Re: Quality of CoreAudio SRC
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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