What happens to an audio signal from media player to dac

[counter culture]

Originally Posted by n0vtz

I don't think this subject is well understood.

That's pretty close to the mark, but not in the sense you intended.

I had a look on CA and on HA. I think the response on HA was pitched at about the right level. 'Ask a stupid question and you get a stupid answer' is about how I'd paraphrase it.

What are you doing digging into all this stuff when you haven't got the background to pose an intelligent question? Thrashing around in the hope that somebody will spoon-feed you?

Go read some datasheets on USB DACs. TI PCM2906. Do some searches on google. Search synchronous, asynchronous and isochronous USB. All this stuff is out there, it'll only take you a few years to get to the point where you'll be able to understand the answers.

[n0vtz]

Such a pleasant fellow. :0)

Learn to take care of your own business, and others will take care of theirs. If you don't like my post, there are many other things to do. Good luck to you.

Jim

[SY]

Originally Posted by counter culture

Search synchronous, asynchronous and isochronous USB. All this stuff is out there, it'll only take you a few years to get to the point where you'll be able to understand the answers.

Or he could ask the simple and obvious questions and get some helpful answers. If you are unable to explain things clearly and politely in the face of straightforward questions, then let those who can do it do it.

[counter culture]

Not unable, unwilling.

He's just painting with so broad a brush you can tell he doesn't have the faintest grasp of the subject while looking for ammunition to reinforce his prejudices.

[mr_push_pull]

Originally Posted by n0vtz

Would you allow me to post your test at CA, so some impressions can be made over there about bit perfection? A no is perfectly ok. :0)

sure. but I made another set with even smaller difference (yet still audible on my $10 headphones driven by built-in sound card). feel free to choose whichever. see attached files.

Originally Posted by 4real

I really don't think that test says all about bit perfection. It only shows that bit error can be heard immediately. There are other ways to get imperfection, and most of them are alredy covered here: resampling and volume control. Those are far les obvious to hear them a random biterror, but still give you an output signal (lets say on spdif), that is not bit for bit the same as what is on file (assuming uncompressed audio) on your PC.

of course it only applies to data corruption at transmission side but that's what some folks claim. concerning Windows processing, I haven't searched the Benchmark Wiki page but I'd rather trust them if they say player X is bit accurate. after all, WA and foobar are free, why would they lie? and I'm almost sure there are many other publicly available tests confirming this. should we all buy/build USB analyzers to confirm it?

[4real]

Originally Posted by mr_push_pull

I haven't searched the Benchmark Wiki page but I'd rather trust them if they say player X is bit accurate. after all, WA and foobar are free, why would they lie? and I'm almost sure there are many other publicly available tests confirming this.

I woudn't doudt it. I'm merely stating that there are factors that might affect your bits. If configured correctly, it works just fine.

should we all buy/build USB analyzers to confirm it?

Why do that. Just loop your spdif back into your pc and record what you play. Remove the offset and compare original to recording.

[mr_push_pull]

Originally Posted by 4real

I woudn't doudt it. I'm merely stating that there are factors that might affect your bits. If configured correctly, it works just fine.

covered it first reply but I might have missed something.

Originally Posted by 4real

Why do that. Just loop your spdif back into your pc and record whay you play. Remove the offset and compare original to recording.

I wasn't aware of S/PDIF to USB converters and USB recorders. do you have some links?

[4real]

Originally Posted by mr_push_pull

I wasn't aware of S/PDIF to USB converters and USB recorders. do you have some links?

Thats not what I meant (would be nice to get 480mbit over spdif though) I just mean using a usb audio interface with spdif in and out. If loopback gives you no differences, then there no need for an expensive USB analyser. And even if there are differences, you can bet that it is not the USB interface that is mangling the data. It's absolutely nonsensical to think that that might happen. But I guess you already knew that

[n0vtz]

Originally Posted by 4real

Thats not what I meant (would be nice to get 480mbit over spdif though) If loopback gives you no differences, then there no need for an expensive USB analyser.

"No differences" is the problem here, and how that can be known. You can eyeball two comparative spectral representations, and say they look very similiar, but to tell conclusively you need to do a null test with them, obviously inverting one. Audacity allows you to begin to do this. It is matching them for a null test that is difficult.

Volume can be matched with a simple audacity function, but getting them matched so there is no phase differences is difficult.

No matter how careful you are (at least with audacity), where you want silence (if bit perfect in and out) when they are mixed , there will be residual noise apart from discrepancies that may exist in the system that we are actually trying to measure.

Jim

[Pano]

My goodness - busy thread!

Originally Posted by n0vtz

I'd be interested in how your verifying bit perfection, and how your measuring jitter at your analog output.

For bit perfection I do a simple test. I play a file (music or test tone) from a software player on computer A. I send that signal via SPDIF to a SPDIF input on computer B, were it is recorded. I use either a checksum or Diffmaker software to verify.

It's not hard to achieve bit perfect copies. I've even done it thru the evil K-Mixer, but that might have been at 48KHz.

As for jitter, I do not have a good way to measure SPIDF or USB jitter, but in many ways I don't care. What I do care about is if it makes a difference to the analog output of the DAC. That is the signal that matters, because that is the signal I listen to. Looking at the DAC output via FFT will show, or not show, jitter sidebands in the analog signal. They can be easily seen on cheap DACs, but are very low on better DACs.

That's about as sophisticated as my testing gets, but it works for me.