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Topic: HD600 - Asus Xonar U7 vs. SB Omni Surround (Read 17975 times) previous topic - next topic
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HD600 - Asus Xonar U7 vs. SB Omni Surround

I've recently bought Sennheiser HD600 and I also bought an Asus Xonar U7 USB sound card  to have a high quality portable source for it. I also own a Sound Blaster Omni Surround 5.1 USB sound card which I use at work (the PCs have terrible on-board audio).

I was curious to compare the two sound cards - how well would they drive the HD600.
So I've bought an Y jack splitter, downloaded RMAA and started testing (using my MSI GE60 laptop running off battery, WiFi disabled). The first "problem" I encountered was that the only usable line-in was the SB Omni's one. The laptop and the U7 have only a microphone input and I was not going to risk it and connect an amplified headphone output to a 5V phantom-powered mic input (i.e. two voltage sources against each other). Amplifiers should have an output capacitor in series which should cut off the DC phatnom voltage but I'm not an audio specialist and I don't know if it's safe.

So the tests I ran were:
1) Xonar U7 headphone out - splitter - Omni's line-in and HD600 in parallel
2) Omni headphone out - splitter - Omni's line-in and HD600 in parallel
3) Laptop's Realtek headphone out - splitter - Omni's line-in and HD600 in parallel (this was unplanned, did it just for fun)

All cards were set to 48kHz/24 bit in windows playback device options (and recording for Omni's line-in), all effects disabled.

Setup 1)
Setup 2)
(How on earth do I show pictures uploaded to HA directly? It tells me "Sorry, dynamic pages in the [IMG] tags are not allowed")

I didn't take a picture of the Realtek test - I just plugged the jack into the laptop headphone output.

The results are quite surprising:
http://www.hydrogenaud.io/forums/index.php?showtopic=107821

Screenshot

I did not perfectly level-match the 3 cards. However, I set both U7 and Omni very close to each other. Xonar U7 was set to highest of the 3 amp levels and windows volume at 74%, Omni - having a more powerful amp - was set to 56% and Realtek was set to 90% (a bit louder than the other two, maybe giving it a bit of advantage on the SNR test).

Quite unexpectedly, Xonar U7 was only marginally better than the Realtek. Omni ended up a class or two above both.

Normally, people RMAA loopback of a single card. In the above scenario, the only difference was the source (output). The input was always the same with the same settings (I just switched the black cable to a different output and selected that output in RMAA). The only explanation I can think of (besides Xonar U7 being a very mediocre product) is that there was some grounding issue between the two cards (I tried swapping the devices between various USB ports on my laptop which had no effect on the results). Or is there some other reason why analogue loopback on the same card should have such huge advantage? I mean if Omni could feed it with such a good SNR why couldn't U7?


I did not test any lower-impedance headphone because the output level I needed for line-in would have fried it (Omni's line in was set to 100% volume). Even the HD600 was painfully loud at that volume (the RMAA test is not very pleasant to listen to, anyway  )

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #1
Out of curiosity, I also tested my portable players (see the uploads thread). They both seem to beat the U7 except for the L/R crosstalk where they suck. I had to do it at 44/16 because the players produced atrocious resampling artifacts for 48kHz input.

Note that I do not claim to be able to hear any of the differences I measured.

I will try to figure out how to test with low-impedance headphones (without having to blast them with ridiculous voltage). I expect all the measured devices to perform significantly worse with e.g. 16 ohm headphones.

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #2
Set the clip to 48k output if you want to test 48k files.

I wouldn't be surprised if the xonar is mediocre. A lot of those USB sound cards are pretty bad.

You shouldn't have a problem driving most headphones at line level voltage or maybe a little low if you want to be safe.

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #3
The Xonar U7 headphone amp is mediocre at best, or at least it seems that people on Headfi think so
IIRC it has a pretty high output impedance and can't power hungry headphones, though it should have pretty good specs as a DAC, unfortunately there's few measurements done on that card, only a few RMAA in PC gaming websites and a test done by a guy who uses the card for SDR, though those are for the ADC

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #4
Well, that sucks. I mean U7 is twice as expensive compared to the Clip+ and considerably more expensive than the SB Omni, yet they fail to equip it with a low noise quality headphone amp circuit?

Taken from their U7 marketing material http://www.asus.com/Sound_Cards/Xonar_U7/
Quote
Integrated headphone amplifier pumps up every sound detail

Quote
Xonar teams integrate a headphone amplifier on Xonar U7 to boost immersive headphone output.


The above sure does not seem to imply that U7 is no better than an on-board Realtek when it comes to driving headphones... Deceitful bastards.

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #5
You really shouldn't buy an amp or DAC without actually verifying that the specs are good.

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #6
The Xonar U7 headphone amp is mediocre at best, or at least it seems that people on Headfi think so
IIRC it has a pretty high output impedance and can't power hungry headphones, though it should have pretty good specs as a DAC, unfortunately there's few measurements done on that card, only a few RMAA in PC gaming websites and a test done by a guy who uses the card for SDR, though those are for the ADC



This one paints a pretty good picture:

Xonar U7 Review

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #7
I did my best before buying it. I have no idea how the reviews measured the sound card to achieve those numbers (I can only guess it was line-out to line-in). Also the last two charts in the review Arnold linked look quite suspicious, especially the crosstalk. Why would the line-out have a worse cross-talk than the headphone-out? It does not make any sense to me.

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #8
I did my best before buying it. I have no idea how the reviews measured the sound card to achieve those numbers (I can only guess it was line-out to line-in).


I believe that the tests are exactly based on on line-in to line-out.  They are indications of the performance of the card in that mode of operation, but they would require additional tests with simulated or real headphone loads to be relevant to that mode of operation.

Quote
Also the last two charts in the review Arnold linked look quite suspicious, especially the crosstalk. Why would the line-out have a worse cross-talk than the headphone-out? It does not make any sense to me.


Most crosstalk is due to signal leakage between the channels, which is often greatest when higher impedances and higher frequencies are involved. Thus one need not be concerned when the testing of a higher impedance output shows e more high frequency cross-bleed than that of a lower impedance output.

I don't think that many people have actually done listening test to determine requirements for controlling cross-bleed or crosstalk in order to avoid undesirable alterations to the sonic scene.  Its been a long time since I did any such thing, but my recollections is that someplace between 20 and 40 dB separation, audible alterations of the sonic scene vanish.  IOW 60 or 80 dB separation are just two different numeric permutations of sonically perfect performance.

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #9
The tests in that link are unloaded tests and so not very useful unless one is also planning on buying another amp. Of course if you were going to do that I'd suggest that you buy an amp with a quality DAC built in ; )

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #10
The tests in that link are unloaded tests and so not very useful unless one is also planning on buying another amp. Of course if you were going to do that I'd suggest that you buy an amp with a quality DAC built in ; )


I see the possibility of using a good inexpensive headphone amp such as the Topping NX1 to address this audio interfaces weak performance with low impedance headphones.

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #11
The tests in that link are unloaded tests and so not very useful unless one is also planning on buying another amp. Of course if you were going to do that I'd suggest that you buy an amp with a quality DAC built in ; )


I see the possibility of using a good inexpensive headphone amp such as the Topping NX1 to address this audio interfaces weak performance with low impedance headphones.


That would absolutely work, but for what they charge I'd expect a quality amp built in.  Fiio will sell you that for the same price for instance.  Not like these things are expensive or difficult.

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #12
The point was having only a single piece of hardware. Maybe I'm a stupid or something but I did not really expect a soundcard with a built-in headphone amp to be so much different from a headphone amp with a built-in DAC.
At least not at that price point. Or does common sense no longer apply today?

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #13
I have no idea how the reviews measured the sound card to achieve those numbers


  • you need the highest quality ADC that you can get your hands on;
  • when trying to measure the SNR of a device, you need to do it unloaded, and set its volume to the maximum (and the ADC needs to be able to record it without clipping);
  • when doing the measurements with headphones attached, you need to set the volume to a "loud" level that won't make you insta-deaf and that won't significantly raise distortion figures. The measured SNR will be lower, but you already measured it with the unloaded test.


I see the possibility of using a good inexpensive headphone amp such as the Topping NX1 to address this audio interfaces weak performance with low impedance headphones.


That would absolutely work, but for what they charge I'd expect a quality amp built in.  Fiio will sell you that for the same price for instance.  Not like these things are expensive or difficult.


I haven't seen any evidence so far that the headphone amplifier in the Xonar U7 is bad.

I did not really expect a soundcard with a built-in headphone amp to be so much different from a headphone amp with a built-in DAC.


They are the same thing.

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #14
I haven't seen any evidence so far that the headphone amplifier in the Xonar U7 is bad.


I'm under the impression that it provides a source impedance that may be too high for really low-impedance headphones. The number 10 ohms seems to be rattling around in my head.

The online spec sheet says: Headphone output : 1.3 Vrms (3.677 Vp-p)  which is a little low for some really high impedance headphones resting on ears who like it loud.

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #15
I was apparently interested in a loaded headphone-out SNR figure since this was what I was going to use. I didn't need a high quality ADC, just ADC with figures better than what I was measuring. The U7's headphone output was "so bad" that SB Omni's line-in was good enough.

Every device I have used was able to drive HD600 at a volume higher than what I needed.

Just look at my measurements, there you have evidence that for HD600, this sound card is no better than the laptop's integrated Realtek.

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #16
I was apparently interested in a loaded headphone-out SNR figure since this was what I was going to use. I didn't need a high quality ADC, just ADC with figures better than what I was measuring. The U7's headphone output was "so bad" that SB Omni's line-in was good enough.

Every device I have used was able to drive HD600 at a volume higher than what I needed.

Just look at my measurements, there you have evidence that for HD600, this sound card is no better than the laptop's integrated Realtek.



The presence or absence of a headphone load is unlikely to materially affect SNR.

The presence of a load might affect THD or more importantly FR.

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #17
The SNR in rmaa usually does depend on load because it plays a tone and measures the noise floor. Thd and other effects end up factored into the noise.

Although looking at this test:
http://rmaa.dfkt.tk/Comparisons/Comparison...600%20Loads.htm

The entire noise floor seems to rise with increasing load. Maybe more power supply noise is coupled in at higher currents?

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #18
The SNR in rmaa usually does depend on load because it plays a tone and measures the noise floor. Thd and other effects end up factored into the noise.

Although looking at this test:
http://rmaa.dfkt.tk/Comparisons/Comparison...600%20Loads.htm

The entire noise floor seems to rise with increasing load. Maybe more power supply noise is coupled in at higher currents?


Power supply noise could have something to do with the increased noise. Noise from the power supply sometimes tends to increase when the amplifier is pretty heavily loaded.

What was the power source - batteries, a wall wart, or other?

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #19
Cowon D2 is an old mp3 player, so its battery powered.

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #20
Cowon D2 is an old mp3 player, so its battery powered.



Well, that may explain why the increase in noise seems to have taken the form of random noise. If it was powered by the power line the usual situation is that the increased noise while driving low impedances has strong components related to either the power line or the operational frequency of any switchmode power supply. When you put a heavy drain on batteries you increase chemical activity which may create more random noise.


HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #22
I intentionally ran the test on battery power. Maybe there is another source of power noise in the laptop (it's a powerful gaming laptop). Anyway, components in the less expensive SB Omni had absolutely no problems with noise so why couldn't U7...

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #23
Setups 1) and 3) show copious amounts of what looks to be ground loop noise spoiling the results. Not sure why the Omni is better here - maybe someone bothered to implement an (electronically) balanced input? USB port in a different location vs. U7? Some custom cabling to break the loop should fix that if need be.

IMD on the Realtek also indicates that it could use a driver update (should be 2011, early 2012 vintage now). Should be similar to U7 then, except still higher in output impedance / FR deviation.

HD600 - Asus Xonar U7 vs. SB Omni Surround

Reply #24
I see the possibility of using a good inexpensive headphone amp such as the Topping NX1 to address this audio interfaces weak performance with low impedance headphones.


That would absolutely work, but for what they charge I'd expect a quality amp built in.  Fiio will sell you that for the same price for instance.  Not like these things are expensive or difficult.


I haven't seen any evidence so far that the headphone amplifier in the Xonar U7 is bad.


I measured a source impedance of 17 ohms on mine, and that makes it iffy for low impedance 'phones.

 
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