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  #241  
Old 08-18-2011, 02:06 PM
inarc inarc is offline
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Originally Posted by NwAvGuy View Post
But as far as "re-sampling" that's a complex, and controversial, topic. One can argue all one bit delta-sigma DACs (virtually all DACs these days) "re-sample" as they all operate at a vastly higher clock rate internally.
Sorry for the misunderstanding. I should not have called it "internal resampling" as I have no problem with internal oversampling. What I mean is that the USB chips of both the U3 and X-Fi HD do not appear to support 44.1 kHz natively, so the audio streams will in this case first have to be resampled to 48 kHz, which is often detrimental to sound quality.
The following RMAA measurements of the X-Fi HD - if they are to be trusted - illustrate my point:
24 bit, 44.1 kHz, external loopback
24 bit, 48 kHz, external loopback
24 bit, 96 kHz, external loopback
(Full article)

Last edited by inarc; 08-19-2011 at 08:46 AM.
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  #242  
Old 08-18-2011, 02:22 PM
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Sorry for the misunderstanding. I should not have called it "internal resampling" as I have no problem with internal oversampling. What I mean is that the USB chips of both the U3 and X-Fi HD do not appear to support 44.1 kHz natively, so the audio stream will first have to be resampled to 48 kHz, which is often detrimental to sound quality.
So you're concerned the operating system, or native operating system driver, is quietly re-sampling the audio? If that's true that should already be well documented behavior that Windows, and Mac native sound drivers are mis-reporting the hardware status.

And, I'm curious, why do you think natively 44 Khz supporting is a problem? AFAIK, it's just as easy to support over USB as 48 Khz. The audio clock is embedded in the data so the "link" doesn't really care as long as you don't exceed the maximum bandwidth.

Generally I've trusted what the dScope's software (that directly communicates with any USB sound device) reports back from the driver. But I suppose the driver could be "lying" and reporting 44 Khz when it's really 48 Khz.

I do have a USB 2.0 bus analyzer that time stamps every frame with 16 nS resolution. It can easily determine the actual average data rate over the USB link. It would be interesting indeed if it's 48 Khz when the driver is reporting 44 Khz to the operating system and applications. But someone should have discovered that a long time ago if it's true and beat Microsoft and Apple over the head.
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  #243  
Old 08-18-2011, 03:03 PM
inarc inarc is offline
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So you're concerned the operating system, or native operating system driver, is quietly re-sampling the audio?
Yes, drivers report the supported bit depths and sampling rates of their respective devices and it is up to the operating system (mixer, I presume) to convert unsupported formats. (It's conceivable, of course, that drivers could also misreport supported formats and do the conversion themselves.)

This is how the X-Fi HD advertises its capabilities to the OS:

(Courtesy of your very own Head-Fi.)
And another thread: Any plans to implement 44.1 Khz support ? Creative X-FI HD USB

As for the U3, Asus lists 48 kHz as the sole supported sampling rate. Whether that is meant to include 44.1 kHz, I don't know, but according to one review, "48kHz is the only option".

And now I feel bad about derailing this thread.

Last edited by inarc; 08-19-2011 at 08:42 AM.
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  #244  
Old 08-18-2011, 03:12 PM
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Yes, drivers report the supported bit depths and sampling rates of their respective devices and it is up to the operating system (mixer, I presume) to convert unsupported formats. (It's conceivable, of course, that drivers could also misreport supported formats and do the conversion themselves.)
Ah! That's VERY different. Thanks. That's not ideal news and something I'll certainly investigate further. If they really are forcing a conversion on the PC side for 99% of the digital music on the planet that's really sad engineering--especially given both Creative and Asus are marketing the respective product lines as being audiophile-grade products.

It's my hope they might be instead trying to let you pick the maximum sample rate and the actual link will still run at 44.1 Khz. It shouldn't be too hard to figure out what's really going on. But if you can't get bit accurate output that's not a good thing even if I'm sure many would still be happy with the result.
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  #245  
Old 08-18-2011, 03:13 PM
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I have read that creative soundcards upsample everything. . . seems like a fail to me, but idk.

I tried playing mp3's on my PS3 and it took a while for me to figure out it sounded like crap b/c it upsampled everything to 48k by default.

Not something I would buy.
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  #246  
Old 08-18-2011, 03:27 PM
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One of the reasons I wanted to test the X-Fi is I understood creative was NOT doing their historical "upsample everything" approach with the X-Fi line. But, to be honest, I didn't research it very deeply.

For the record, many (most?) DAC chips need to be set up for a given sample rate for the digital filtering and other things to work correctly. Many can't automatically sense the actual audio clock. That often requires a microcontroller in the DAC to manage things.

So if you have DAC that accepts both 44-48 Khz via USB and 24/96 via S/PDIF, and it doesn't have a microcontroller in it, you may have a problem as a designer. You either up-sample the 44 and 48 to 96 Khz and always run the DAC chip at 96 Khz. Or you have to add a microcontroller to sense the clock rate and configure the DAC chip accordingly. Or you use parts that can play nice together via hardware configuration pins but those combinations are rare and often prevent using the most "fashionable" DAC chips.

Of course, if you're a certain eBay vendor, you just permanently configure the fashionable DAC chip for 24/96 and it totally falls on its face when using USB at 16/44 (I have just such a DAC sitting right here).
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  #247  
Old 08-18-2011, 03:32 PM
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Marvin the Martian Marvin the Martian is offline
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16/44.....how pedestrian! I insist on 24/192.
(not really....just wanted to see if I could type that without laughing, and I couldn't.)
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  #248  
Old 08-18-2011, 04:44 PM
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Hello,

i eagerly followed this thematic, as for a long time i wanted to have a good amp and try to get a little bit into the world of DIY-Electronics. But starting with the parts i got a little bit into trouble. Is there somebody from Germany or even better from Berlin who got all the parts coverd and could tell me where to get them?
Would be much appreciated, thanks in advance.
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  #249  
Old 08-18-2011, 04:58 PM
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Have you tried http://de.mouser.com ?

You can get the enclosure (and perhaps euro AC wall adapter) from: http://de.farnell.com

Schaeffer AG can make the front panel.

That should cover it and if Mouser Germany doesn't have a part or two, check the parts list for the Farnell substitutes.
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  #250  
Old 08-18-2011, 05:40 PM
Oliver Freeborn Oliver Freeborn is offline
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What about the following enclosure:
http://www.rapidonline.com/sku/Tools...124471/30-3557
http://www.evatron.com/upload/ecbpdf-evatron.pdf

The Evatron enclosure is cheaper than the B2-080 by a considerable margin. Also, Farnell has a minimum card order of 20 whereas rapid will just charge 5.95 for delivery.

I've got a feeling this as an opportunity only available for UK peeps.
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  #251  
Old 08-18-2011, 06:02 PM
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Nice find Oliver! That looks like exact same aluminum extrusion. But there is a catch. The B2-080 includes the front and rear panels and the screw hardware. The Evatron EBS 80 does not. So you have to also order the panels, PBN 1, and the screws, SC 8. And, unless I just can't find them, Rapid doesn't seem to stock either one.

The front panel isn't a big deal for those buying one from Front Panel Express or Schaeffer in Germany. But the rear panel kind of is.

If someone finds the panels, let us all know?
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  #252  
Old 08-18-2011, 06:11 PM
Oliver Freeborn Oliver Freeborn is offline
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Panels:
http://www.rapidonline.com/Tools-Fas...ssories/124471

I didn't realise that didn't include panels etc. That is very odd. Even worse - the end plates are on backorder. I'll send rapid an email to see when the end plates will be back in stock.

You *might* be able to get single units direct from www.evatron.com. I'll be getting my stock directly from Evatron (black ones) but I don't know if they do personal sales.
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  #253  
Old 08-18-2011, 06:14 PM
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Thanks, let me know what you find out.
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  #254  
Old 08-18-2011, 08:48 PM
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Could someone please do me a favor and try to have DeadlyLover on Head-Fi post here, on the diyAudio thread, or contact me directly? He's having one problem after another with his point-to-point O2 and I'd like to help him.

Granted, I strongly urged against building the O2 point-to-point for a whole bunch of reasons like grounding, wiring errors, op amp stability, etc. But he's already gone down the road and it would be good to try and help verify if his O2 is even working correctly. The latest is he's complaining of a big turn off thump and even comparing it to the Schiit Audio debacle. But there's no comparison. Schiit was 2.5+ volts over 250 mS. This is 1/10th the voltage over 1/10th the time which literally makes it about 1/100th the transient. I also mentioned the thump in my first article since day one and again in the last article.

Here's the "thump". It's only 250 mV RMS (350 mV peak) and it's only about half of one 25 hz cycle. The bass out of an iPod is far stronger. So yeah it's audible, but it's nothing to worry about. If he's getting a much stronger thump he may well have gotten something wrong. There's more in the the Circuit Description section:

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  #255  
Old 08-18-2011, 09:05 PM
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I sent him a PM on Head-fi...
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  #256  
Old 08-18-2011, 10:45 PM
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I'm not clear on why you want to add the switch? If you unplug the AC power the O2 runs from battery. If you plug in the AC power, even with the batteries in place, it runs on AC power (and also charges the batteries). So it automatically switches by itself.
oh thanks, the components in my library doesnt represent correctly and im confused making me wanna make the switching.

thanks for your reply NwAvGuy.. im looking forward to build this soon and give opinions and feedbacks.
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  #257  
Old 08-18-2011, 11:00 PM
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IMPORTANT!!! All the late nights working on the O2 have caught up with me. In producing the turn on/off transient plots earlier I went quite a bit further and discovered a low battery condition problem that came about with the last revision. I have agdr to thank for the "spark" as his simulations revealed something I hadn't seen in earlier testing. So I was curious where the discrepancy was.

The net result is there's been a minor change to two lines on the parts list. If anyone has already ordered parts, there's a workaround. But, ideally, C16 & C21 drop from 0.22 uF to 0.022 uF. And C22 increases from 0.47 uF to 1.0 uF. I'll have the new docs up shortly. There are more details in the other O2 thread.

This is only applicable to battery operation. If you already bought parts but only intend to use AC power it's a non-issue.

I had planned to walk before I ran with with O2. I didn't expect 130 boards to be ordered in the first batch. That's a lot of responsibility so I've trying, time permitting, to do more testing before those boards are actually ordered. I'm also encouraging everyone to hold off buying parts until the board are ordrered The parts will still arrive first so there's no reason to order them sooner. Sorry for the glitch but it's much better caught now than a month from now.

As a tiny bit of consolation, here's some colorful O2 stuff on my bench :

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Last edited by NwAvGuy; 08-19-2011 at 12:02 AM.
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  #258  
Old 08-19-2011, 12:10 AM
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Pretty colors.
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  #259  
Old 08-19-2011, 04:31 AM
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Pretty colors.
Ooohh.... That purple one sure is screaming for an acryllic enclosure. But that would require me to vastly improve my soldering skills
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  #260  
Old 08-19-2011, 06:10 AM
Oliver Freeborn Oliver Freeborn is offline
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For the UK people interested in rolling with the Evatron enclosure - I just had a word with Rapid and they seem to think that delivery time would be 7-10 days for the back ordered end plates.

I'm also talking with Rapid r.e. black versions and they are currently getting me a quote. However, it looks likely that there will be a higher MOQ for them.
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