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Re: Quality of CoreAudio SRC
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Re: Quality of CoreAudio SRC


  • Subject: Re: Quality of CoreAudio SRC
  • From: Brian Willoughby <email@hidden>
  • Date: Fri, 1 Feb 2008 07:28:31 -0800

Hi Chris,

I think you're missing a couple of things (or perhaps I am).

First, latency is an artifact of correcting the problems of externally-clocked DACs, consequent to a data push model. The audio industry is too entrenched in the established, but unfortunate, standards of AES/EBU and SPDIF (and I do not believe that USB improves upon them significantly).

When you say "clocked by the computer itself" - this is only possible when the audio interface is inside the computer, in which case you really mean the the audio interface DAC is clocking itself, not "the computer." With a proper DMA design, the same clock would drive both the DAC and the data flow, thus alleviating the need for locking to some external clock. When you mention limitations, I assume you're talking about the noise inherent to placing analog audio in a computer chassis.

Second, I'm not sure what you mean when you claim that the LavryBlack can clock to 'crystal' - The DA10 only offers modes which are locked to an external clock. It cannot operate on an internal clock because it has no data source under it's control. All possible transports are external, and are data push designs, thus the need for external lock. Thankfully, the LavryBlack offers three lock modes, but all are compromises compared to the capabilities of a (theoretical) self- clocked DAC with bidirectional control over sample data flow, the only way to make a data pull model possible.

i.e. The LavryBlack IS NOT a local, crystal clock.

If you follow my high-level circuit system descriptions, then perhaps you understand why I ask for a different design. There is no reason, other than historical, for a playback/mixing/mastering DAC to have the limitations that you experience. The best excuse I have heard is the expense of developing a proper FireWire bus master with audio. Given the typical prices of DAC units in Pro Tools studios these days, I don't buy that excuse for one minute.

I think I will be looking into the purchase of Metric Halo and/or RME FireFace audio interfaces. I don't think the audiophile industry, per se, is prepared to outdo these companies' offerings. Audiophiles seem locked (if you'll pardon the pun) into using jitter removal on external clocks, and they're willing to pay through the nose for this over-engineered solution to a pervasive, historical design flaw.

Again, forgive me for the tangent. I have been pursuing this technology for years, and it's hard to find the knowledge base anywhere else! In my thinking, this quest is quite related to CoreAudio, because CoreAudio has finally embraced the proper pull model for sample data flow that is needed for a truly audiophile DAC design.

Brian Willoughby
Sound Consulting


On Jan 31, 2008, at 23:02, Chris Johnson wrote: On Feb 1, 2008, at 12:52 AM, Brian Willoughby wrote:

I am surprised that Benchmark chose USB, since that interface requires jitter removal. No matter how good your jitter removal, it's never as good as a local, crystal clock. ...



According to Dan Lavry, FireWire is too expensive to develop for, although with his prices I don't see how it would be much different.

Sorry to talk near-audiophile language here, but this list combines a unique collection of software engineers and FireWire designers (Metric Halo and maybe even MOTU and RME). I have been trying to identify the ultimate audio interface for Mac, along with the correct software to drive it. I am up to the task of developing the software, and even drivers if need be, but the research on the possibilities for hardware is still ongoing.


I would imagine it has a lot to do with your requirements for latency. If you need low latency, it's hard to beat stuff clocked within the computer itself, but that will have its own limitations.


Funny that you should mention Lavry, because I use one of his Lavry Blacks for most of my monitoring of serious work. If it was USB I can't see how it would be much different, because Lavry's reclocking is so comprehensive that it incurs enormous latency. I cannot track through this unit (even on 'wide' clock acceptance, oddly enough!) but I haven't had any complaints about its audiophile qualities- when clocking it to 'crystal', the sound is seriously unjittery.

Of course, that IS a local, crystal clock- hence the name. So I guess your point stands :)

But again- I absolutely cannot track through the amount of latency this DAC incurs, on any setting. It's a playback/mixing/mastering DAC.


Chris Johnson airwindows

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