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Old 1st December 2011, 04:18 AM   #411
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Originally Posted by RocketScientist View Post
Many (most?) players are making the exact same calls to the exact same APIs. And as long as they're delivering a bit accurate stream (i.e. no DSP, resampling, etc.) you'll get exactly the same sound (i.e. via DirectSound in Windows).
You'll get the same bits, but the same sound? Some evidence supporting this claim would be nice to see. After all, no sound comes out of the computer itself, the sound is dependent on a whole host of supporting equipment.

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I would suggest the differences many claim to hear are either due to different settings, or they're just the usual well documented differences our brains serve up in sighted listening tests even when no differences really exist.
How are you going to test your hypothesis?
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Old 1st December 2011, 04:22 AM   #412
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1. Even in USB soundcards, noise from the PC gets to the sound card via the power supply leads. Good filtering helps but unless u have full opto-isolation, some PC noise will feed through. Granted, the noise feedthrough though measurable with a scope, is often not audible.

2. It is good that you have actually looked at the USB bits transferred from PC to USB soundcard. But were those measurements done with up to 192khz/24bit async out with rate feedback with different buffer sizes in the drivers? Some of us have heard differences in SQ just with different driver buffer size settings.

I agree that listening tests are subjective. But theoretical arguments and measurements can also be misleading.

Look back at the debate about SQ between solid state and tube amplifiers. You can measure the THD and argue that since solid states have 0.000001% THD MUST sound better than vacuum tubes with 0.1% THD !!! But does THD tell the whole story?

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Old 1st December 2011, 05:29 AM   #413
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Alexlee188 & Abraxalito, I don't want to de-rail this thread with OT discussion of tube amplifiers, etc. But bits are bits and if the external equipment remains the same (i.e. the USB DAC) those bits will deliver the same result every time if they're the same bits. If anyone has a plausible explanation as to how that's not the case, please share it?

My USB captures were all garden variety UAC1 isochronous playing normal 44 Khz CD audio at 16 or 24 bits which should cover about 98% of people playing music on a USB DAC. Short of dropouts if it's too small, and latency (which doesn't effect SQ), the buffer size won't make any difference either.

I don't think there's anything misleading in what I'm trying to say. Even the hard drive noise in the USB power is a rather extreme stretch, especially for a DAC like my Benchmark DAC1 that doesn't even use the USB power for anything.

I also have a full ABX box and it should be possible to set up a blind test with 2 players at a time and compare them. If they're delivering the same bits, I can promise nobody will be able to tell them apart. In fact I'll bet money on it.
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Old 1st December 2011, 05:42 AM   #414
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Originally Posted by RocketScientist View Post
ABut bits are bits and if the external equipment remains the same (i.e. the USB DAC) those bits will deliver the same result every time if they're the same bits. If anyone has a plausible explanation as to how that's not the case, please share it?
That's the wrong way around. Science is done by the one who makes the claim supporting it, not the naysayers spending their time shooting down unsupported assertions.
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Old 1st December 2011, 06:51 AM   #415
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Quote:
Originally Posted by RocketScientist View Post
bits are bits and if the external equipment remains the same (i.e. the USB DAC) those bits will deliver the same result every time if they're the same bits. If anyone has a plausible explanation as to how that's not the case, please share it?

My USB captures were all garden variety UAC1 isochronous playing normal 44 Khz CD audio at 16 or 24 bits which should cover about 98% of people playing music on a USB DAC.
Digital audio channels are two dimensional: they incorporate instantaneous values with timing of those samples. If the same bits are delivered, it doesn't guarantee that the timing of the conversions is identical, and thus you can have significant and measurable noise by merely the effect of clock errors.

Therefore, the only case in which your "identical bits" claim is valid is where the USB DAC is the master clock. Otherwise, there could easily be variables.

It may be worth pointing out that all UAC transfers are isochronous. That's the only option for UAC. Where the options come in are asynchronous, synchronous, and adaptive. Asynchronous is the one you want, because it does not depend upon the USB for clock, so all you need is that the computer keep up with sending the data. Some folks may be happy with SPDIF or USB synchronous or adaptive, but there are certainly more variables there which are dependent upon the computer that hosts the USB.
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Old 1st December 2011, 07:09 AM   #416
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@rsdio, isn't it the USB hardware in the PC that determines the timing of the USB data? So regardless of what mode the USB DAC is using to generate MCLK, the USB timing from a given port on a given PC is fixed.

Put another way, the player software is, through various API's and layers within the OS and driver, simply keeping a hardware buffer reasonably full and the USB hardware in the PC is then shipping off the bits in a very independent fashion. It's in no way related to the CPU clock or the load on the load on the CPU. It's just an independent chunk of hardware emptying a buffer. The only way the software can have any influence is to let the buffer run empty.

The only variable alexlee188 was talking about changing is the player software. Nobody has explained how player software can alter the timing of the USB hardware PHY in the PC? The software can alter the bits being sent, which is why I used the USB analyzer to look at the packets and verify it really is the same data.

So same data, sent with the same timing, by the same hardware, to the same hardware, equals same sound in my book. I completely agree different DACs can interpret the same bits differently due to jitter issues. And I agree different PCs/USB ports can send the data with more or less jitter. But we're just talking about comparing software here.
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Old 1st December 2011, 07:12 AM   #417
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So same data, sent with the same timing, by the same hardware, to the same hardware, equals same sound in my book.
Thanks for clarifying that its just your opinion.
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Old 1st December 2011, 07:18 AM   #418
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Steady on the wheel guys! We're trying to trust both our ears and our scientific knowledge of analog and digital systems here. There are so many gopher holes to step into. Power, clocking, IV conversion etc. Getting the bits correctly through the hose is just one of them. We welcome both analog and digital hackers here. Personally, I believe every single subsystem has potential for improvement. Please direct "digital is flawed", "transistors are flawed" etc. elsewhere. I can explain for an hour why there is an audible difference between SPDIF cables. But I choose not to do it here.

If you wonna be constructive, feel free to buy a kit from George or from myself, change the output filter, mod the PSU, install a battery, or build your own Analog Board from scratch. In short - go nuts. But please do it constructively.

The _results_ of true blind tests of different players would be very welcome.

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Old 1st December 2011, 07:25 AM   #419
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I'm trying to be constructive. Myths are propagated by posts such as alexlee188's. It's useful to explain what really matters, what doesn't, and why. There's a lot of confusion about how USB audio really works and this thread is about USB DACs. It's useful to know the software, short of being bit accurate, doesn't matter for sound quality with a USB DAC of any sort.

To put it another way, there's no way for software to alter the timing of the data going out the USB port in anything resembling a predictable way. And if that's true, there's no way the bright guys behind Foobar can design their software for any better sound quality than the ones behind PurePlayer.
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Old 1st December 2011, 07:30 AM   #420
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Quote:
Originally Posted by RocketScientist View Post
I'm trying to be constructive. Myths are propagated by posts such as alexlee188's.
And your 'there's no sound difference if the bits are the same' claim doesn't pass muster as a myth? Shurely shome mishtake.

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To put it another way, there's no way for software to alter the timing of the data going out the USB port in anything resembling a predictable way. And if that's true, there's no way the bright guys behind Foobar can design their software for any better sound quality than the ones behind PurePlayer.
In async USB (which is what this thread's about) there's no way for the software to alter the timing at all at the DAC end.
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