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Is an external clock always better? Audio Interfaces
Old 26th July 2015
  #1
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mrmike186's Avatar
 

Is an external clock always better?

Let's say something like a Black Lion mkII on an RME Fireface UFX or even a cheapie Behringer. I realize using multiple units benefit having one master clock but what if you are using just one unit? At what point is the mk2 not an upgrade in sound on a single stand alone unit?
Old 26th July 2015
  #2
Lives for gear
 

All depends on the quality of the internal clock. It can make it better though sometimes it just makes it different.
Old 26th July 2015
  #3
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EastWest Lurker's Avatar
 

In a White Paper, Dan Lavry, who designs some of the best converters ut there, say an internal crystal will always have the least jitter unless it is very poorly designed, and that most are pretty good. So if you use an external clock to a single interface you are introducing more jitter and unless for some reason you prefer that sound, which I guess is possible, you are making things worse. External clocks obviously are fine for clocking multiple interfaces.
Old 26th July 2015
  #4
Slaving to an external clock source almost always degrades the performance of the slaved unit, vis a vis running under its own internal clock.

The article linked below explains why and demonstrates the results with real performance testing of a handful of representative clocks and converters. As you can see, only the very best converters (we're not talking Apogee) have adequate clock recovery to perform transparently when slaved to an external source.

Sadly, there's a well-known converter and clock company (ahem) that still seems to want to promote the baseless notion that signal accuracy is improved by external clocking -- but that company's products are tested in the above set of tests and the falseness of that notion soundly demonstrated.

When confronted, their representatives have, in the past, said they are suggesting such use isn't necessarily more accurate -- it sounds better. To someone.

But if it does, it must sound better because they like the sound of increased jitter.

Hugh Robjohns in Sound-onS0und: Does Your Studio Need A Digital Master Clock?
Old 26th July 2015
  #5
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EastWest Lurker's Avatar
 

Exactly. I had a huge fight here years ago with a rep from a company i will not name. He conceded that his product introduced more jitter but said it was where it introduced the jitter that was their secret sauce and that it was possible to introduce more jitter but be perceived by the listener as less jitter. And that if a listener heard improvement, who was his company to tell them they didn't?

I responded that at that point I would just as soon fly to the Garden of Good and Evil and at midnight, start swinging dead cats around
Old 26th July 2015
  #6
Quote:
Originally Posted by EastWest Lurker View Post
Exactly. I had a huge fight here years ago with a rep from a company i will not name. He conceded that his product introduced more jitter but said it was where it introduced the jitter that was their secret sauce and that it was possible to introduce more jitter but be perceived by the listener as less jitter. And that if a listener heard improvement, who was his company to tell them they didn't?

I responded that at that point I would just as soon fly to the Garden of Good and Evil and at midnight, start swinging dead cats around
I remember that dialog. (I had to go look up Garden of Good and Evil so it stuck in my mind.)

FWIW, our mutual pal bailed that company for a bigger company (whose own position, as both converter and clock maker, and backed up by a white paper specifically on the topic, was that slaving-to-improve-sound is nonsense). I'd like to think he's happier there (if he's still there). I suspect I would be. I've been a marketing guy who had to play fast and loose with the truth on direct order from my bosses and it really did not sit well with me.


Anyhow, since the Sound-on-Sound article came out with it's real world tests and thorough explanations, this particular snake-oil has lost a great many of its one-time true-believers. An encouraging sign.

_____________________

PS to anyone still unclear... Of course, as noted, if you have multiple converters, there must be a single master clock source. It can be a standalone clock or one of the converters. Proper clock cabling and termination is critical to minimizing jitter. And, as one can see, the truly good converters have excellent clock recovery. But not so much those of the company that started this snake oil nonsense with a series of 'celebrity producer' endorsements talking about the improved sound from slaving to their well-known standalone clock. THEIR clock recovery at least beats Behringer but is not nearly as good as the best.
Old 26th July 2015
  #7
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So what is that company?
Old 26th July 2015
  #8
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EastWest Lurker's Avatar
 

Quote:
Originally Posted by bad jitter View Post
So what is that company?
Not gonna go there, bygones.
Old 26th July 2015
  #9
Lives for gear
Quote:
Originally Posted by EastWest Lurker View Post
... an internal crystal will always have the least jitter unless it is very poorly designed, and that most are pretty good. So if you use an external clock to a single interface you are introducing more jitter...
Quote:
Slaving to an external clock source almost always degrades the performance of the slaved unit, vis a vis running under its own internal clock.

The article linked below explains why and demonstrates the results with real performance testing of a handful of representative clocks and converters. As you can see, only the very best converters (we're not talking Apogee) have adequate clock recovery to perform transparently when slaved to an external source.
Well this is depressing.

I have a rom workstation keyboard that has spdif digital audio out. My audio interface has an spdif in. "Excellent!", says I - I can connect the two and have an absolutely perfect digital transfer of the signal from the keyboard into my DAW. No need to go D/A then A/D. I will get an exact copy of the rom waveform in my DAW.

But apparently it's just a dream. One of them has to be master, the other slave. Which, apparently, means my perfect transfer is going to have additional jitter introduced into it??

I suppose one could ask if this additional jitter adds more or less loss of fidelity to the original than the a/d-d/a process.
Old 27th July 2015
  #10
If you have 2 or more devices there is nothing you can do about it. Don't worry about jitter in that case. Just make sure the digital devices are good enough and you'll be fine. If you have good converters you might even prefer an analog connection for the keyboard.
I fully agree with Jay and theblue1 btw, an external clock only makes sense when using multiple digital devices to have one master directly connected to all slaves. Some people indeed prefer an external clock to their sometimes already very good converters, but this is subjective and probably even perception bias.
Old 27th July 2015
  #11
Gear Nut
 

These are the kinds of upgrades you can think about when your monitoring chain (room, speakers) are top notch an cannot be improved any further.
Old 27th July 2015
  #12
Gear Nut
 

Quote:
Originally Posted by DAW PLUS View Post
Some people indeed prefer an external clock to their sometimes already very good converters, but this is subjective and probably even perception bias.
I'd say it's perception bias in 95% of all cases.

The difference is approaching zero - 1000s of dollars have been spent - it sounds soooooo much better.
Old 27th July 2015
  #13
Quote:
Originally Posted by EastWest Lurker View Post

I responded that at that point I would just as soon fly to the Garden of Good and Evil and at midnight, start swinging dead cats around
It's a DAMN good thing I was in between mouthfuls, eating my morning cereal
Old 27th July 2015
  #14
Your money is better spent on higher quality AD and DA converters. External Clock is not a sound processor
Old 27th July 2015
  #15
Quote:
Originally Posted by DAW PLUS View Post
If you have 2 or more devices there is nothing you can do about it. Don't worry about jitter in that case. Just make sure the digital devices are good enough and you'll be fine. If you have good converters you might even prefer an analog connection for the keyboard.
I fully agree with Jay and theblue1 btw, an external clock only makes sense when using multiple digital devices to have one master directly connected to all slaves. Some people indeed prefer an external clock to their sometimes already very good converters, but this is subjective and probably even perception bias.
Not to do the mutual-that's-good-advice thing, but that's good advice.

If you have two devices, there's no other option, there can only be one master clock source -- but with any luck, the jitter will be quite low and have no discernible effect. If one looks at the jitter charts in the article, even the worst of it is pretty low in level compared to the overall signal.

People with complex rig with stacks of converters have to worry more about this stuff more, but your situation should be pretty simple. If it sounds good, it probably is good.

The only reason folks belabor this is really the whole improve-my-rig-by-using-an-external-clock meme, which has caused people who didn't need an external clock to sometimes spend over a thousand dollars/Euros for something that will almost certainly not improve signal accuracy.


With regard to the company, they're well-known, and many people really seem to legitimately like their converters -- and the name will probably be familiar, particularly to those who've read the article.

All that said, with regard to the devices (clocks and converters -- since it's the converter's clock recovery which is the tricky part, as noted) bench-tested in the article, the performances are there in black and white. None of them are awful. But if one looks at the performance breakdown and compares prices he will see that, in general terms, you get what you pay for. The low end is adequate, the middle pretty good, the top, pretty damn stellar. (But you pay for it.)



If one has a complex rig with a lot of converters, it may be logistically more convenient to use a central, external clock. But for small rigs with a few converters, one can generally get good performance by using the presumed 'best' converter as the master and slaving to it. (This has the added advantage of keeping the master device on its own clock, likely optimizing performance.)

And for a single converter -- in most cases, just let it be its own master.

Last edited by theblue1; 27th July 2015 at 04:02 PM..
Old 27th July 2015
  #16
Quote:
Originally Posted by DAW PLUS View Post
If you have 2 or more devices there is nothing you can do about it. Don't worry about jitter in that case. Just make sure the digital devices are good enough and you'll be fine. If you have good converters you might even prefer an analog connection for the keyboard.
I fully agree with Jay and theblue1 btw, an external clock only makes sense when using multiple digital devices to have one master directly connected to all slaves. Some people indeed prefer an external clock to their sometimes already very good converters, but this is subjective and probably even perception bias.
I use multiple computers (actually only 3 at 'this' time) each with their own audio interface. I also use coaxial s/pdif digital audio between them. I have extra interfaces that I've collected at my disposal, and the manufacturer (Aardvark) has allowed for 'up to' 4 of their interfaces to be installed in each computer (though my mobo only has 3 PCI slots, so I'm limited to 3). Only one of my machines actually have 2 interfaces installed. When I get around to installing 2 or more interfaces per machine, I'm thinking this will potentially pose extra problems.

I can of course use one of my interfaces in the chain as my master clock, or use a dedicated external clock as my master. I've yet to have the time to set it all up for what my systems 'can be' to compare just using an interface for the clock master, or the dedicated clocking machine.

In addition, I've only recently learned that daisy chaining word clock and/or using "T" connectors is NOT the way to go, but a word clock distribution unit, allowing individual word clock outputs from it, to each digital device.
As said, it may at some point be the lesser of evils to start using analog I/O more as systems get more & more complicated. Aardvark at one time, were known for their good clocking (so I've read many times anyway), and were also well revered for their quality analog I/O. They sound very good to my ears anyway.

I'm still learning about all this here, and have a lot of experimentation to do with multiple PC's with their own multiple audio interfaces. If I only had unlimited time on my hands, and didn't have to work for a living!
Old 27th July 2015
  #17
Lives for gear
Wait a minute - have I unwittingly introduced a non sequitur to the topic?

In the case I describe, the digital audio is being generated by the keyboard, which is using its own internal clock. The audio interface is slaved, but does it matter? The keyboard should be sending data in the form (amplitude, time) which is simply recorded in a wav file associated with a track. No conversion at the audio interface is taking place. Amplitude-time pairs are simply being passed through to the DAW. This should be just like transferring a data file. No?
Old 27th July 2015
  #18
Quote:
Originally Posted by musicus View Post
Wait a minute - have I unwittingly introduced a non sequitur to the topic?

In the case I describe, the digital audio is being generated by the keyboard, which is using its own internal clock. The audio interface is slaved, but does it matter? The keyboard should be sending data in the form (amplitude, time) which is simply recorded in a wav file associated with a track. No conversion at the audio interface is taking place. Amplitude-time pairs are simply being passed through to the DAW. This should be just like transferring a data file. No?
Unfortunately, not exactly. (But, again, you probably don't have any significant problems; if you liked your signal before you knew all this stuff, it's still just as good. )

S/PDIF embeds the clocking into the signal -- but since it's intended as realtime audio transfer and the receiver may need to fold that signal in with other signal, it must be able to extract a reasonable clock signal.

A couple excerpts from the Wikipedia article on S/PDIF might help:

Quote:
S/PDIF is used to transmit digital signals of a number of formats, the most common being the 48 kHz sample rate format (used in DAT) and the 44.1 kHz format, used in CD audio. In order to support both systems, as well as others that might be needed, the format has no defined data rate. Instead, the data is sent using biphase mark code, which has either one or two transitions for every bit, allowing the original word clock to be extracted from the signal itself.

[...]

The receiver does not control the data rate, so it must avoid bit slip by synchronising its reception with the source clock. Many S/PDIF implementations cannot fully decouple the final signal from influence of the source or the interconnect. Specifically the process of clock recovery used to synchronize reception may produce jitter.[6][7][8] If the DAC does not have a stable clock reference then noise will be introduced into the resulting analogue signal. However, receivers can implement various strategies which limit this influence.[8][9]

TOSLINK cables, unlike coaxial cables, are immune to ground loops and RF interference.[10] TOSLINK cables may suffer permanent damage if tightly bent.
I included the last paragraph because back when I had a somewhat complex lightpipe cabling setup I accidentally 'crimped' a long $40 lightpipe and had to buy a new one. (The results were not ambiguous in my case; the slaved device couldn't sync and receive data properly.)
Old 27th July 2015
  #19
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Hmmmm....so, extreme measures - have the keyboard save the performance on-board as a wav file, self-clocked, then make a copy of that wav file onto a usb key and load it into the DAW as an audio track?
Old 27th July 2015
  #20
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I was just talking about this topic with a friend of mine, that uses the a BLA External clock. He seems to prefer his MOTU converters, when clocked to the BLA. I explained, what most folks in here have and sent him the SOS article.

Then he pointed me to this quote from BLA:

Quote:
"When we introduced the Micro Clock mk2, we didn’t anticipate the amount of demand and controversy that managed to accompany it. External clocking is certainly a hot button issue. Some folks maintain that there’s no basis for it; that it’s a sort of modern “emperor’s new clothes.” The reasoning behind this is that the device being clocked externally will simply filter the incoming clock signal through its phase lock loop, thereby eliminating any sort of benefit associated with the superior clock. In addition, the simple act of accepting the incoming signal and creating a new signal that’s in phase will add some jitter. The biggest problem with this theory is that we know nothing about the PLL filter in question; it’s completely hypothetical. Many PLL’s in pro audio are designed to filter out unwanted signals that are outside of the desired bandwidth, although some are configured to filter out unwanted harmonics that lie within the signal’s frequency band. It’s incredibly rare to find one that does both at the same time. In the case of the Micro Clock mk2, there is very little undesirable in-band or out of band content (below 10 picoseconds using a Delta Sigma average). There is, however, an abundance of desirable harmonically related in-band spectral content; more so than the average internal clock. No PLL filter is designed to remove these desirable harmonics; they’re busy trying to remove the unwanted stuff.
Simply put, the Micro Clock mk2 will not only provide an audible improvement to your conversion process, but it will do it as well or better than any other external clock on the market today"
I put in bold the exact part of this explanation that I have an issue with. It seems that the author of this quote is implying that the PLL passes the audio signal itself, and not the time signal from the reference clock. So, in that conversation "in-band" and "out of band" refer to the frequency domain that the clock operates in (~ Mhz), which is band limited to limit the time it takes for the loop to sync with the clock.

I can't imagine the clock signal would ever need "to filter out unwanted harmonics that lie within the signal’s frequency band", since there probably aren't any unwanted harmonics in the time signal generated by the master clock, in the first place.

I'm no expert, but BLA's explanation does not sit right with me.
Old 28th July 2015
  #21
Quote:
Originally Posted by telegramsam View Post
I was just talking about this topic with a friend of mine, that uses the a BLA External clock. He seems to prefer his MOTU converters, when clocked to the BLA. I explained, what most folks in here have and sent him the SOS article.

Then he pointed me to this quote from BLA:



I put in bold the exact part of this explanation that I have an issue with. It seems that the author of this quote is implying that the PLL passes the audio signal itself, and not the time signal from the reference clock. So, in that conversation "in-band" and "out of band" refer to the frequency domain that the clock operates in (~ Mhz), which is band limited to limit the time it takes for the loop to sync with the clock.

I can't imagine the clock signal would ever need "to filter out unwanted harmonics that lie within the signal’s frequency band", since there probably aren't any unwanted harmonics in the time signal generated by the master clock, in the first place.

I'm no expert, but BLA's explanation does not sit right with me.
I'm no digital electronics engineer, but I'll be darned if I can figure out a way to interpret that BLA quote that makes any real sense or seems in any way credible in its blanket guarantee of improvement.
Old 28th July 2015
  #22
Lives for gear
From Michal Of Mytek

Right on. External clock is in most cases just a distortion inducing device and many people seem to like this coloration and call it improvement.

All evidence (in this case FFT distortion plots) has always proved only that.

External jitter induced by external clock typically emphasizes midrange what is then mistaken for "warmth" or "forward" or "focus", while at the same time bass and highs suffer loss of resolution.

Money would be better spent on a nice tube EQ instead.

External clock can make sense when used to synchronize complex digital systems but it "improving" sound is the biggest audio myth ever.

Michal, Mytek New York



From Jim Williams Of Audio Upgrades



This is true. Michal is very good at designing low jitter clocks. We have had many discussions about these issues. He is able to produce an internal clock with less than 10 ps of jitter. However, run that down 3~4 inches of PCB trace and it goes up to 100 ps. Run that down an external cable and all hell breaks loose.

This is why the clock signal is regenerated internally even if using a so called "clean" external clock. Your digital gear will never get those low jitter specs of your master external clock due to these issues.

Or, just listen to Dan Lavry.


From Dan Lavry Of Lavry Engineering

Say you have a movie camera designed to take 100 picture frames per second, thus a frame every .01 second. You are pointing the camera at an ball moving from left to right at a constant speed, and you take a whole second of that motion, that is 100 picture frames. When you “play it back” with a movie projector that runs a picture each .01 second, everything would “be fine”, as intended.

But let us say that the camera is very “unsteady”. It takes a picture, then it waits .05 seconds, then it takes 5 frames within say .001sec, then a couple of frames at .01 second…. When you play it back, the projector “does not know” what happened at the camera, and the ball may like it is slowing at mid air for a brief time, then it zooms real fast some distance…. That is distortion due to timing error - time jitter. Note that if the camera was OK but the projector had jitter, that also would be a problem. So jitter counts at 2 places - at the camera (which is analogous to the AD), and at the projector (which is analogous to the DA). Jitter is important at the converters.

In one sense, jitter at the AD is more important, because once it takes place; it is in the signal forever. One can replace a bad DA with a good one, and that will eliminate the jitter issue of a poor DA, but what the AD does can not be undone.

Analogies can be misleading. In the case of movies, with enough still frames per second, the eye makes it looks like continues motion. In the case of conversion, it is the analog circuitry that takes the samples and makes them into a continues wave. But I chose the analogy of video, because audio and video (as well as many other applications) are fundamentally based on equal and precise time intervals. The time between each adjacent sample should be exactly the same, and if it is not, there is jitter, which will distort the outcome.

I said that jitter is important at the conversion. What about jitter in transferring say data from AD to a computer hard drive? The answer - it is not important, because we are just moving data from one place to another. You can move one frame every second, very slow indeed, or move a million frames a second, very fast. You can move half the data now, wait a while then move the rest of it… It does not matter, because you are not viewing it. But one you play it back you need the timing to be clocked precisely.

But some manufactures and sellers of clocks wanted to sell clocks, so they decided to convince the world that you need to clock everything. And with enough advertizing money, they where pretty successful doing just that. There are times when you need to use external clock box - when you want to have a lot of gear (AD channels) work together. But as long as you do not need external clock and you can use internal, use internal. It is not only cheaper, it is better!

What you need is the “best clock circuit you can make” that is very steady to be very near your AD circuit - short connection, good grounding… That is internal clock.

Say you take the same “best clock circuit you can make” and put it in another chassis. Will that be better? Not, it will be worse. You now have to deal with 2 chassis thus grounding issues. You have a cable that can pick interference, you have a cable termination imperfection, a cable driver, a cable receiver, and I did not even start… By the time your clock arrives from the clock box, it has so much jitter that it requires some “jitter cleaning circuitry” - typically a PLL circuit…. I pride myself for making very fine external clock circuitry, but no way can I make the external clock circuitry be as good as internal. Almost as good, yes, but never as good.

However, the clock BS’ers are still arguing that their external clock will improve the sound. There is some claim of a “proprietary clock signal” that will make things better. That is a crock if there ever was one! The clock box to the AD connection is a ONE WAY street. The clock “DOES NOT KNOW” what the AD is doing. What kind of a clock box signal is going to improve ALL the following an Ad's:

1. AD with a lot of jitter induce by 60Hz power line
2. AD with little jitter induced by 60Hz power line
3. AD with jitter induce from digital circuit noise
4. AD with jitter due to nearby radio transmitter
5. AD with jitter due to nearby power tools
6. AD with jitter induced from the digital audio data
7. AD with almost perfect timing
8. AD that is powered off…

This is analogous to a doctor that can cure all illness, doing so without any information about the patient…

One of the main offending marketing BS guys said that you can take a tone and have it sound better with jitter. You can alter a fixed tone with jitter, and can argue that you like it, or that you do not like it. But the alteration has to be deliberate for a specific constant tone (including fixed amplitude). You change the tone and the distortion changes... Jitter distortions are very complicated, and they are an INTERACTION between the clock timing AND THE MUSIC. The last I heard, music is not a constant fixed tone The simplest of jitter (random jitter) will increase your noise floor. More complex jitter makes for all sorts of undesired at frequencies that depend on the music, but at frequencies that are not musical harmonics, thus sound bad….

I first stated that internal clock is best a few years ago, and had to deal with a lot of attacks on a forum I was moderating. I insisted that the technical folks come in, instead of the marketing types, and sure enough, the technical types backed off after a short “fight” because they had no leg to stand on. A couple of years later, Digidesign wrote a paper about clocks, and they second me by saying that internal clocks are the best (when you can use internal clocks). I pointed that out and that brought about more attacks… The low jitter crock (I meant to say clock) goes on, and people are clocking with external clocks a lot of stuff they do not need to.

When your AD is using the internal clock for conversion, you are doing the best you can. The data sent forward to a computer, DAW or what not, is “after the conversion” so it does not need to be clocked with special care for jitter, and a “standard” link (say AES or SPDIF) is just fine for data transfer.

There are times when you need to use external clock, and when you need to, use external, when it is a needed trade off. For example, say you want to clock 2 or more AD chassis together... But other then that, internal is the better way to go!

Regards
Dan Lavry"

&

First, about clock absolute accuracy:

If you view it from the point of view of pitch, clock accuracy of the cheapest crystal is more then good enough, because the ear can not hear 1 cent of pitch deviation, not even a sudden 1 cent pitch. A cent is around 1 part in a hundred between 2 notes on the tempered scale. So you end up with somewhere around 400 parts per million or so yielding a much better accuracy then needed to hear a pitch change.

Therefore, those that try to sell you an atomic clock (such as rubidium or cesium clocks), are going to charge you a lot of money, and not do a thing to improve your audio!

What one may need is for various gears to clock together. Foe example, if you have 2 chassis of AD's and you want to use them simultaneously, you may need to lock them together. If you do not, and they 2 chassis are just slightly off, after say an hour, the difference in times can accumulate to be way too big. So we may need to lock gear together, but that does not make the absolute time is so important.

You would not care if an hour performance was slowed down by say 10msec, but you sure do not want to mix 2 tracks that are time a aligned at the start, but are off by 10msec an hour later...

What IS IMPORTANT is jitter, and that is a "sample by sample" problem. Say one sample is early (relative to where it should be) by 1 nsec. By the time it happened, it is too late to do anything about it. In fact, at about 8 inches of wire (or trace a way) you are already 1nsec "behind the time". And if you try to control jitter for too far - send a clean clock a long distance, you will pick up a lot more jitter in that transmission path, then you started with...

Regards
Dan Lavry

&

If the goal is to capture the analog signal precisely with an AD, and to reproduce it precisely with a DA, then less jitter is better. Random jitter increases noise. Random jitter generates harmonics, some of that energy is inharmonic. Then there is jitter that is not random, such as noise pickup from radio transmission, power lines or other environmental disturbance in the clock cables. There is also a cable termination issue (tolerance of cable impedance and termination resistance) which causes reflections on the clock cable. Then there are issues of different grounding between chassis... Then there is the clock recovery circuitry (PLL or alike)...
All that is objective.

The claim that a clock can help an AD is bogus. The clock sends a signal to the AD, but it does not receive a signal from the AD. This is a one way communication. What kind of a clock can improve the following AD's without any knowledge of how they operate?

1. AD with a lot of power line induced jitter.
2. AD with little power line induced jitter.
3. AD with a lot random jitter due to circuit analog noise
4. AD with some 30KHz jitter due to some switching supply
5. AD with jitter due to radio station.
1. AD with jitter due to the digital audio data signal.
1. AD with near perfect timing (almost no jitter).

Can a clock box that does not know what is at the other end of the cable can not send a "customized signal" for all the above cases. What happens is you turn off the AD? What kind of "magic signal" will the clock send?

The claim that an external clock can improve an AD is analogous to a doctor that can may patients with different illness, without ever seeing them or hearing from them. Again, the clock box sends the same signal to whatever you connect to it. There is no "magic" in that signal. It is just a simple clock 0,1,0,1,0,1.... And the better the repetition is the better the clock!

The clock should do one and only one thing - send a clock signal "train" where the time between is as equal as possible (minimal jitter), at the proper frequency.
This is easiest to do with internal crystal next to the AD. It is more difficult to do when the clock is in another box, and one needs to add many obstacles on the way (cable driver, cable, receiver, clock recovery circuits...).

My statements are objective. If the idea is to keep as much of the music un altered, and then jitter is you enemy. If you are for transparency, then less jitter is better.

But I can not argue with tastes, likes or dislikes. Personally, I prefer the conversion to be transparent. I do not want my amplifier to do EQ, I do not want my speaker to do compression... I do not want my conversion to yield an "edge" that was not there. One can use a EQ box for EQ, and a compressor box to do compression.

Hearing a difference is easy. A lot of things in the audio chain may sounds different to a good ear in a fine listening room. The fact is - more jitter is going backwards.
It does not take much jitter to limit the performance of a 20 bits system to 16 bits or less. I do not see anyone advocating going back to low bits...

Lets set the goal as - the AD should convert analog signal to digital with minimal
musical alteration. The idea is to take the music and convert it to "numbers" and later to convert it back to a signal, without any alterations.

If you want a different goal, that is fine. For example, one can choose to use a tube amp to alter the sound, one can alter it with EQ, reverb or what not. Such alterations are PREDICTABLE. You can state that you like what the tube amp does to your music. You can set the EQ to boost the bass of all the music.

But much of the jitter "alterations" are NOT EVEN PREDICTABLE. It varies with the music, moment by moment.

It is always difficult to present technical facts to people with less background in science or technology. It is impossible to counter arguments about what one likes or dislikes. Most often, those that made up their mind, and bought gear, tend to cling to thier opinions, especially when there is a lot of advertizing by clock makers about how external clocks improve sound of AD's.

Regards
Dan Lavry


ns

Last edited by nightscope; 28th July 2015 at 05:04 AM..
Old 28th July 2015
  #23
Gear Nut
 

Great post, nightscope!

Quote:
Originally Posted by Dan Lavry
It is always difficult to present technical facts to people with less background in science or technology. It is impossible to counter arguments about what one likes or dislikes. Most often, those that made up their mind, and bought gear, tend to cling to thier opinions
This is signature worthy!

Can someone add this to the mastering forum sticky? :P
Old 28th July 2015
  #24
Lives for gear
 

Quote:
Originally Posted by musicus View Post
Well this is depressing.

I have a rom workstation keyboard that has spdif digital audio out. My audio interface has an spdif in. "Excellent!", says I - I can connect the two and have an absolutely perfect digital transfer of the signal from the keyboard into my DAW. No need to go D/A then A/D. I will get an exact copy of the rom waveform in my DAW.

But apparently it's just a dream. One of them has to be master, the other slave. Which, apparently, means my perfect transfer is going to have additional jitter introduced into it??

I suppose one could ask if this additional jitter adds more or less loss of fidelity to the original than the a/d-d/a process.
The transfer will not introduce jitter, as you note in a later post, it's digital, bit for bit accurate.

Jitter is actually relatively unimportant when it comes to digital connections, it has to be pretty awful (in electronic terms) to cause any issues, because it has to throw things so far out of wack that a one gets interpreted as a zero.

Where the jitter matters is at the points of conversions from and to analogue (in this particular case just to analogue, since your source is digital).

So it only matters if you have an analogue stage.

So, let's say you wanted to record your synth into your DAW, run some EQ on it in the DAW, then output it through an analogue compressor, then back into the DAW.

For the absolute best quality, what you should do is set it as the master, then record it into the DAW with the SPDIF connection (which is acting as the master). Then set your ADC as the master and do the analogue processing.

But to be honest, if all the components are decent quality, we should be talking a gnat's fart in a hurricane difference. People stress so much about these issues with modern gear when the differences are typically less than you'd have got switching between two supposedly identical units of classic gear used on your favourite albums.

My suggestion is, be aware of it, but don't worry about it unless something actually sounds wrong.
Old 28th July 2015
  #25
Quote:
Originally Posted by Jon Hodgson View Post
The transfer will not introduce jitter, as you note in a later post, it's digital, bit for bit accurate.

Jitter is actually relatively unimportant when it comes to digital connections, it has to be pretty awful (in electronic terms) to cause any issues, because it has to throw things so far out of wack that a one gets interpreted as a zero.

Where the jitter matters is at the points of conversions from and to analogue (in this particular case just to analogue, since your source is digital).

So it only matters if you have an analogue stage.

So, let's say you wanted to record your synth into your DAW, run some EQ on it in the DAW, then output it through an analogue compressor, then back into the DAW.

For the absolute best quality, what you should do is set it as the master, then record it into the DAW with the SPDIF connection (which is acting as the master). Then set your ADC as the master and do the analogue processing.

But to be honest, if all the components are decent quality, we should be talking a gnat's fart in a hurricane difference. People stress so much about these issues with modern gear when the differences are typically less than you'd have got switching between two supposedly identical units of classic gear used on your favourite albums.

My suggestion is, be aware of it, but don't worry about it unless something actually sounds wrong.
Thanks to Jon for additional info, clarification, and good, practical advice.
Old 28th July 2015
  #26
Lives for gear
 

For those new to this topic, current rule of thumb is to use your main A to D converter unit as master clock for use with multiple devices. Stay away from "daisey-chaining" wordclock devices (in one device and then out to the next) if possible instead use a "T" connector setup (plenty of threads on how to do that here via search).

As for the actual differences between a "T" connector setup from a single wordclock out and doing that same via multiple wordclock outs (distribution unit) I'm guessing you might have some addition isolation but in some units they might be wired like your house outlets, in fact equal to using "T" connectors (experts chime in)?

Given how easy it is to try out your available clocking configurations just invest some experimentation time. Main A to D converter as master sounded best in my 7 device "T" connector setup (4 converter units - 80 channels of conversion / 3 interface PCI cards).

Last edited by Bassmankr; 28th July 2015 at 10:22 PM..
Old 28th July 2015
  #27
Lives for gear
Ok OP. What I am about to say is going throw the purely technical/statistical thinkers into an outrage, because they can't actually reason without their path of reasoning being approved by some authority figure (Which isn't a always a bad thing, but in the case of your own personal matters and decisions, it is), but here goes.

The best analogy to explain why jitter and clock specifications matter, even though they are statistically insignificant, is static in a television signal.

There are millions of pixels on a tv screen, changing color approximately 30 times per second. That's at the very least 30 million units of statistic per second. Now if 30 out of that 30 million pixels is late or early in changing color every second, what happens? A random 30 of the pixels at any given second doesn't belong in the image on the screen. Now you've got one wrong pixel jumping around on every frame. Statistically that's a 0.0000001% error rate. That's a far better specification than any jitter rate on a clock, and would be considered insignificant by any trained chimp. What do you perceive when you are watching that screen? The answer, is faint yet noticeably annoying background noise. Things like this are qualitative not quantitative. The only affect our perception and measurement capabilities in subjective ways. We perceive them as intangible qualities, not specifically quantifiable as a part, but noticeable in the feeling, the experience, as a whole. Measurement is as much an art form as it is a science, because our tools require skill to operate.

To get back to the topic at hand, the only real reason to use an external clock is if you notice synchronization problems between your devices. That means anything from misalignment to clicks and pops to distortion and noise. Using an external clock on one device is only going to improve it if the internal clock is of very poor performance. Usually high-end devices are designed around a clock's performance and sound best with that clock, even if its specifications are not the best you've ever seen. Usually.

Last edited by psykostx; 28th July 2015 at 10:53 PM..
Old 29th July 2015
  #28
Lives for gear
Quote:
Originally Posted by Jon Hodgson View Post
The transfer will not introduce jitter, as you note in a later post, it's digital, bit for bit accurate.
That's what I originally thought, and makes the most sense to me. And it's the answer I like best so I'm going to go with that. Thanks.
Old 29th July 2015
  #29
Quote:
Originally Posted by Bassmankr View Post
For those new to this topic, current rule of thumb is to use your main A to D converter unit as master clock for use with multiple devices. Stay away from "daisey-chaining" wordclock devices (in one device and then out to the next) if possible instead use a "T" connector setup (plenty of threads on how to do that here via search).

As for the actual differences between a "T" connector setup from a single wordclock out and doing that same via multiple wordclock outs (distribution unit) I'm guessing you might have some addition isolation but in some units they might be wired like your house outlets, in fact equal to using "T" connectors (experts chime in)?

Given how easy it is to try out your available clocking configurations just invest some experimentation time. Main A to D converter as master sounded best in my 7 device "T" connector setup (4 converter units - 80 channels of conversion / 3 interface PCI cards).
Wait, I've been reading (and so they say) that using "T" connections on word clock are actually worse than daisy-chaining. And that using a master distribution unit that has 'multiple outputs' to each piece of gear to be clocked is best when needing to use an external clock, no?

I use multiple PC's, each with their own audio/interfaces, some PC's have multiple interfaces. I'm only sending coaxial digital audio between machines (when needed) so the digital connections aren't a full-time thing. However when I am sending digital audio among machines I want it to work the best it can... although I've not had any problems that I can tell.

What I've been especially wondering about for my scenario is, what about the PC's that have multiple interfaces in them? How would it be best to distribute word clock? Even if I had a word clock generator/distributor with 'multiple' outputs, would it be a good thing to send say, the originating master word clock device, to each PC's interface, then any PC's with a 2nd interface daisy-chain that over. Basically splitting off like a tree with branches.
Old 29th July 2015
  #30
Lives for gear
+1

Quote:
Originally Posted by EastWest Lurker View Post
In a White Paper, Dan Lavry, who designs some of the best converters ut there, say an internal crystal will always have the least jitter unless it is very poorly designed, and that most are pretty good. So if you use an external clock to a single interface you are introducing more jitter and unless for some reason you prefer that sound, which I guess is possible, you are making things worse. External clocks obviously are fine for clocking multiple interfaces.
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