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DACs, external clocks, and what's what

There seems to be more hype about DACs than about anything in this overhyped hobby. I'm considering a new DAC and have been dragged down this external clock rabbit hole.

It seems that lots of DAC vendors are pushing external clocks. Even high end DACs like Wadax studio player, dcs products, Master fidelity NADAC-C, etc., claim that an expensive external clock is absolutely necessary to reach peak performance. Others, such as MSB and EMM Labs-its owner, Ed Meitner, in particular, counter that the clocking function is best performed closest to the conversion so as not to introduce the inevitable issues-noise, etc., that can come with adding more cables and connectors to the process. Most importantly, they point out that the internal clock still performs the ultimate clocking function, not the external clock. According to this camp, a well designed DAC with a high quality internal clock cannot benefit from an external clock and the added box may even be a detriment in addition to a waste of money. Cynics imply its just a money grab.

I understand how external clocks can benefit professional setups where there are multiple components to consider. I have a hard time understanding the mechanism by which a simple, typical two channel dac would benefit. Both my dcs Bartok and the Studio Player are one box solutions. I've auditioned the Studio Player (no external clock) and think its really good. Also have recently heard the EMM Labs and Berkeley Reference 3P, all sound really good without an external clock.

On the other hand, these clocks are selling-even very expensive ones-and lots of folks say they hear a difference.

I'm certainly not a DAC designer. I think no one knows more about this stuff than Meitner, or the MSB folks, but this is quite confusing, at least to me. Lots of stuff in our hobby comes down to subjective preference, but this seems to be a case where one side must be right and the other is wrong. Which is which? If you think an external clock provides a substantial improvement, how so?

Just looking for insights and opinions from this esteemed group. Not trying to start a fight-just hoping to shed some light on this because its an important consideration in making buying decisions.

Thanks.

kerrybh
ted_b
66 posts
 

"... a well designed DAC with a high quality internal clock cannot benefit from an external clock ..."

"Cannot" is a strong word. A well-designed DAC featuring internal clocks (usually SC OXCO) that are galvanically isolated from noise, have their own separate low-noise power supply, and demonstrate very low phase noise, is a fairly expensive DAC. It may not deliver clock performance that approaches a Mutec REF10 SE120 external clock (6500 USD), but designed competently, it pushes what the best external clocks can improve well into the realm of diminishing returns. Conversely, relatively inexpensive DACs with external clock inputs have become fairly popular, and can often be improved to some extent with external clocks <1000 USD that offer strong phase noise performance (e.g. LHY OCK-2S). External clocks aren't limited to what can be fitted into the confines of a DAC enclosure, so there is space to improve hardware and performance ... in theory anyway.

We should note that unless the DAC has an internal PLL (phase locked loop), its clocks are engaged only when the input is via USB or a direct ethernet connection anyway. If the connection type is SPDIF, AES EBU, or I2S, we’d want to start looking at the source component (or DDC) for an external clock port. 

glennewdick's avatar
glennewdick
1,969 posts
 

 

ted_b

"We should note that unless the DAC has an internal PLL (phase locked loop), its clocks are engaged only when the input is via USB or a direct ethernet connection anyway. If the connection type is SPDIF, AES EBU, or I2S, we’d want to start looking at the source component (or DDC) for an external clock port."

I was under the impression that all modern DAC's have buffers, that then use the internal clock.  Older DAC’s without the buffers used the external clock.

ted_b
66 posts
 

I was under the impression that all modern DAC’s have buffers, that then use the internal clock.  Older DAC’s without the buffers used the external clock.

@glennewdick USB audio data is asynchronous, and is fed into a FIFO buffer in the DAC. The release of data from the DAC’s buffer is timed by the DAC’s internal clock. Open a DAC, and its clocks can usually be found on the USB transceiver board.

Data transmitted to the DAC via SPDIF/AES EBU/I2S connections differs in that it is synchronous, containing both audio and clock data from the source. The source holds the master clock, and the receiver (DAC) is the slave. As such, source clock quality is a defining influence of overall audio quality, and expensive streamers put emphasis on clock architecture for this reason. A few upmarket DACs (e.g. Gustard A/X/R-26 and later, Holo Audio May, etc.) have a PLL feature that allows the DAC to slave the source clock to its own.

Popular external DDCs (Digital-to-Digital Converter) virtually all convert USB to a synchronous format (SPDIF/AES EBU/I2S) that makes the DDC the master clock in the chain. Predictably, they also emphasize clock accuracy as a selling point.

mike_in_nc
1,250 posts
 

Some may find this pro sound take on the issue informative.

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