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Computer Activity Can Impact DAC Performance

jkorten

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#22
Fascinating post amirm! I've been listening to different computer OS's and different players etc. I did finally pay for (minimum) and download audiophile linux (http://www.ap-linux.com/) and it does not make a small difference. It makes a HUGE difference! And the less powerful your computer, the more impressive the change is.

Loading in AP linux is picky (you must follow ALL instructions and in detail) but in the end it isn't that hard.

Maybe you can post the difference between using plain OS-X, Windows, Linux and AP-Linux? Or Windows and Linux?

Is your ADC running on the computer's clock too? Or is it running on it's own clock?

I think the weak link is in the feeding of DACs. Unbelievable to me that these DACs don't seem to buffer and reclock the data once it is transmitted, but this seems to be the only explanation for the kind of frequency spread and jitter you are reporting.
 

Fitzcaraldo215

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#23
Careful. Amir was referring to only one particularly schiity DAC, though some others may be like that. Many other DACS are not as schiity, though they may have other issues of isolation. Still other USB DACS are well isolated from computer activity. I hear absolutely none on my galvanically isolated USB Exasound DAC when using a straightforwarward, unmodified PC with standard USB cables, for example.

I believe that, if there is a problem, it is an engineering issue at the DAC end. Modifying, replacing the computer, its innards or OS is a fool's errand, IMHO, except perhaps for quieting its acoustic noise output from fans, etc.
 
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#24
I recently came across an issue that previously I was unaware of. Apparently, RF emissions from motherboards are sometimes an issue with compliance body certification. A solution employed by the MB mfr is to adjust the clock frequency (typically in a +/- 5% range) which changes the emissions frequency, and can lead to compliance certification. The setting can be adjusted in BIOS. If the MB was shipped with the adjusted clock, it makes clock sync for audio problematic, and adds jitter (or at least that is the claim).

There is a Wikipedia page on the subject (not particularly helpful, but some). I ran across it at the AQXOX website (manufacturer of audio components, Germany)

" ...
Optimize PC´s BIOS for AUDIO-Streaming - switch off the CLOCK-spreading / clock spread option / spread spectrum - less Jitter

If you enter the PC´s BIOS you will find somewhere in the voltage/clock options the CLOCK Spreading or Clock Spread Spectrum or SPREAD Spectrum option. This function is actually meant for EMI (electromagnetic radiation) test during the CE-test of the Mainboards. If the Motherboards during the CE - certification-tests for high radiations in a certain frequency range produce to high distortions, caused by possible overlay of frequencies (also harmonic waves) and thus a reinforcement (constructional interference) of the radiated signal. This radiation behavior can be changed by letting the systemclock not longer precisely work on a specific frequency but changing its frequency very fast. The clock-frequency fluctuates and thus flattens the spikes because SPREADING it on a broader frequency band. The BIOS adjustment possibilities can look like: 0.25%; 0.5%; 1.5%; Enabled and Disabled. Disabled means the Spreading is switched off. This is the best option, however you should restart it, if radio or TV are disturbed. Disabled improves also the PC performance. Sonically effects: What the CLOCK Spreading now to do with the sound? Very simple, an instable/varying system clock produces JITTERS, all the same whether the audio data are transmitted via USB or over an internal or external sound-port or soundcard by SPdif or TOSlink.

See what wikipedia says about one of the effects of this spreading - the clock skew
http://en.wikipedia.org/wiki/Clock_skew
..."

From: http://www.aqvox.de/tech.html

If present, this would be a model-by-model variation, so would require a check to determine if it's an issue for your specific hardware.

Note: First Post
I didn't know of this forum previously, was pointed to it by a UK reseller, Keith at purite audio (~co.uk)
 
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amirm

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#26
My welcome also Johnny2Bad.

Spread spectrum techniques are quite effective for passing emissions standards where "jitter" is put to good use. Let's say we have a peak at 500 Mhz created by a clock at the same frequency. If we apply random jitter of +- 1 Mhz, it will take that peak and spread across a 2 Mhz region now. Since the total energy remains the same, the peak by definition goes down. Of course jitter created must be within the range that doesn't disrupt the timing of the circuit and cause it to fail. This technique is used more often in switchmode power supplies where there is no consequence in timing being different by that manner.

Here is a nice picture that shows the effect (it is not always this effective) from Maxim (chip company):

 
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#27
Makes perfect sense. The articles I read said that +/- 5% was the problem area. However from your graph I wouldn't want to see anything too near those 91 and 93.7 Mhz values. Also that you could remove the spreading in some deep BIOS settings, recommending you check for interference with nearby devices after you do so.
 
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#28
Definitely not a problem with WMP. My team at Microsoft wrote it :).
Um. That's not a great claim to fame. If you like, we can discuss specific issues, but given the date of your post, I expect that it's water under the bridge at this point.

ObOnTopic: No, that doesn't speak well of that DAC. But the graphs are gone, so I'd have to see them again.

Feel free to PM me on either subject. Cheers!
 

amirm

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#29
Um. That's not a great claim to fame. If you like, we can discuss specific issues, but given the date of your post, I expect that it's water under the bridge at this point.
Didn't say it as a claim to fame but rather, having specific knowledge of how it works.
 

Krunok

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#30
I just installed Volumio on a Raspberry Pi 3 B+ and connected USB to SPDIF bridge to it. I'm using Linn player Kinsky to stream via UPnP to it and it sounds fine. The same thing when using BubbleUPnP from Android phone. I contacted Volumio developer and he told me that it should work with practically all USB DACs on the market.

Tried Foobar as well but its UPnP plugin (which is still in beta) cannot send 24 bit output, when you set it to 24 bit it sends 32 bit instead which my bridge doesn't support. I was also not able to get it to send SACD (DSD64) correctly. Foobar was also not able to see my Denon HEOS system in the other room as a renderer while Kinsky and BubbleUPnP recognised it and are playing to it without problems.

All 3 players were able to fetch music from my Synology NAS running UPnP Media Server.

Unfortunately I can't measure how well it performs, but I put more trust in Raspberry Pi 3 B+ running only Volumio than my notebook which does all sort of things while playing to USB.
 

Krunok

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#31
Here is what made me do this: I mostly listen to the music in the living room, but my notebook is quite far from my audio equipment, more than 5m of USB cable would be needed, which would impact playing some HiRes material, not to mention make my wife to throw the vble and me out of the flat. :D

So obviously, another solution was needed. I tried using USB to Ethernet server Silex DS-510 and it worked, but really flawlessly. Every time when player on my notebook (any player, they were all behaving the same) was changing bitrate via ASIO or WASAPI, as next song was having different bitrate than the one playing, there was a period of 5-10 seconds of sounds as if player was fastforwarding audio tape - at first I found it was amusing but later it started to annoy me. It seems that Silex does this with all Singxer USB DACs/bridges probably due to a mismatch between driver and Silex firmware. I tried using the generic Windows 10 driver which didn't manifest that behavior but I was experiencing random dropouts, say 1 sec of dropout each 5-10 minutes. Here I would also like to mention that my WiFi network is pretty good . I can, for example watch movies with bitrate higher than 40Mbps without any issues.

So, I start to Google for alternative solution and found this monster: https://www.linn.co.uk/hifi-separates/network-music-players/klimax#klimax-ds

I got cooled down the moment I saw the price (15800 GBP in UK, roughly $21400) . Yep, no typo here, I checked the figure twice. Measurements done by Stereophile can be found here for anybody who think they can justify the price.
https://www.stereophile.com/content/linn-klimax-ds-network-da-processor-measurements

As I don't have $21400 to spend on DAC I turned my head to my Singxer USB bridge and I came to conclusion that if I spend $50 on Raspberry Pi 3 B+ (power supply included) I can make two of them work together as an UPnP renderer or, if you want, Network Media Player. Pursuing the even greater irony, I bravely downloaded Linn music player that goes with the Klimax DS, et voila - it works perfectly! :D
 
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