Eliminating jitter "completely" - Benchmark DAC1 approach - Page 2 - diyAudio
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Old 30th November 2002, 01:33 AM   #11
jwb is offline jwb  United States
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I hadn't considered the timing on the B-B parts, but it seems like an odd choice. I've heard, but not verified, that some filters like the PMD-100 transfer the word to the DAC in a burst, not at master clock intervals.
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Old 9th April 2005, 09:21 PM   #12
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Hi Halcyon,

I have just come across your 'Benchmark DAC-1' enquiry in diyAudio.

Did you construct or buy, and did you obtain anything good that you think betters the Benchmark ?

Should very much appreciate your reply so that I might head straight for good digital playback using output from a Pioneer DVD into home made power amps/spkrs.

Thanking you in advance ............. Graham Maynard.
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Old 10th April 2005, 01:47 AM   #13
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I've had a benchmark apart here,

akm spdif reciever, ad1896 asrc with a basic crystal oscillator hanging off it, ad1853 and opamps for output stage with some ic for headphone out


3 pin regulators, layout is long way from optimal for a mixed digital/analog pcb


no rocket science, love their trademarks they have cooked up, the marketing spew is a great rehash of the akm/ad pdf's




Mark
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Old 10th April 2005, 10:52 AM   #14
Bricolo is offline Bricolo  France
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Can someone explain me the advantage of running the ASRCs'output (AD1986) and the DAC (AD1853) at a 97.65625 kHz clock instead of a 96 kHz one? Can this give advantages, when the input is 96 kHz?
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Old 10th April 2005, 02:46 PM   #15
Previously: Kuei Yang Wang
 
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Default Re: Eliminating jitter "completely" - Benchmark DAC1 approach

Konnichiwa,

Quote:
Originally posted by halcyon
I was intrigued by the apparently *excellent* AP One measurement results for the Benchmark Media DAC1 (available at: http://www.benchmarkmedia.com/digita...%20Rev%20A.PDF ).
I am not sure why you call them "excellent", I'd call them "par for the course" and of course, measurements like those taken for the DAC1 have yet to be shown to have a good (or in fact ANY!) orrelation with percieved "good sound".

Quote:
Originally posted by halcyon
The jitter immunity this DAC provides is in my personal understanding phenomenal. I have never seen such Audio Precision results for any commercial DAC for which I've seen properly done measurements.
I have never seen measurements of Jitter done in the way Benchmark do either. They seem to have invented a specific new type, probably because it offers good measurements with what they got.

That said the measurements taken by stereophile also show low clock jitter. How this is achieved we cover soon.

Quote:
Originally posted by halcyon
The other measures specs are excellent as well.
They are? I thought they where within the limits provided by the Chip makers standard application spec's. No skill needed, just use the standard eval circuit.

Quote:
Originally posted by halcyon
- It uses AD1853 DAC ICs in a mode that achieves 115 dB stopband attenuation
So do many other DAC's.

Quote:
Originally posted by halcyon
- It operates AD1853 at constant 97.65625 kHz sample rate, regardless of input input sample rate, thus shifting the transition band higher (with input sample rate of 48 kHz) than with a sampling rate of 48 kHz would do
Or in plain english, Benchmark wanted to avoid paying a slight premium for an oscillator with the "correct" 24.576MHz frequency for their ASRC (Asyncronous Sample Rate Converter) and used a 25MHz one which is cheaper. Someone in marketing then said "Hey, we can make that a "feature"!" and so they did.

Quote:
Originally posted by halcyon
- At 96 kHz input rate the fixed clock it only gives DAC1 a transition band shift of c. 860 Hz upwards, still enough to eliminate most transition band problems
I may be forgiven for saying so, but when using semi-stochastic signals, such as music, the ASRC used to implement the DAC1's jitter rejection and "fixed clock" have a demonstrated negative sonic impact. I am not sure what "transition band problems" are being alluded to, but the shift by less than 1KHz or even the shift by 53KHz does not eliminate anything, it merely moves any transtition bandproblems from the DAC's Oversampling filter (which is of a very good spec, if poor sound) into that in the ASRC, which is commonly of lower quality. If the DAC's OS Filter or that of the ASRC are better is a question specific to the chips used.

Quote:
Originally posted by halcyon
- DAC1 uses a FIR low pass filter to incoming PCM stream (before AD1853) with a passband at 44.29 kHz and stopband at 53,37 kHz (achieving 125 dB attenuation)
In other words, it uses a bog standard digital filter, liek everyone else.

Quote:
Originally posted by halcyon
- It claims to eliminate almost all transition band effects (including aliasing intermodulation distortion effects) for signals with input sample rate of 96 kHz or less.
One would need to add that the same is true for any other DAC in the world using the same ASRC & DAC, both of which are commodity items.

Quote:
Originally posted by halcyon
For 192 kHz the data is (I assume) downsampled to 96 kHz and processed further from that.
The DAC does not accept 192KHz input.

Quote:
Originally posted by halcyon
- I think the measurements (if valid/repeatable) prove this is not just mere marketing hyperbole.
I think they are nothing but, because there is nothing outstanding in these measurements, for the basic chipset that is being used. There is no technology present except those made available as commodity by the various chipmakers.

Quote:
Originally posted by halcyon
- It also has a variable volume headphone output (just off the DAC) (op-amps?) with an output impedance of near 0 Ohm to minimize distortion to various headphone loads.
In other words it has a headphone output. Most headphone outputs are like that, you know.

Quote:
Originally posted by halcyon
1) Are the approaches used the above 'common' within the DIY DAC community here? Esp. the fixed non-standard sample rate and relate FIR filtering at shifted transition band?
No, most DIY'er pay more attention to getting things right according to their particular espoused principles and do not go out of their way to save a penny or two. As said, the entire tirade you produced is the "marketing speak" description of a system entierly traditional in design and execution with the only "features" that diverge are marketing spin on money saving measures.

Quote:
Originally posted by halcyon
2) Has anybody here actually measure his/her DAC with AP One/Two or Miller Audio Research QC units to assess technical performance? Or does anybody have any measurements from any other DAC to compare?
The APOne does not measure jitter. The Miller analyser is very expensive and rare. I have done simpler tests (FM demodulator on WCLK) and found that that low jitter seems to correlate with better sonic transparency and an absence of edginess.

Quote:
Originally posted by halcyon
3) Would $799 USD + courier + VAT of 22% be a too high a price for a professional audio DAC like this,
The cost is resonable for the package. However, I would suggest to only buy the DAC without audition if you have the right to return the unit if you do not like the way it sounds.

Quote:
Originally posted by halcyon
Do you think the DIY community could equal or outperform this TODAY, that is, is there a DIY design that at least in technical performance is better than what DAC1 claims?
Much will depend on your definition of "better perfornamce". A DIY DAC using AD1853 & SRC1896 and a generic 25MHz clock module will provide the same performance at a notional cost. I believe PCB's for such are available from several chinese sources.

Quote:
Originally posted by halcyon
Anything else you wanna add or ask?
I beleive in terms of subjective "good sound" even the most basic TDA1543 based Non Oversampling DAC will outperform the Benchmark, because of the use of non-traditional engineering principles that correlate well with percieved "good sound", despite poor measurements in the traditional sense.

Quote:
Originally posted by halcyon
Can you design a DAC that measures on the bench equally well or better than DAC1?
Any semi-competent designer can.

Quote:
Originally posted by halcyon
Can an inexpensive DIY DAC achieve the level of jitter immunity that DAC1 does,
As long as it uses a similar ASRC, of course....

Quote:
Originally posted by halcyon
The measurements are phenomenal, I'm sure nobody can deny that?
Are they? There are by now many DVD & CD Players of quite low cost which have as low or lower Jitter.

Quote:
Originally posted by halcyon
So, are you in fact saying that all this is 'old news'
It is. Look at the release date of the various ASRC's....

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Old 10th April 2005, 02:48 PM   #16
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Konnichiwa,

Quote:
Originally posted by Bricolo
Can someone explain me the advantage of running the ASRCs'output (AD1986) and the DAC (AD1853) at a 97.65625 kHz clock instead of a 96 kHz one?
The ability to use Computer grade (and thus very high volume and low cost) 25MHz oscillator and thus saving a buck or two on the whole thing.

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Old 10th April 2005, 05:04 PM   #17
JohnW is offline JohnW  Hong Kong
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“Or in plain english, Benchmark wanted to avoid paying a slight premium for an oscillator with the "correct" 24.576MHz frequency for their ASRC (Asyncronous Sample Rate Converter) and used a 25MHz one which is cheaper. Someone in marketing then said "Hey, we can make that a "feature"!" and so they did”

You’re very mistaken on your above statement – while some of Benchmarks “comments” are questionable - It’s correct and preferable not to operate an ASRC at a “Drifting”1:1 ratio.

SRC can produce odd effects when operating very close to a 1:1 ratio – OK if fixed, but if the frequency’s between the primary and secondary side of the SRC drift around a 1:1 ratio then you can get “strange” artifacts. Some SRC claim to be OK with 1:1 ratios – but I still prefer to avoid this situation.

John
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Old 10th April 2005, 06:57 PM   #18
gmarsh is offline gmarsh  Canada
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I'm about to send out parts/PCB orders for a headphone DAC which contains a SRC. I originally picked a 49.152MHz oscillator with excellent phase noise characteristics - it turns out I can get a 50, 48, 27 or 25 with the same characteristics from the same manufacturer for less.

And I just might do that, considering going with 50MHz will save $0.15 CDN on a ~$300 project.

Interesting point about the 1:1 ratio...
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Old 10th April 2005, 07:06 PM   #19
00940 is offline 00940  Belgium
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Default Re: Re: Eliminating jitter "completely" - Benchmark DAC1 approach

Quote:
Originally posted by Kuei Yang Wang
I may be forgiven for saying so, but when using semi-stochastic signals, such as music, the ASRC used to implement the DAC1's jitter rejection and "fixed clock" have a demonstrated negative sonic impact.
I'm curious here. Where, how and when was the AD1896 "demonstrated" to affect negatively the sound ?
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Old 10th April 2005, 07:38 PM   #20
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Default Re: Eliminating jitter "completely" - Benchmark DAC1 approach

Anything else you wanna add or ask?

I'm asking, because I'm in a market for a new DAC, it needs to be faultless even with jittery sources and can't cost an arm and a leg (well, that's all relative as $800 USD is a quite a chunk of money to me personally).

-----------------------------------------------------------------------------------
There is no dac I have heard that:

1. Is not cable dependent;

2. Has input circuitry that can deal with jittery sources and 'cure' them.

3. Sounds 'perfect' because measurements are 'perfect'.

4. Those with srcs or asrcs all sound individualistic due to resampling or unpasmapling.

5. The best I have heard is dCS stuff with upsampling to 174.4/24.

6. Sounds good with NE5532 opamps for extended periods.

The Benchmark uses NE5532s. For $1000, one would have thought they coulc put in some decent sounding opamps that may not measure as well.

As an eaxample, the Assemblage dejitterer/src with I2S out measures very well but sounds hifi. So does their dacs.
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