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Master Clocks...Snake Oil?

solderdude

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#2
A master clock is almost obligatory in a studio where one wants all digital equipment to sample at the same time.

Some audiophiles swear by them and claim miracles.
When I would 'upgrade' my $100k + home system and bought a very expensive clock my brain would make damn sure I hear positive things.

Whether it would REALLY make an audible difference is debatable.... acc. to some.

It would be really sad though if someone bought a very expensive DAC with an external clock input only to find out that spending multi-thousands of $ for a few $ worth of DAC chips still couldn't buy one at least a decent clock and would have to fork out another $8k just to add yet another clock that the device would be slaved to.

But... there is a market for it.
 

amirm

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#4
The best clock is one that is sitting right next to the DAC chip. One in an external box cannot do that. In addition, we don't need accuracy in clocks. Audio playing .01% slower or faster doesn't matter (ask all the analog LP lovers with such variations). So you don't need an accurate reference clock. You need a clean one and the cleanest one will have no cable, another power supply to create ground loops, etc.

So definitely pass on such things.
 

RayDunzl

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#5
I found this Reference Master Clock that's $7,995

Master clocks have their place.

These were far more expensive.

I worked on Central Office Phone Switches 1983-1995 or so. A big one would cover a basketball court. A bigger one would occupy several floors of a downtown building.

It had a Master Clock module, providing clock (probably) to (eventually, including repeaters/distributors) every card in the local system.

Each analog phone line would be digitized (ADC) at an 8kHz sample rate. The active lines in a Line Frame would be multiplexed (time slots) on to a cable going to one of the Switching Frames.

The time-multiplexed samples were then space-multiplexed by switch (changing their time slot assignments) and sent out on different cables, again time multiplexed and sent to another Line Frame to be demultiplexed to the Line Card handling the other phone in the conversation, or, if the call was to terminate externally to the office, to a time slot on a Trunk going down the road.

A small office would be TST - time space time, a larger facility would be TSST adding another space switching step.

The voice calls were - regardless of the distance, synchronous - one sample in, one sample switched, one sample delivered to the destination line card's DAC and cable to the phone.

Since the base 8kHz rate had to match among different Offices, that Master Clock was really a slave to the clock rate on a selected Trunk line from another office. Ever make a call and hear tick-tick-tick as the time slots slipped due to missing sync somewhere?

It could free-run if the distant clock disappeared, so it had to be stable to maintain reasonable sync with other offices during such an outage.

Later, Sonet (Synchronous Optical Network) came into being, along with the need for the whole network of machines to be synced for the signalling (SS7) and time multiplexed voice samples got to the destination on time and in order.

Then that all blew up and is likely replaced with VOIP, voice mingled with Internet Traffic, no longer single synchronous voice samples delivered to a destination, but bundles of your voice samples delivered to a destination to be resampled and ASRC'd at the endpoint.


Would such an upgrade really make an audible difference?

At home, I don't think about it. Stuff works and doesn't squeal or tick so it must be working just fine.

The Ceiling Fan, somebody moving in the room, even just waving your hand creates more disturbance in the Audio delivered to your ears than what is seen from any imperfections in the electronic's clock, in my view


.
 

digitalfrost

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#6
I am using multiple DACs for my stereo output (semi-active system) and I rely on the clock in my RME soundcard to keep all the DACs in sync via SPDIF. If you have multiple digital devices, especially while recording played back content, a good master clock is an absolutely necessity.

If I make any audio measurements through two separate async USB devices, I get huge offsets in time between channels, even when measuring one directly after the other.
 

j_j

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#7
Well, if you're doing multichannel you really want exact sample lock on properly created material.

On the other hand, 7K for that seems a touch egregious. Like somebody above pointed out, it's not a new problem needing a solution.
 

j_j

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#8
The best clock is one that is sitting right next to the DAC chip. One in an external box cannot do that. In addition, we don't need accuracy in clocks. Audio playing .01% slower or faster doesn't matter (ask all the analog LP lovers with such variations). So you don't need an accurate reference clock. You need a clean one and the cleanest one will have no cable, another power supply to create ground loops, etc.

So definitely pass on such things.
Unless you have multiple DAC's playing back multichannel. Then sample lock is mandatory. A small constant error, though, remains meaningless.
 

andymok

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#9
Unless you have multiple DAC's playing back multichannel. Then sample lock is mandatory. A small constant error, though, remains meaningless.
Constant error could cause issues in time alignment like phase issue, I suppose?
 

amirm

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#10
Constant error could cause issues in time alignment like phase issue, I suppose?
It is more than phase. They will drift seconds or minutes out of sync over time.
 

Rja4000

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#11
The best clock is one that is sitting right next to the DAC chip. One in an external box cannot do that. In addition, we don't need accuracy in clocks. Audio playing .01% slower or faster doesn't matter (ask all the analog LP lovers with such variations). So you don't need an accurate reference clock. You need a clean one and the cleanest one will have no cable, another power supply to create ground loops, etc.

So definitely pass on such things.
For a simple setup, that's sure.
In a recording studio or large live PA system, that's another story.
In such system, nowadays, the clock is distributed by the Audio Network (Dante or other).
 

j_j

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#12
For a simple setup, that's sure.
In a recording studio or large live PA system, that's another story.
In such system, nowadays, the clock is distributed by the Audio Network (Dante or other).

And the clock sync must be very much sub-microsecond between channels, please, as well as free of any notable jitter.
 

Veri

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#15
Wow, very very interesting. Thanks for sharing! I love the conclusion

Overall, it should be clear from these tests that employing an external master clock cannot and will not improve the sound quality of a digital audio system. It might change it, and subjectively that change might be preferred, but it won't change things for the better in any technical sense. A‑D conversion performance will not improve: the best that can be hoped for is that the A‑D conversion won't become significantly degraded. In most cases, the technical performance will actually become worse, albeit only marginally so.

Which makes the subjective reviews of audiophile clocks like the Cybershaft/Mutec/etc on head-fi, audiphilestyle and the likes simply absurd. They just about always feel the sound gets slightly better/cleaner when using such an external pricy clock! One might almost suspect a huge expectation bias creeping in, clouding their judgement.... :)
 

Krunok

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#16
I think this is the most important part:

However, in more elaborate and expansive systems, where there are several A‑Ds and lots of other digital outboard, it's often more convenient and practical to have a centralised master clock source, and to distribute clocks from that to all of the other devices, all of which are configured as slaves. All master clock units provide numerous word clock outputs, and often several AES11 clocks too (AES11 is basically a silent AES3 signal, intended specifically for clocking purposes). In this kind of system, though, it would be worth ensuring that the A‑D converters all work well when operating on external clocks, to maximise their audio quality.

The only situation where a dedicated master clock unit is truly essential is in systems that have to work with, or alongside, video, such as in music-for-picture and audio‑for‑video post‑production applications.

I used to work for national broadcast TV and master clock was regularly used in studios to synchronize multiple devices but I really see no use for master clock in home environment.
 
Last edited:

Krunok

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#17
Well, if you're doing multichannel you really want exact sample lock on properly created material.
True. But if you're doing multichannel you'll probably have a multichannel DAC with single clock and not a bunch of stereo DACs.
 

eliash

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#19
Master clocks have their place.

These were far more expensive.

I worked on Central Office Phone Switches 1983-1995 or so. A big one would cover a basketball court. A bigger one would occupy several floors of a downtown building.

It had a Master Clock module, providing clock (probably) to (eventually, including repeaters/distributors) every card in the local system.

Each analog phone line would be digitized (ADC) at an 8kHz sample rate. The active lines in a Line Frame would be multiplexed (time slots) on to a cable going to one of the Switching Frames.

The time-multiplexed samples were then space-multiplexed by switch (changing their time slot assignments) and sent out on different cables, again time multiplexed and sent to another Line Frame to be demultiplexed to the Line Card handling the other phone in the conversation, or, if the call was to terminate externally to the office, to a time slot on a Trunk going down the road.

A small office would be TST - time space time, a larger facility would be TSST adding another space switching step.

The voice calls were - regardless of the distance, synchronous - one sample in, one sample switched, one sample delivered to the destination line card's DAC and cable to the phone.

Since the base 8kHz rate had to match among different Offices, that Master Clock was really a slave to the clock rate on a selected Trunk line from another office. Ever make a call and hear tick-tick-tick as the time slots slipped due to missing sync somewhere?

It could free-run if the distant clock disappeared, so it had to be stable to maintain reasonable sync with other offices during such an outage.

Later, Sonet (Synchronous Optical Network) came into being, along with the need for the whole network of machines to be synced for the signalling (SS7) and time multiplexed voice samples got to the destination on time and in order.

Then that all blew up and is likely replaced with VOIP, voice mingled with Internet Traffic, no longer single synchronous voice samples delivered to a destination, but bundles of your voice samples delivered to a destination to be resampled and ASRC'd at the endpoint.





At home, I don't think about it. Stuff works and doesn't squeal or tick so it must be working just fine.

The Ceiling Fan, somebody moving in the room, even just waving your hand creates more disturbance in the Audio delivered to your ears than what is seen from any imperfections in the electronic's clock, in my view


.
Boca-ey?
 

RayDunzl

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#20
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