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GPS audio master clock

175.45.6.61
Posted on July 25, 2012 at 03:16:00
eduardoo
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 I came across these couple of interesting audio master clocks from Japan, both of which derived their timing from GPS signals.

http://www.ippinkan.co.jp/airbow/product/others/gps10mh.html
http://www.ippinkan.com/infranoise_gps777.htm

They seem pretty affordable(?) for the accuracy that they claim over similarly priced products (they go for about US$2-3k. While I understand that GPS clock signals would probably be a lot more accurate than most (save for those Rubidium ones), would the bottle neck be in the receiver that needs to convert the received signal back to a clock signal (which may be pll based)? Also, would a clock like this need to be synced to a particular satellite or does anything go? The reason I asked this last question is that I don't live in Japan, and if the thing only works with some signal that is only present there, it would be useless.

I am quite interested to know what the tech savvy inmates think about this implementation. If it is good, I might pick one up next time I am in Japan and use it with my Esoteric K-03 (which is said to have an accuracy of 0.5ppm).

Thanks.

 

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get your own atomic clock chip for half that price, posted on July 25, 2012 at 06:23:38
kh6idf
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 see link below:


 

RE: GPS audio master clock, posted on July 25, 2012 at 06:23:53
Tony Lauck
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 Except for a few (rare) broadcast applications there is absolutely no benefit to using a GPS clock or atomic clock for audio. There is no need for playback to take place at the exactly correct rate and pitch, as it wasn't recorded that way and a tolerance of 0.1% is more than adequate.

The devices are made for laboratory purposes and output 10 MHz. This requires using a frequency synthesizer (including a phase lock loop) to generate the clocks commonly needed for audio. This process will unavoidably add jitter compared to a local free running clock, and hence sound quality will be degraded through use of these clocks.

About the only exception might be streaming applications for continuous operation where low latency is required, such as broadcast audio of sports events. If the streaming source and the receivers were both locked to the same time base then it would be possible to avoid an occasional buffer glitch every few hours. In practice, there would still be glitches caused by Internet glitches, so this "improvement" might not even be noticed.


Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar

 

RE: get your own atomic clock chip for half that price, posted on July 25, 2012 at 12:41:14
pictureguy
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 Half a microsecond / day!
And suitable for embedded devices / applications.

Now, how does that accuracy / repeatability and precision compare with the range of jitter specs measured on current consumer digital devices?
Is CD or DAC jitter in PPM or ???

Using the broadcast WWV / WWVH signal in a home situation is generally impractical, though I know of the in-home 'atomic clocks' with built in receivers. If you live in the wrong place, using WWV becomes less than practical.
WWV is what? 10KW or maybe 25KW? Even with a good SW receiver I am sometimes not able to get a good, stable signal at any frequency from 5Mhz to 20Mhz. I'm not sure about lower fequencies.
I've even logged WWVH from the Hawaiian islands....You can sometimes hear it during the planned downtime of WWV which still comes from Ft.Collins, Colorado.


Too much is never enough

 

RE: get your own atomic clock chip for half that price, posted on July 26, 2012 at 19:49:41
eduardoo
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 Nice, but I guess once the rest of the electronics are put together (to make it compatible as an external audio master clock), it would probably cost a small fortune.

 

RE: GPS audio master clock, posted on July 26, 2012 at 19:51:48
eduardoo
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 Thanks, Tony, for the informative post.

I would think that the frequency synthesizer would take away the benefits of the accuracy upstream, too. Interesting idea anyway.

 

RE: GPS audio master clock, posted on July 26, 2012 at 19:57:42
Tony Lauck
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 No, a correctly implemented frequency synthesizer will preserve the long term frequency (timing accuracy) from the GPS or atomic clock. There will be short term variations, but these will get cancelled out. So if you are using one of these puppies to run a clock, it will keep constant time, until the next leap second. :-)


Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar

 

RE: GPS audio master clock, posted on July 26, 2012 at 22:57:25
eduardoo
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Joined: August 14, 2002
 If it can keep the accuracy of the GPS, wouldn't it be possibly be better than most internal clocks of CD players (although my Esoteric already claims pretty high accuracy at +/-0.5ppm)?

 

RE: GPS audio master clock, posted on July 27, 2012 at 06:19:30
Tony Lauck
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Posts: 13629
Location: Vermont
Joined: November 12, 2007
 These specs say nothing about jitter. One can have accuracy without low jitter. It's a case of accuracy without necessarily having precision.


Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar

 

Clock specs, posted on July 27, 2012 at 14:18:10
John Swenson
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 There are a number of specs for clocks, many of which are unimportant for digital audio. The most import spec is jitter, or phase noise. Getting a phase noise plot is better rather than just a ps number, the spectrum of the jitter IS important.

Other paramters are initial accuracy, long term accuracy, and temperature coefficient.

Initial accuracy is how close is the actual frequency when you get it compared to the frequency marked on the case. Usually speced in PPM (parts per million). Thus for a 10Mhz clock 1 PPM would be up to 10Hz off. Very high accuracy here is usually completely irrelevent to sound quality. Very bad accuracy can mean that a PLL may not lock, but that usually mean it has to be 200 PPM or more off. Almost all crystal oscillators are much better than that.

Long term accuracy defines how the frequency changes over time (usually PPM per year or a graph). Most clocks will slowly change frequency over time. A clock might have an initial accuracy of 20 PPM but after 10 years it might have drifted by 150 PPM. Again only a problem if it gets so far out of range that other devices can not lock on.

Temperature coefficient is how the frequency changes with temperature. Frequently this is in PPM per degree C. Of all the "accuracy" parameters this is the one that can most easily cause problems. Many oscillators have numbers of 20PPM or higher per degree C. Think about what this means, a 10 degree C change in temperature means a 200PPM change in frequency! A 10 degree change in temp is not that big, you can easily get that during "warm up" after you turn on a box. This is most important for a "transport", ie something that feeds a signal to some other box that has to lock on to it. It is not related to "sound quality", but if the frequency gets too far off the DAC might not be able to lock on. A down side is that the circuitry that adds the temperature stability can actually increase jitter.

Some manufacturers have started using temperature compensated clocks to get around these issues, but the marketing literature makes a big deal about the 1PPM tempco as if this makes the sound better, but what it really does is guarantee that a DAC can still lock to the signal no matter how hot or cold it gets in your living room. A strange aspect of this is that most manufacturers that boast about low tempco of their clocks do so for their DACs where this is almost irrelevant. Transports are what need it.

So when a manufacturer starts boasting about a PPM number of their clock, make sure you know which paramter it is, the only one with much relevance is tempco (or temperature stability, same thing), and even then not much importance for a DAC.

Now it may very well be true that a certain expensive oscillator with a low tempco MIGHT have low jitter, but there is no guarantee. You can eaisly find clocks with very low jitter that do not have very low tempco, and you can find clocks with low tempco that have lousy jitter.

I'm sorry for making this so long, but this is a subject that really bugs me, manufacturers trying to get you to buy their DAC because it has a "high accuracy clock".

John S.

 

It's actually WWVB at 60KHz long wave....., posted on July 28, 2012 at 21:33:28
AbeCollins
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 ...for typical consumer 'atomic clock' synchronization using a time code. You're unlikely to get it on most general coverage / shortwave receivers as the signal is well below the US AM broadcast band in frequency.

 

RE: It's actually WWVB at 60KHz long wave....., posted on July 29, 2012 at 08:54:51
pictureguy
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 I've never received WWVB...My LW receiver goes to only 150KHz. As it turns out, I've never gotten ANYTHING below the standard AM band.
Antenna length is daunting and normal interferrence wipes out anything that remains. I don't recall trying those frequencies when Southern California had a near-12 hour power lapse last year. At that time, normal SW reception was Epic. and electrically quiet. Too bad I couldn't power my Stereo.

The modules used in 'atomic clocks'....which I guess just update themselves every day (nite, actually, when reception is best) are sometimes removeable....so the real over achiever could use one of THOSE and probably get the same end result or better...as one of those expensive 'local' modules w/built in source.

WWV and WWVH broadcast the encoded time as well as WWVB.....And since it is the LW version which provides the time code, for 'atomic clocks', my objection to WWV / WWVH is out the window.

As a total aside, the US uses ELF or VLF to communicate with subs. The waves will go thru some depth of salt water. The transmitters take up a LOT of space, miles in most cases. Also, due to huge inefficiencies, radiated power is just a small fraction of that needed to run the operation.
Too much is never enough

 

RE: It's actually WWVB at 60KHz long wave....., posted on July 30, 2012 at 17:38:54
Tony Lauck
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 . The transmitters take up a LOT of space, miles in most cases.

HAARP deals with this.

Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar

 

RE: It's actually WWVB at 60KHz long wave....., posted on July 31, 2012 at 08:55:15
pictureguy
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 I thought the ELF / VLF antenna array was in Michigan?

The Russians have s similar program at a frequency near 60Khz.



HAARP is high frequency stuff.....10Mhz......and sounds weather related.
Too much is never enough

 

RE: Clock specs, posted on August 3, 2012 at 13:20:43
AbeCollins
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 "A down side is that the circuitry that adds the temperature stability can actually increase jitter."

Are you talking about the passive components with predictable temperature coefficients like capacitors and thermistors often used in Temperature Compensated Crystal Oscillators? Or a temperature controlled heated chamber used by Oven Controlled Crystal Oscillators?

And then there are atomic oscillators based on the natural resonant frequency of Rubidium and Cesium gas that actually 'steer' a crystal oscillator with a varactor diode.

 

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