scott wurcer said:
I suspect the connection is somewhat tenuous. Its quite possible that reducing the clock jitter will make a DAC sound better, but only after all of the the other sources of error that are audible have been reduced enough for it to be significant. However its very possible that a $1.49 clock chip tied to the logic supply will have enough jitter and supply modulation to significantly influence the sound. However a decent bypass/filter on the right supply will probably move the significant problems somewhere else. BUT if you have a hammer (ultra low jitter) all problems are nails. . .
An example of why the obvious seems to escape many people in the trade. I have a demo board of an "ultra clock" to evaluate. I fired the sucker up and connected it to a modulation analyzer (much easier than a bunch of specialized hardware) and looked for some residual FM in its output. I got 6% modulation at 30 KHz!!! Something must be wrong. So in looking at the board there is a switching supply on it for supporting some other circuitry. And the supply seems to be modulating the ultra low jitter clock, a lot. I don't understand what happened but clearly someone didn't see the importance of keeping the noises away from the clock. Possibly they didn't detect this issue. Somehow.
That's why there is plenty of opportunity to make better audio in digital.
That's why there is plenty of opportunity to make better audio in digital.
The critical importance of the stability and quietness of the DAC's power supply is obvious. The same goes for other parts selection (like resistors and capacitors), PCB layout and all other measures relevant to audio circuits design and building.
1audio said:
Demian,
You may be interested in the test of the Benchmark DAC in the Jan 09 issue of AudioXpress. When Variac and I visited the RMAF08 last November, from talking to the Bencmark rep we already got the the idea that that Benchmark DAC was something special. AX tests seem to bear that out: one of Gary Galo's conclusion was that the Benchmark was so good in blocking incoming jitter that differences between digital interlinks and transports fade away.
Those differences of course being the results of differences in jitter that cables and transports send to the DAC, and the DAC's inablility to reduce it (to reclock it) to below audible levels. The Benchmark apparently IS able to reduce the incoming jitter to below audibility. Which makes a $30 transport sound the same as a $20.000 dCS. And ohh yes, a Benchmark goes for $1300 or less...
Jan Didden
To some up my inquiry into the DAC part of my audio system:
Provided the clock's and DAC chip's power supplies are very clean and stable – and provided all other important measures, like PCB layout, are taken:
Will a crystal oscillators having accuracy of +/- 25 ppm, Jitter RMS of 1 psec Max and phase noise of about -105 dBc/Hz at 100 Hz and -131 dBc/Hz at I KHz, costing $29.08 be the reasonable choice?
Or is there a crystal oscillator costing up to $200 with a better noise floor that will justify the extra cost in improving the sound quality?
Provided the clock's and DAC chip's power supplies are very clean and stable – and provided all other important measures, like PCB layout, are taken:
Will a crystal oscillators having accuracy of +/- 25 ppm, Jitter RMS of 1 psec Max and phase noise of about -105 dBc/Hz at 100 Hz and -131 dBc/Hz at I KHz, costing $29.08 be the reasonable choice?
Or is there a crystal oscillator costing up to $200 with a better noise floor that will justify the extra cost in improving the sound quality?
janneman said:
My attempt is to build a DAC better than the Benchmark. I believe the case will cost more than all other parts.
janneman said:
Jan,
If transports sound the same it does not mean yet that the sound quality is perfect. I have a friend who uses the latest Benchmark. He did notice one interesting effect - the sound is the best when the unit is used with 96K/24 bit feed from USB. And that is apparently the only case when the Benchmark does not resample the input. Same sound could mean the same mediocre sound, that is a problem 😀 .
Alex
john curl said:
So there you've got it from John Curl. There has been no meaningful technical development in digital audio in the past 15 years. No need to revisit a 15 year old test.
Aside from probable absent bias controls in the listening session, which was blessedly *not* called a test...
Nice of you John to deconstruct your opening comment. ;-)
janneman said:
Jan, I wish I had known you were going to be there. I live about a half hour drive from there, but usually don't go because of the high ratio of hype to substance. Last time I went was in 2006, specifically to take part in the demos and workshops that Bob Cordell and Peter Smith put on. Sorry I missed the chance to meet you guys.
There was a thread over at head-fi in which a Benchmark guy was talking about some design details of this DAC. The AD1896 ASRC chip is what gives it the jitter rejection. Someone in that thread mentioned a similar BB/TI ASRC chip. The Benchmark guy said they tested it, and its jitter rejection was not nearly as good as the AD device, apparently because of a shorter time constant in one of its internal PLL filters.
There's an interesting paper on ASRC here. I'm not up on the theory, but the long and short of it is that timing errors such as jitter are encoded into the output data. This seems to be something like FM to AM conversion. But if the clock is modulated in a sinusoidal fashion and no sidebands appear at the output, then it would appear that the encoded data errors may be randomized in some way, or maybe shifted out of band, which I think is a good thing. The paper does seem somewhat FUD-like, but it is a good read.
x-pro said:
Hi Alex,
Variac and I talked to the benchmark guy at some length, and indeed it seems that they put a lot of effort in getting the timong from the USB right. Apparently (but I'm no expert) it is possible to determine the timing from the external adapter rather than letting Windows determine it. That supposedly gives the Benchmark the edge.
Yes, it is theoritically possible that the benchmark is so bad, adds so much jitter of itself, that a 30 $ transport sounds like a 20000$ transprt. But I don't believe that. Simple measurements show that the benchmark has extremely low jitter, so the only plausible conclusion is that it reduces jitter from any source so much that the differences between the sources all but disappear.
'Bits is bits' in the sense that if a correct bitstream is received, the only way transports or cables can sound different is either by jitter that they introduce and that bleeds through the DAC or maybe things like noise and hum that the physical connection introduces in the analog signal. Logically, if your DAC kills the jitter bleedthrough, and your connection is noise/hum free, there can be no sound difference. Which seems to be comfirmed by the tests.
@Andy_c: We'll see you next year!
Jan Didden
janneman said:
Different DACs with the same amount of jitter may well sound differently – by stability and cleanliness of the power supplies, the design of the analog output stage, the noise level of the clock oscillator, PCB layout and more.
Joshua_G said:
We were not talking about different DACs. Engage brain before operating keyboard.
Jan Didden
andy_c said:
The TI ASRC is the src4192. Bruno Putzeys has another point of view on the src4192 vs ad1896 here: http://www.diyaudio.com/forums/showthread.php?threadid=46413
00940 said:
That's really interesting. Bruno is about as reliable a source as you can get, so I'd certainly believe him before the Benchmark people. I wonder if virtually all transports meet the "low jitter" requirement that prevents the SRC4192 from using fast mode?
I've got a Benchmark DAC1 myself, so I'd be interested to find out more. This is definitely out of my area of expertise though 🙂.
Andy,
I'll check the AX test report (measurements by Chuck Hansen) on the DAC1 tomorrow when I get home, see if there is something that helps.
Jan Didden
I'll check the AX test report (measurements by Chuck Hansen) on the DAC1 tomorrow when I get home, see if there is something that helps.
Jan Didden
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