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Old 27th April 2012, 08:42 PM   #91
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Quote:
Originally Posted by qusp View Post
Scott, did you look at the ibasso DX100 that android based SD player with the ES9018 dac I linked? if running hd600 you'll need a bit more voltage swing than just about any portable out there has by itself without adding a portable amp. it does 24/192 and has more than enough swing for your purposes.

Little pricey, but looks good. I'm even considering a Tascam portable field recorder for this purpose. I have a Fostex but the disk needs to be formated by the recorder and you can't put your own files on it, you can but only the recordings will play.
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Old 27th April 2012, 10:50 PM   #92
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You're confusing me, at best I would only count as one unit.
Which is why you'd be required to show considerably more enthusiasm and make some input. It's not an offer to sell you something, it's an opportunity to participate in an open-source development.

I said, 'I can build it, but I haven't got a dScope.'

You said (paraphrased), 'You don't need one'

I'm taking you at face value. My gut instinct is that RS is wrong, that it's possible to build a transparent device without enormous expense in testgear. I'd welcome some help in demonstrating it. Without resorting to what I think is a glib and unrealistic suggestion to employ an audio consultant.

Otherwise, as qusp points out, many of the amateur developers here might as well pack up their bags and go home unless they're happy to be basing their efforts on listening tests alone, to say nothing of those budding entrepreneurs without whose contributions the audio scene would be a far less diverse and interesting place.

I'm not talking here about cable-wallahs and other lowlives, I'm talking about with people with skills and understanding who produce working devices, and who would produce better ones with some encouragement, but who are being dismissed as 'fantasists'. This is not to say that the possession of skills excuses every and anything, there are some with high levels of expertise and positively malignant attitudes; thankfully they are few and far between. These are worthy targets for all the disapprobation an objectivist can muster.

Take a look at some of the things amateur astronomers are doing, imaging faint objects by summing multiple images in software. They're doing interesting (and useful) things that were simply impossible a few years ago, until technology changed, became a lot cheaper, and somebody had a bright idea. I don't mean that the techniques are directly transferable to this application, I'm just pointing out that ingenuity in operating new technology is key.

This is why I'd prefer to see RS bending his efforts to making high quality measurement more accessible, or even attacking some of the more slippery, sinister and less well-intentioned denizens of the forums instead of beating up comparatively benign individuals like Ti Kan.
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Old 28th April 2012, 01:11 AM   #93
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I cheat, I have access to unlimited test equipment. It would help if your tone was less like "Reason" magazine. And yes the webcam astronomers have done a great service to the community.
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Old 28th April 2012, 05:49 PM   #94
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Thanks for your input.

Bye.
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Old 28th April 2012, 06:05 PM   #95
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Where there is room for DIY is in coming up with inexpensive ways to use/build instrumentation. PC's provide such fantastic processing power, I have got to believe there is a lot of room for truly unique and innovative approaches to measurement that have not been capitalized by the traditional instrument makers. For sure, commodity stuff is so good it is hard to do better, but I contend there is a lot left to be done. As it has almost no commercial value, it is up to us.
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Old 29th April 2012, 01:49 AM   #96
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Thanks for your input.

Bye.
You're welcome.
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Old 29th April 2012, 02:03 AM   #97
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I have got to believe there is a lot of room for truly unique and innovative approaches to measurement that have not been capitalized by the traditional instrument makers.
Is anyone up for designing open source hardware for enabling null-testing to be done on DACs? I've never seen a commercial instrument supporting this but it would settle once and for all the claims of transparency in relation to S-D DACs.
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Old 29th April 2012, 02:32 AM   #98
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I don't see it as that big a problem to just cobble up a test jig, depending on exactly what kind of null testing you're talking about.

If you just want to compare the output of 2 DACs, then you take a wav file and invert one channel into the other, then output it into an SPDIF splitter and thence to the DACs. Now you mix the left input from one with the right input from the other in a passive mixer and observe the output on a scope or audition it.

Is that what you mean? I can write you a program to process the file. If you mean something else, explain...
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Old 29th April 2012, 02:46 AM   #99
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The normal kind of null testing - where we attempt to get a deep a null as possible by subtracting the output of one DAC from another. But probably better to invert in the digital domain and sum though.

I can't follow you - we don't want to 'compare the output of 2 DACs' we want to null them. But there are several issues involved which make getting a null not totally straightforward. Firstly there's the need for a reference DAC - how to choose it? Myself I'd suggest a multibit DAC like TDA1541A because it has the best measured performance at 16bits.

The next issue is delay - S-D DACs have different delays so we need a parameter to be tweaked. Its not necessarily just an integer sample rate delay as its possible an S-D DAC has fractional delay. Thirdly there's frequency response - digital filters inside S-D chips aren't flat, they have ripples and this will affect the null. If the TDA1541A in NOS were used its ZOH droop would need correcting accurately. Ideally we'd like to be able to separate out the different error factors to characterize the null better.
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Old 29th April 2012, 04:33 AM   #100
jcx is online now jcx  United States
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TDA1541 as "reference" in 2012?? - good for a laugh I guess

manufacturer's haven't been asleep the past 1/4 century - segmented ladder DAC with 20 bits, 1 uS settling 1-2 lsb INL, DNL are available today: http://www.analog.com/static/importe...ets/AD5791.pdf

you don't have to just look at "Audio" converters - medical imaging has driven perfomance well beyond "Audio" today

Last edited by jcx; 29th April 2012 at 04:38 AM.
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