Will ripped CDs really equal the musicality of a great CD player?

microstrip

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Stereophile uses the AP system, which is IMO inaccurate for measuring DIRECT JITTER. Not enough bandwidth. It is okay for measuring the jitter effect on the spectrum from the analog output of a DAC, and this is usually what they publish. I do not consider this a good direct measurement for a digital source, since it involves a particular DAC.

I on the other hand use a 7GHz B/W, 50GHz sampling programmable scope with a jitter software package on it and a 75 ohm internal termination to measure jitter directly. This scope with software was $130K when new. The single number that I mention is the standard deviation of the jitter distribution measured over 50K samples. The distribution is created playing a music track, not a single frequency. Here is the jitter plot showing ~7psec of jitter:

https://www.audiocircle.com/index.php?topic=157348.0

I have found these jitter distribution and spectrum plots to be more useful for correlating to sound quality and characterizing a given digital source. The shape of the distribution matters and the standard deviation matters, as well as the spectral distribution. I have shared this with John Atkinson, who I know, but curiously have gotten no response.

Steve N.
Empirical Audio

A very interesting and honest post. The main point for me is exactly the subjective correlation with sound quality. As far as I know there is no data on these subject, except from those who say that jitter at the levels we are debating is inaudible. :( An sorry, but when you say " I have found " it is you against all the large community that uses the AP system, not just Jonh Atkinson - he is just an user of the AP. Do you have any details about how you establish correlations with sound quality that you want to share with us?
 

Empirical Audio

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You don't need a 'couple of seconds', but rather just enough to handle the speed variations in the drive. It is sometimes nice to be able to handle the 3sigma case, but that isn't always in the budget. Back in the day, video tape decks didn't need 'seconds' of delay, but just enough time to incorporate the variations in speed. Later on, with memory being cheap, then they just did the brute force frame store thing. The large frame stores could impart a frames worth of delay or more (1/25 or 1/29.97 second.) On average, the delay was one half the frame or field rate -- but that isn't really necessary in the straight FIFO design (full buffering only needed if the CD speed cannot be controlled by hardware.)

It is all FIFO queueing -- I successfully do it all of the time, and don't get jitter (other than the last timing clock in the chain.) I can get errors -- but not jitter.

John

Like most things, with FIFO queuing, the devil is in the details. I would argue that it's extremely difficult to achieve really low jitter (like my 7psec), when using a FIFO design, UNLESS the source is willing to throttle the data into the FIFO under the control of the FIFO (this is a "PULL" technique rather than a "PUSH" technique) or you are willing to live with out of spec oscillator frequencies.

If you are talking about a typical PUSH technique where the data is coming whether the FIFO is ready or not, then achieving really low jitter is very difficult. Here's why:

There are only three methods for making this work (avoiding FIFO overruns and underruns) and they all include methods to vary the Master Clock frequency:

1) pull the data from the FIFO output using a PLL controlled oscillator. This will sync with the input data flow and avoid overruns and underruns.

2) pull the data from the FIFO using an oscillator that can be "pulled" slightly off the nominal frequency, both higher and lower. This "bang-bang" system keeps the FIFO from overrunning by changing to a higher frequency and underruning by changing to a lower frequency.

3) pull the data from the FIFO using multiple clocks that are slightly above and below. The clock that is selected is based on whether the FIFO is trending to underrun or overrun at any point in time.

Variable clock frequency systems create higher jitter than free-running clocks do. Both solutions (1) and (2) are guilty.

If you are willing to live with changing frequency and out of spec frequency on your data stream, then solution (3) can deliver very low jitter.

The moral of the story is that the only true low jitter solutions are those that:

1) resample the data and establish a new Master Clock frequency

or

2) rely on the source throttling the data in a handshake with the device, such as async USB and Ethernet interfaces, so that the real Master Clock is in the device, not the source.

Steve N.
Empirical Audio
 

Empirical Audio

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A very interesting and honest post. The main point for me is exactly the subjective correlation with sound quality. As far as I know there is no data on these subject, except from those who say that jitter at the levels we are debating is inaudible. :( An sorry, but when you say " I have found " it is you against all the large community that uses the AP system, not just Jonh Atkinson - he is just an user of the AP. Do you have any details about how you establish correlations with sound quality that you want to share with us?

That's difficult and work in progress. What I have found is that multiple peaks with significant separation in the jitter distribution usually causes a "hardness" in the sound quality, even if the peaks are only 30 psec each in width. I have measured other devices and experienced this.

The other thing I have noticed is that even very wide jitter distributions in one peak can sound very euphonic, but one thing is for sure, the imaging is crap at high frequencies.

These are the only two solid observations I have made so far, other than noting that even a change from 20psec to 7psec is immediately obvious in the sound quality, particularly the imaging. You must understand that I have an extremely resolving system. My customers however also noticed quite a difference when going from 20psec to 7psec of jitter. This really hard to believe, even for me. I had expected that less than 1sec of jitter would be sufficient and anything below that would be inaudible. I continue to be surprised in this business.

Steve N.
Empirical Audio
 

Al M.

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Sep 10, 2013
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Hi Al,

Must remember humour does not translate via the internet, or that I suck at it, or both.

Yeah, I knew it was tongue in cheek but I took the opportunity to post a serious answer.

Most paths are often not linear. Mine has been very zig-zagged, with steps both sideways and back and up and down. I think most experiential pursuits inevitably are, because as true as it that we change paths, the path changes us.

No disagreement here.
 

morricab

Well-Known Member
Apr 25, 2014
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Well, making CD-R copies was all fun and games pre-children, but post-children it ceased to be a productive endeavour and in any case, I rediscovered vinyl, which happened to also coincide with many of the artists I like forgoing physical media releases. I'm mostly a record and downloading kinda guy these days. Heck, I'm even considering buying a cassette deck.



Thanks, but my JBL GO only has a USB port.



There's a path?

Best,

853guy

You should try to hear a Nakamichi ZX-9. My partner got one and its really darn good!
 

853guy

Active Member
Aug 14, 2013
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You should try to hear a Nakamichi ZX-9. My partner got one and its really darn good!

Hey morricab,

Currently a toss up between the ZX-9, ZX-7 or CR-7.

Apologies for talking about cassettes in a CD thread.

Carry on, gentlemen.

853guy
 

John Dyson

Member
Jul 2, 2018
41
1
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Like most things, with FIFO queuing, the devil is in the details. I would argue that it's extremely difficult to achieve really low jitter (like my 7psec), when using a FIFO design, UNLESS the source is willing to throttle the data into the FIFO under the control of the FIFO (this is a "PULL" technique rather than a "PUSH" technique) or you are willing to live with out of spec oscillator frequencies.

If you are talking about a typical PUSH technique where the data is coming whether the FIFO is ready or not, then achieving really low jitter is very difficult. Here's why:

There are only three methods for making this work (avoiding FIFO overruns and underruns) and they all include methods to vary the Master Clock frequency:

1) pull the data from the FIFO output using a PLL controlled oscillator. This will sync with the input data flow and avoid overruns and underruns.

2) pull the data from the FIFO using an oscillator that can be "pulled" slightly off the nominal frequency, both higher and lower. This "bang-bang" system keeps the FIFO from overrunning by changing to a higher frequency and underruning by changing to a lower frequency.

3) pull the data from the FIFO using multiple clocks that are slightly above and below. The clock that is selected is based on whether the FIFO is trending to underrun or overrun at any point in time.



Steve N.
Empirical Audio

Aremt you forgetting that the data is the clock and the clock is the data, and the pll in detection is only used to set the sampling point. (I know, I have implemented self clocked schemes from scratch.)
If the pll gets out of sync, then you are 'dead meat', because the signal is either a logical 1 or 0. An unlocked pll doesn't allow data recovery. An imprecise sample will result in an error or not when coming directly off the media. A CD doesn't hav analog data where the sampling point might be important for accuracy beyond the simple 1 or 0. The sampling point accuracy only determines the reliability of the data. There isn't an in between for the data itself. If there is sampling point jitter, then there is a correct detection or not -- not an in-between. There CAN be a statistical liklihood of accuracy, but that is the only real 'percentage' associated with the data. This would be the digital equivalent of SNR.

Another thing, the electronic circuitry used to read the optical device needs pre-amplication, but that also resolves to a 1 or 0. During the actual detection process, some more stats might be done, and merge the details of the PLL with the analog result of the detection -- again, there has to be a resolution to 1 or zero for the data, and the clock comes along with it. The clock on disk and the data-on-disk don't get out of sync, but if the sythesized clock from the PLL gets out of sync -- then it is an error. If the sampling point is off too far, then there is also an error. Jitter in the sampling point only increases the liklihood of error, not causing jitter in the resulting data.

So, here is what you have: data can be 1 or 0, the pll can be 'locked' or 'unlocked', and if achieving lock, the sampling point can be 'accurate enough', or 'inaccurate.' There is no 0.75 for the value, it is 0 or 1. The clock for the data does come from the pll (or the disk in reality), but the accuracy of the data sampling point doesn't result in a more or less accurate answer for that one bit, it only determines the likelihood of correctness. Now, there can be a relative likelihood of correctness, but we are not reading data that is statistically encoded, but rather the real 1 or 0 that had been recorded. (for analog laser disks, the statistics can produce video noise, but that kind of noise doesn't happen on audio discs unless it is so bad to cause an error.)

If you are talking about the pll/feedback loop for the data buffering, then that is also kept in sync as I had described before in another posting -- the rotation of the medium is logically very similar to a variable speed FIFO in its own right, and it is used to feed a data buffer fifo clocked by the data coming off the disk on one side, and the rock-stable system clock on the other side of the data buffer fifo. At that point, there is NO jitter other than the relatively rock-solid system clock.

PS: I am pretty sure that I didn't make this clear -- there are effectively two different PLLs (depending on implementation). There is the RAW data recovery PLL as most of my posting talks about -- it locks to the on-disk signal to almost something like a radio signal, except it is a series of pulses with a specific frequency and kind of pattern. (The simplest think like this is a Manchster encoded scheme -- Wiki probably describes that.) Also, there is a second 'phase lock', and that is for the rotational behavior of the drive. It helps to keep the higher level data rate correct, and the data FIFO full without overflowing. So, we have both the data signal (bit by bit), and the data rate (packets of some kind, might be bytes.) There might be a way of implementing both PLLS as the same, but the simplest implementation is to both synchronize TO the data on the disk, and synchronize the rotation to the required data clock out rate. The platter rotation can have a lot more timing slop than the data clock, and most likely the platter PLL runs more slowly than the data PLL. (AGAIN, it might be possible to merge the two somehow, but tightly tieing the raw data with the rotation might not be a good idea.) If you read about Manchester encoding, you can see generally how the clock and data can be integrated into the same stream.



John
 
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Empirical Audio

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Aremt you forgetting that the data is the clock and the clock is the data, and the pll in detection is only used to set the sampling point. (I know, I have implemented self clocked schemes from scratch.)
If the pll gets out of sync, then you are 'dead meat', because the signal is either a logical 1 or 0. An unlocked pll doesn't allow data recovery. An imprecise sample will result in an error or not when coming directly off the media. A CD doesn't hav analog data where the sampling point might be important for accuracy beyond the simple 1 or 0. The sampling point accuracy only determines the reliability of the data. There isn't an in between for the data itself. If there is sampling point jitter, then there is a correct detection or not -- not an in-between. There CAN be a statistical liklihood of accuracy, but that is the only real 'percentage' associated with the data. This would be the digital equivalent of SNR.

Another thing, the electronic circuitry used to read the optical device needs pre-amplication, but that also resolves to a 1 or 0. During the actual detection process, some more stats might be done, and merge the details of the PLL with the analog result of the detection -- again, there has to be a resolution to 1 or zero for the data, and the clock comes along with it. The clock on disk and the data-on-disk don't get out of sync, but if the sythesized clock from the PLL gets out of sync -- then it is an error. If the sampling point is off too far, then there is also an error. Jitter in the sampling point only increases the liklihood of error, not causing jitter in the resulting data.

So, here is what you have: data can be 1 or 0, the pll can be 'locked' or 'unlocked', and if achieving lock, the sampling point can be 'accurate enough', or 'inaccurate.' There is no 0.75 for the value, it is 0 or 1. The clock for the data does come from the pll (or the disk in reality), but the accuracy of the data sampling point doesn't result in a more or less accurate answer for that one bit, it only determines the likelihood of correctness. Now, there can be a relative likelihood of correctness, but we are not reading data that is statistically encoded, but rather the real 1 or 0 that had been recorded. (for analog laser disks, the statistics can produce video noise, but that kind of noise doesn't happen on audio discs unless it is so bad to cause an error.)

If you are talking about the pll/feedback loop for the data buffering, then that is also kept in sync as I had described before in another posting -- the rotation of the medium is logically very similar to a variable speed FIFO in its own right, and it is used to feed a data buffer fifo clocked by the data coming off the disk on one side, and the rock-stable system clock on the other side of the data buffer fifo. At that point, there is NO jitter other than the relatively rock-solid system clock.


John

I'm not forgetting anything. We will just have to agree to disagree on this.

Steve N.
 

Pb Blimp

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Although I disagree with most of John Dyson points, it is possible to erase the "past memory" of jitter if you accept a delay of a few seconds. I never understood why the industry never embarked on it. Vinyl lovers easily accept a few seconds wait while their tonearm goes down ... :cool:

It would be very helpful if you could point out to which of John's points you are referring.
 

microstrip

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That's difficult and work in progress. What I have found is that multiple peaks with significant separation in the jitter distribution usually causes a "hardness" in the sound quality, even if the peaks are only 30 psec each in width. I have measured other devices and experienced this.

The other thing I have noticed is that even very wide jitter distributions in one peak can sound very euphonic, but one thing is for sure, the imaging is crap at high frequencies.

These are the only two solid observations I have made so far, other than noting that even a change from 20psec to 7psec is immediately obvious in the sound quality, particularly the imaging. You must understand that I have an extremely resolving system. My customers however also noticed quite a difference when going from 20psec to 7psec of jitter. This really hard to believe, even for me. I had expected that less than 1sec of jitter would be sufficient and anything below that would be inaudible. I continue to be surprised in this business.

Steve N.
Empirical Audio

Thanks, but as your system is mostly custom, non reproducible and unknown to 99.99% of WBF readers you are in a desert island with your customers claiming against an whole audiophile community concerning jitter. I hope that sometime in the future you are able to present us something we can debate in a positive sense.

Unfortunately in digital audio it seems that our ears must be the unique judge at the buying moment. My only experience with with high jitter digital is the Metronome system and I can assure you it has exceptional imaging at high frequencies.
 

Empirical Audio

Industry Expert
Oct 12, 2017
1,169
207
150
Great Pacific Northwest
www.empiricalaudio.com
Thanks, but as your system is mostly custom, non reproducible and unknown to 99.99% of WBF readers you are in a desert island with your customers claiming against an whole audiophile community concerning jitter. I hope that sometime in the future you are able to present us something we can debate in a positive sense.

Unfortunately in digital audio it seems that our ears must be the unique judge at the buying moment. My only experience with with high jitter digital is the Metronome system and I can assure you it has exceptional imaging at high frequencies.

Since listening tests are purely subjective, the only evidence I have is anecdotal, from me and all of my customers. We cannot all be wrong. Just because I don't advertise means nothing. That is why I offer 30-day money-back on the majority of my products. It's low-risk to try them. I have been in business for 22 years and have Golden-Ear awards, many best of shows and lots of professional reviews. Some of the most famous names in audio make crap IMO. I don't want to be a big company or even well-known, just the best. I'm not in this to get rich or hand down my business to relatives.

BTW, I have modded in the past many of the pre-existing reclockers, including Metronome product, Big Ben and Monarchy DIP. None of them delivered what I would consider exceptional imaging and focus at high frequencies. It takes extremely low jitter to get this.

I notice you have Vivaldi front-end. Very nice. At one RMAF, rooms on both sides of my conference room used these, so I got to hear them. I much prefer my own Overdrive SX.

Steve N.
Empirical Audio

Steve N.
Empirical Audio
 
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