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Audio-gd Digital Interface - Page 193

post #2881 of 4002
Quote:
Originally Posted by tim3320070 View Post

From what I can see, the "distortions" he is "hearing" are way beyond human hearing, at -130db. What a joke, and a long winded one at that.

 

What is below -130 dB?  Clearly the graphs show noise and distortion metrics above -130 dB - granted without substantial differences in magnitude but differences in level and frequency are clear to be seen.

 

Either way this thread is not the right place to be discussing this.


Edited by drez - 5/23/12 at 5:30am

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post #2882 of 4002
Quote:
Originally Posted by drez View Post

What is below -130 dB?  Clearly the graphs show noise and distortion metrics above -130 dB

 

I think tim3320070 meant distortions that only appear with some cables, but not others.

 

In any case, I am not sure how much useful/reliable/repeatable these graphs are. Other than the usual limitations of RMAA, they seem to have been made by a loopback from the USB DAC to an internal sound card in the same computer. This likely created a ground loop between the USB port and the input of the sound card (something that does not happen under normal usage conditions of the USB DAC), and variations in the noise floor could have been related to that.

post #2883 of 4002

I wouldn't be surprised too if he had these variations on ground measures from one measure to another using the same cable.

post #2884 of 4002

I thought ground loop was caused by a potential difference between ground points?  EG. connecting a computer at one wall outlet to an amplifier at another wall outlet?  Have you had this sort of ground loop happen to you before?

 

The accuracy of the computer Essence ST soundcarrd's ADC seems pretty good at 118 dB. ground loop and ADC/DAC accuracy does not explain correlation between performance data of the different USB cables between the two (or more) tests.

 

Anyway why does anyone care how an USB cable affects the performance of a mid tier USB card?  Anyway you can count on audio skeptics to 1) question the validity of data and 2) question the audibility of the results.  I mean honestly is there even an equivalent study that shows USB cables to not measurable alter distortion? (this is a genuine question)

 

Any---way if you fell like huffing and puffing about why you think USB cables don't matter there is already a thread for this :http://www.head-fi.org/t/554008/dont-get-why-audiophile-usb-cable-would-improve-sound-quality/795#post_8395914  Discussion there will not be off-topic.

post #2885 of 4002

My new DI-DSP is shipping next week (along with new NFB-16)- how's that for back on topic! And I'll be running my high-end USB printer cable to it along with my $4 Monoprice power cable as well- sorry, couldn't help myself.


Edited by tim3320070 - 5/23/12 at 6:33pm
post #2886 of 4002
Quote:
Originally Posted by drez View Post

I thought ground loop was caused by a potential difference between ground points?  EG. connecting a computer at one wall outlet to an amplifier at another wall outlet?  Have you had this sort of ground loop happen to you before?

 

Since the ground paths in the PC have non-zero impedance, and significant currents are flowing from the CPU, GPU, and other devices, there is indeed a voltage difference between different "ground" points of the same machine. If you do not believe, try doing a loopback test of a sound card with its own A/D, and then that of another card in the same PC. If the DAC and ADC are not on the same card, the noise levels are usually much worse. You can see that effect on the following graphs. Notice the large amounts of digital "crud" picked up in the D1->STX and STX->D1 tests:

 

Xonar D1 D/A to Xonar D1 vs. STX A/D:
d1_d1.png    d1_stx.png

Xonar STX D/A to Xonar D1 vs. STX A/D:

stx_d1.png    stx_stx.png

 

With sufficiently low load impedances and/or sensitive testing, effects on the distortion can also be shown. Ignoring/not understanding this problem is a common mistake in RMAA/sound card based measurements.

 

It is likely that in the USB DAC to sound card test linked above the amount of noise voltage that ends up in the audio signal depends on the impedance of the USB cable relative to that of the audio loopback cable, explaining the small variation in the results. Therefore, the test results are not relevant to typical real usage when there is no loopback cable.

post #2887 of 4002

^ very interesting - so the lower graph is using STX DAC and D1 ADC?  Guess this does represent quite a problem for sound card based measurements such as the one linked before.  Thanks for the info.

post #2888 of 4002
Quote:
Originally Posted by drez View Post

^ very interesting - so the lower graph is using STX DAC and D1 ADC?

 

Yes, it is the lower left one, while the upper right is D1 DAC and STX ADC.

post #2889 of 4002
Quote:
Originally Posted by stv014 View Post

 

I think tim3320070 meant distortions that only appear with some cables, but not others.

 

In any case, I am not sure how much useful/reliable/repeatable these graphs are. Other than the usual limitations of RMAA, they seem to have been made by a loopback from the USB DAC to an internal sound card in the same computer. This likely created a ground loop between the USB port and the input of the sound card (something that does not happen under normal usage conditions of the USB DAC), and variations in the noise floor could have been related to that.

I made these "measurments", it´s my blog someone was referring to.

 

I made it clear from the beginning of my blog that my "measurments" should be taken with a grain of salt at best; of course the RMAA plots are nothing more than nice pictures. Needless to say that I repeated these "measurments" five times each - no change so I just took one of the several plots. Furthermore, after I published the article someone else pointed out that the effects I could see were created by a ground loop. Very likely from what I´ve read about it. I was planning to do a third article on USB cables but I was delayed, I don´t know when it´ll come out. 

 

Yes, I used a loop from the Creative Soundblaster USB HD to my ASUS Xonar Essence ST, both connected/inside the same PC.

 

But I´m interested: noise was reduced when I reduced the number of devices connected to one particular internal (on mainboard) USB hub, the same to which the Creative was connected. But why? What´s the reason?

post #2890 of 4002
Quote:

Originally Posted by Marlene View Post

 

noise was reduced when I reduced the number of devices connected to one particular internal (on mainboard) USB hub, the same to which the Creative was connected. But why? What´s the reason?

 

Hi Marlene, mostly coz they acted as extra antennae catching interferences....tin-foil hat audiophiles even unplug their keyboards because of this: http://cicsmemoryplayer.com/index.php?n=CMP.ApdxAAssembly

Quote:
Remove superfluous cables from the case as they act as antennae and can cause RF interference. Disconnect the keyboard if possible.

 

Personally, I tried to use a 12V laptop brick to feed all the fans but I didn't like it...I guess this nasty SMPS was throwing more noise into the mains than I expected ^^

post #2891 of 4002

Guys, do any of you use the Tentlabs XO clock?

i'd like to know what to do with the ferrite bead that came with it.

post #2892 of 4002

Since I might have a wrong BNC adaptor, I spent a little money to buy these two adaptor to have a try.

 

Tyco Electronics

http://hongkong01.rs-online.com/web/p/products/394-0838/

 

Telegartner

http://hongkong01.rs-online.com/web/p/products/112-1833/

 

The Tyco is all plated with silver, while the other one is gold-plated brass in the contact.

 

The Telegartner is made in Germany, I like it before I buy it because German made stuff are of very good quality in my opinion. The build quality is definitely better than the Tyco which is made in Taiwan.

 

I think both of them are way better than my unknown cheap one and they also being better than the Audiophilleo bundled BNC to BNC adaptor. Anyway, I am glad that I bought them.

post #2893 of 4002
Quote:
Originally Posted by leeperry View Post

 

Hi Marlene, mostly coz they acted as extra antennae catching interferences....tin-foil hat audiophiles even unplug their keyboards because of this: http://cicsmemoryplayer.com/index.php?n=CMP.ApdxAAssembly

 

Personally, I tried to use a 12V laptop brick to feed all the fans but I didn't like it...I guess this nasty SMPS was throwing more noise into the mains than I expected ^^

All right, I guessed that this could be a reason but I didn´t know. Instead of unplugging everything (would be pointless with a PC, wouldn´t it?^^) I just bought a new USB bracket for an unused hub on the mainboard. That solved most of it, the rest isn´t important.

post #2894 of 4002
Quote:
Originally Posted by Pacha View Post

 

Please read this post I wrote quite a while ago : http://www.head-fi.org/t/446375/usb-24-192khz-m2tech-hiface/1800#post_6972839

 

At the moment I use a Viablue adapter which sounds better to me than the two others mentionned in the post above. It is 24K gold-plated, dielectric seems to be teflon. It's longer and much heavier and looks far less cheap than the two others.

http://hpics.li/19c45f2

 

It was a bit hard to find it on the web but if you consider it, here's a link to buy it (more or less 6€ for a set of two pieces, I couldn't find somebody selling only one and I think this hasn't changed since then) :

http://cgi.ebay.fr/2-Stk-ViaBlue-XS-RCA-Adapter-Cinchadapter-male-male-High-End-vergoldet-/330731622029?pt=DE_Computing_Audiokabel_Adapter&hash=item4d01240e8d#ht_2723wt_899

Hi Pacha, many thanks for the tip!

 

I have bought the ViaBlue RCA adapter. The sound is different and I tend to believe that it is better - highs are cleaner and extended. It is a strange experience because I previously swapped two different BNC cables (Canare and Blue Jeans) and it seems that the RCA adapter is better. I recommend this inexpensive experiment to everyone!


Edited by seaice - 5/25/12 at 9:43am
post #2895 of 4002

Hey. You're welcome.

 

I'm glad you also found that one can improve a setup by using a $5 adapter instead of using expensive digital cables and that they can sell these and refund themselves after having spent a lot for nothing. Again, I know some people won't have enough space to use that trick, but it's worth it when you can.

It's not even talking about the adapter being a lot better (even if I felt an slight improvement also over an Oyaide priced at around $250), it's just that it's 5 bucks VS usually much more for the same performance if not better. Definitely cheap and worth a try.

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