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Old 19th April 2007, 05:13 PM   #1
JZatopa is offline JZatopa  United States
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Default The ultimate clock!!!

So who is going to be first with trying to mod their cd/dvd player to use a clock like this?

http://news.harmony-central.com/Newp...hrone-10M.html
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Old 20th April 2007, 02:00 AM   #2
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I like junk like:
Quote:
Based on over 15 years of clocking research, from skilled engineers renowned for their accomplishments in the field.
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Old 20th April 2007, 08:00 AM   #3
Fin is offline Fin
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This suggests that they need some lessons regarding jitter:-

Quote:
With impressive stability of 0.03 ppB (parts per billion), the Isochrone 10M has a practically immeasurable jitter, while the Rubidium technology ensures the most stable and accurate clock reference possible.
Accuracy has got nothing to do with jitter. Jitter is all about precision.
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Old 22nd April 2007, 11:09 PM   #4
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"Whereas an average crystal oscillator running free at 98Khz would lose one audio sample a second, "

OH NO! MY PRECIOUS SAMPLES! This is hilarious.
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Old 22nd April 2007, 11:18 PM   #5
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Quote:
Originally posted by Fin

Accuracy has got nothing to do with jitter. Jitter is all about precision.
I imagine it would be hard to be precise if one is not accurate.
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Old 22nd April 2007, 11:30 PM   #6
phn is offline phn  Sweden
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Quote:
Originally posted by rfbrw


I imagine it would be hard to be precise if one is not accurate.
Cracked me up.
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Old 23rd April 2007, 12:57 AM   #7
Fin is offline Fin
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Quote:
Originally posted by rfbrw


I imagine it would be hard to be precise if one is not accurate.

Not hard at all. Accuracy and precission are two entirely different things.

Accuracy is a measure of how close a result (or average of a series of results) is to the true value or desired value.

Precission is a measure of how close a series of results are grouped together.

Imagine throwing darts at a dart board while aiming for the Bulls Eye. If all of the darts end up around the circumference of the dart board with none of them landing close to together........this is not very precise.....but the average position might be quite close to the Bulls Eye and be deemed to be accurate. In a second attempt at throwing the darts at the board - all of the darts might land in one neat group in the doubble 20 position. This would be very precise...but not accurate.

So - with clocks - you could have one that has a very accurate average output being only a few ppm or ppb from the specified value. However, the timing of the output from one instant to the next could still be varying considerably and therefore not very consistant. The accuracy would be good but the precision would be bad.

It is my understanding that the accuracy is not so important as long as it is within Red Book specs.....but the precission (low jitter)is most important.
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Old 23rd April 2007, 11:04 AM   #8
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I have two of these. One for DAC and one for servo clock

Brent
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Old 23rd April 2007, 11:30 PM   #9
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Quote from Guido Tent:

Techtalk

I’d like to share with you some basics on jitter. Jitter
are short term deviations from something that is supposed to show constant performance. Consider a normal watch that ticks every second. If the ticks are not evenly spaced we have a jittery clock. Usually this is no problem, as long as the long-term stability is OK you’ll be in time for your next appointment. However,
there are occasions that clock-jitter is of utmost importance, for example a 1 00m race. Differences are in the order of 0.01 s so each second should precisely be second!.

Redbook

The same holds for audio! It is of no importance whether the clock is slightly off its’ absolute frequency, specified in ppm’s (parts per million). According to the redbook CD standard, limits are +/-100ppm. A single 440Hz tone then could only deviate +/- 0.044Hz- inaudible.
It now becomes clear that specifications like 2ppm accuracy do not add to sound quality. A TCXO is such clock that achieves low ppm values, as it is very constant over long time. Fine to have on board of an accurate frequency counter, but no use for audio.

Short term

The short-term stability is important! Cycle to cycle deviations, or cycle to 100.000th cycle. If you look at the spectral content of such signal, it should look like a single frequency, with the noise floor as low as possible
(as all periods T are equally long, this translates in a single frequency 1/T). Practical clocks do not show that very narrow single frequency, but a bit wider spectrum, rapidly decreasing at 10 to 100Hz from the central frequency. A well-known clock supplier tried to convince us by showing this graph:
What we actually see is the performance of the analysers’ video filter, namely 1 kHz. Good clock spectra are well withing this window. The only clock performance we can deduce from this measurement was the one that didn’t count for audio: It meets the redbook spec. It does not meet the manufacturers own spec of 5ppm though .........

Read the whole article here.
http://www.tentlabs.com/News/assets/...ber%202006.pdf
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Old 24th April 2007, 02:18 AM   #10
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Thank you Menno. This is the point I was trying to make - but Guido does it better.


Quote:
Originally posted by Menno Keizer
Quote from Guido Tent:

It is of no importance whether the clock is slightly off its’ absolute frequency, specified in ppm’s (parts per million). According to the redbook CD standard, limits are +/-100ppm. A single 440Hz tone then could only deviate +/- 0.044Hz- inaudible.
It now becomes clear that specifications like 2ppm accuracy do not add to sound quality. A TCXO is such clock that achieves low ppm values, as it is very constant over long time. Fine to have on board of an accurate frequency counter, but no use for audio.
Accuracy is not relevant to jitter.


Quote:
Originally posted by Menno Keizer
Quote from Guido Tent:

The short-term stability is important! Cycle to cycle deviations, or cycle to 100.000th cycle. If you look at the spectral content of such signal, it should look like a single frequency, with the noise floor as low as possible (as all periods T are equally long, this translates in a single frequency 1/T). Practical clocks do not show that very narrow single frequency, but a bit wider spectrum, rapidly decreasing at 10 to 100Hz from the central frequency.
Precision is most important.


From a scientific, analytical and statistical point of view - it is obviously desirable to have good accuracy with a high level of precision. However, Accuracy and Precision are not intrinsically linked. As mentioned previously, a series of measurements (or the time interval between pulses from a clock) can be very tightly grouped with almost identical values and a low standard deviation. This indicates a high level of precision and good reproducibility. This is what the best clocks are trying to achieve and results in lower jitter.

Despite this high level of precision, it tells us nothing about the accuracy of the measurement or result (how close this tightly grouped series of measurements is to the "true" or specified value). Fortunately - for audio - this accuracy is not too important.

So - to restate my original point.....it is possible to have:

1. Good accuracy with good precision.

2. Good accuracy with poor precision.

3. Poor accuracy with good precision.

4. Poor accuracy with poor precision.


I hope this helps to clear up any confusion between Accuracy and Precision.
.........................................
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