitter so the recording artists can raise and lower levels on different tracks as much as they like. But as mentioned, I'm only interested in audibility and listening at home – not in the technical aspect (measuring, etc.).
Marantz claims to have Jitter reducing technology. Now I don't think a company as large and as well regarded as Marantz would include a technology in their equipment that didn't have real value ... I trust that their engineers know exactly what they're doing and that reducing jitter matters. I don't think Marantz would spend money on a "non issue".

Re: Is jitter audible and what does it sound like?

Reply #84

Marantz claims to have Jitter reducing technology. Now I don't think a company as large and as well regarded as Marantz would include a technology in their equipment that didn't have real value ... I trust that their engineers know exactly what they're doing and that reducing jitter matters. I don't think Marantz would spend money on a "non issue".

Whether jitter is audible or not, it is perceived as negative to have it in the audio signal. If it can be measurably reduced for small cost then I consider a commercial manufacturer would do it if they could. Of course there may be many variables and factors for a manufacturer to consider in researching and implementing jitter reduction.  I just mentioned the most obvious 2 factors above.

Re: Is jitter audible and what does it sound like?

Reply #85
Marantz claims to have Jitter reducing technology. Now I don't think a company as large and as well regarded as Marantz would include a technology in their equipment that didn't have real value ... I trust that their engineers know exactly what they're doing and that reducing jitter matters. I don't think Marantz would spend money on a "non issue".

"Audiophiles" claim jitter is a problem. Manufacturer wants to sell products to "audiophiles". Manufacturer introduces technology that doesn't really do very much at all and makes no difference to what can be heard. But "audiophiles" see "jitter reduction" and spend lots of money. Manufacturer is happy.

Or....you don't really understand how companies sell products to consumers do you?


Re: Is jitter audible and what does it sound like?

Reply #87
Nice argument from authority, though.
Is 24-bit/192kHz good enough for your lo-fi vinyl, or do you need 32/384?

Re: Is jitter audible and what does it sound like?

Reply #88
I trust that their engineers know exactly what they're doing and that reducing jitter matters. I don't think Marantz would spend money on a "non issue".
Sorry, can't engineer away a mental health issue. Swing and a miss. Wrong authority to appeal.
Btw, it isn't a non-issue, the effect on audiophiles is real. Just not of DUT origin.
Loudspeaker manufacturer

Re: Is jitter audible and what does it sound like?

Reply #89
Or....you don't really understand how companies sell products to consumers do you?
+1

How do we know the engineers thought reducing jitter matters, as opposed to taking marching orders from sales/marketing?

Are we also supposed to trust the "engineers" at Sony?
https://www.sony.com/electronics/hi-res-audio
Is 24-bit/192kHz good enough for your lo-fi vinyl, or do you need 32/384?

Re: Is jitter audible and what does it sound like?

Reply #90
Jitter can be a problem and reducing it always is good but there is a point of dismissing returns and I always found that most of the time the people is clueless about it and think in it a magical way, it effects are not the same in all situations but people think the contrary. Even depending of the technology the effects can vary, as in CD player with a clock signal to the DAC with 1us jitter can have a disastrous effects if it uses a 1bit DAC but at the same time be unnoticeable if it uses a R2R DAC.

The only time that I was able to hear jitter noise in a CD player was in an +20 years old one from a friend (actually his father), I reworked it and the noise and jitter disappeared (caps where bad, some diodes and transistors where also bad an changed the crystal oscillator module as it drifted to much).

Re: Is jitter audible and what does it sound like?

Reply #91
Samples and ABX logs indicating a difference was heard or your post will be binned per rule #8 in our terms of service.

Anecdotes won't cut it.
Is 24-bit/192kHz good enough for your lo-fi vinyl, or do you need 32/384?

Re: Is jitter audible and what does it sound like?

Reply #92
No expert here, but if someone wants to describe how jitter sounds, wouldn't it be very similar to a Doppler Effect. But It would be a Doppler Effect that changes many times per second in very small acceleration changes.

I don't know much about jitter in audio, but I do know about jitter in networking. So I'm extrapolating the concept. In other words, it's my guess.

For Analog sources, jitter would be due to the change of speed of the media during playback. Not so much the overall speed, but tiny acceleration or declaration of the playback speed. Or instability of the playback speed. I would expect this to be inevitable but at the same time mostly negligible. It's part of the nature of electric motors and belt drives, etc.

For digital sources then you have the instability of the clock. Which will depend on the quality of the oscillator. But then again when you have 44,100 samples per second, can you tell which of those samples came a little faster or slower?

An analogy would be the second hand on your analog watch, or second display on a digital watch. Could you tell which seconds in a minute were actually faster or slower than average. Because of the nature of the oscillator and general quality of the watch, all those ticks will not be exactly the same, but over the span of a minute they are expected to keep within a margin of error.

The only way you could probably hear jitter on a real world scenario would be an Analog system which is pretty much failing dew to mechanical flaws. It could be experiencing excessive mechanical resistance. It could be worn out, Or it could be affected by a power problem like low voltage. So you could probably listen it it slow down for longer periods of time and then go back to normal.

On a computer you could probably listen to some sort of jitter if the computer hangs momentarily. Then you might listen to the audio slow down or pause, and then try to catch up. If there is a slow down or catch up it would be jitter. If it just skips during the problem, then you wouldn't actually be able to hear the jitter it would just be a skip.

EDIT:

This is an interesting concept:

"Headbanging jitter.... Someone had jokingly mentioned that jitter that comes from the doppler effect, if you move your head, is probably higher than jitter introduced by the devices themselves."

http://www.sereneaudio.com/blog/headbanging-jitter

Re: Is jitter audible and what does it sound like?

Reply #93
Even depending of the technology the effects can vary, as in CD player with a clock signal to the DAC with 1us jitter can have a disastrous effects if it uses a 1bit DAC but at the same time be unnoticeable if it uses a R2R DAC.

1us of jitter is such a lot that it takes gross incompetence, or even sabotage, to arrive at such figures.

So yes, if you are dealing with this much jitter, I am happy to believe stories that it is audible. But I would discard or repair any piece of equipment that shows this much jitter. I haven't seen anything like that in a device that wasn't defective. And I have seen audiophile devices that were so incompetently designed they produced systematic jitter by design, while at the same time claiming to reduce jitter. Even there, there wasn't this much jitter.

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The only time that I was able to hear jitter noise in a CD player was in an +20 years old one from a friend (actually his father), I reworked it and the noise and jitter disappeared (caps where bad, some diodes and transistors where also bad an changed the crystal oscillator module as it drifted to much).

Well, that looks like a defective device to me. Yet, I'm not sure how you determined that jitter was the problem. Have you got sufficient measurement equipment to find out what exactly was wrong?

Re: Is jitter audible and what does it sound like?

Reply #94
No expert here, but if someone wants to describe how jitter sounds, wouldn't it be very similar to a Doppler Effect. But It would be a Doppler Effect that changes many times per second in very small acceleration changes.

You are right in principle, but it is more useful to speak about it in terms of modulation. Jitter effectively causes phase modulation of the audio signal. This means that the actual effect depends a lot on the nature of the modulating signal, i.e. the jitter signal. Your doppler effect analogy only holds for very low jitter frequencies, i.e. frequencies a few cycles per second at the most. That isn't typical, and you would need enormous amounts of such jitter to produce an effect that is even faintly like doppler.

Normally, the term "jitter" refers to modulating frequencies of 10 Hz or more. In other words, the jitter itself is an audio signal. The term that is used for frequences below 10 Hz is "wander". A doppler effect is wander with an enormous amplitude, so that you actually hear the pitch change. If something like that happens in an audio system, something is very seriously wrong. Like a mechanical problem in an analog tape machine, or a excentric hole in an LP.

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I don't know much about jitter in audio, but I do know about jitter in networking. So I'm extrapolating the concept. In other words, it's my guess.

It is dangerous and misleading to extrapolate this. Jitter that causes modulation is sampling jitter, and it is associated with the sampling clock that drives a converter (ADC or DAC). Jitter in networking is associated with packet transmission, which hasn't got anything to do with the sampling clock.

The only link is the fact that there is variation in timing, in the most general sense. Don't draw any further conclusions from it.

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For Analog sources, jitter would be due to the change of speed of the media during playback. Not so much the overall speed, but tiny acceleration or declaration of the playback speed. Or instability of the playback speed. I would expect this to be inevitable but at the same time mostly negligible. It's part of the nature of electric motors and belt drives, etc.

It is far from negligible. Considerable effort was spent in getting this under control. It is very easy, for example, for mechanical oscillations to build up when tape glides over a pin. Technical term: flutter. Very common. It is actually hard to misdesign a digital device to exhibit such amounts of phase modulation as analog devices frequently do.

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For digital sources then you have the instability of the clock. Which will depend on the quality of the oscillator. But then again when you have 44,100 samples per second, can you tell which of those samples came a little faster or slower?

No, you can't tell from the individual samples. Heck, you don't listen to samples, anyway. You listen to a reconstructed, continuous signal. If anything, you hear a modulation effect. And that's unlikely, because it is quite straightforward to build a good crystal oscillator that has orders of magnitude less jitter than necessary. Much better than anything mechanically analog. If you design digital audio gear and don't know how to do that, you're incompetent. That's not snobbery, that's reality.

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The only way you could probably hear jitter on a real world scenario would be an Analog system which is pretty much failing dew to mechanical flaws. It could be experiencing excessive mechanical resistance. It could be worn out, Or it could be affected by a power problem like low voltage. So you could probably listen it it slow down for longer periods of time and then go back to normal.

It is a bit more common than that, unfortunately. But people have figured out how to deal with it mechanically. Even service people had wow&flutter meters to measure their analog gear, and see if there was a problem. With digital gear those meters are useless. They just don't have a jitter problem that would fall into the range these devices can measure. For digital, you need measurement gear that is more sophisticated than an analog wow&flutter meter.

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On a computer you could probably listen to some sort of jitter if the computer hangs momentarily. Then you might listen to the audio slow down or pause, and then try to catch up. If there is a slow down or catch up it would be jitter. If it just skips during the problem, then you wouldn't actually be able to hear the jitter it would just be a skip.

No, because the relevant oscillator carries on. If the software can"t keep up with it, samples are duplicated or omitted. The effect isn't jitter, but short dropouts.

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"Headbanging jitter.... Someone had jokingly mentioned that jitter that comes from the doppler effect, if you move your head, is probably higher than jitter introduced by the devices themselves."

It is most definitely higher, by many orders of magnitude, but the modulation frequency is quite low.

 

Re: Is jitter audible and what does it sound like?

Reply #95
[A] CD player with a clock signal to the DAC with 1us jitter can have a disastrous effects

I looked up my CD player, a Naim CD5X, on Stereophile's measurement page: It has 241 picoseconds of jitter. Other CD players, both cheaper and more expensive, show jitter figures around the same amount, give or take a few hundred picoseconds (well, give, since jitter amounts in any converter don't go down to 41 picoseconds as far as I know).
One nanosecond is 1000 picoseconds. One microsecond (μs) is 1000 nanoseconds. That would be a hell of a lot of jitter in such a CD player! I'm with Pelmazo on this one - the unit must be defective.
The McIntosh MS750, which is one of the worst units that Stereophile has ever measured for jitter, had 14 nanoseconds of jitter.
The $43,440 Zanden 5000 Mk.IV, which the Stereophile editor called, and I quote, "the worst-measuring digital product [he had] encountered", since everything about it was poorly designed, "only" measured 1018 picoseconds of jitter. But of course, CD-hater extraordinaire Michael Fremer called it the best CD player he had ever heard (and reviewers for other publications were ecstatic as well)!
"What is asserted without evidence can be dismissed without evidence"
- Christopher Hitchens
"It is always more difficult to fight against faith than against knowledge"
- Sam Harris

 
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