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Old 21st February 2012, 12:41 AM   #21
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New results with ARTA, 991Hz signal. "THD+N" is the DCD-360 (4562 OpAmps) at -0.6dB. "Null" is with the CD player stopped (noise?). DVD-2931 is the PCM1791 with AD8599 OpAmps one. "DCD360" one is at -3dB. Last one is loopback on my X-Fi Platinum bay.
Gosh, 0.011% that's way better! I still suspect a limitation due to my ADC - at some 0.01% now...
Attached Images
File Type: jpg thd+N.JPG (118.7 KB, 90 views)
File Type: jpg null.JPG (120.5 KB, 84 views)
File Type: jpg DVD-2931.JPG (121.1 KB, 81 views)
File Type: jpg dcd-360.JPG (119.2 KB, 78 views)
File Type: jpg loopback_Platinum.JPG (121.7 KB, 76 views)

Last edited by SoNic_real_one; 21st February 2012 at 01:10 AM.
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Old 21st February 2012, 02:47 AM   #22
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Did you label those graphs correctly? The loopback looks terrible if it really is the last graph.
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Old 21st February 2012, 10:32 AM   #23
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Yeah, I know! I have used an Y adaptor from 3.5mm jack (back line out) to RCA (front bay input cables). I wonder if that made it look that bad...
Players are connected RCA-RCA. On front bay I have as output a headphones jack (1/4" type).
Or maybe this how 44.1kHz looks on the output of X-Fi...? The input I think it does not go tru the DSP so it might be "cleaner". I'll try with different frequency settings when I will come back from work.

Last edited by SoNic_real_one; 21st February 2012 at 10:40 AM.
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Old 21st February 2012, 04:35 PM   #24
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Well it's clear that the sound cards performance is dominating the measurements. It is possible that some DSP processing is going on somewhere though. Do you know what ADC the X-fi uses?

Using a Y splitter shouldn't make things that much worse.

You mention that the X-fi uses a drive bay to the front of the PC. Does the drive bay contain the DAC/ADC or does the PCI card at the back have them on and then its wires to the front? If its wires to the front, if they are transferring analogue signals then they could be picking up lots of noise. A friend once had awful noise issues when using the microphone socket on the front panel, now obviously a lot of gain was applied afterwards, but we are talking about trying to measure low distortion here, so it's just something to think about.
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Old 21st February 2012, 04:56 PM   #25
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I will take a look inside the bay tonight. The bay has independet ADC and DAC and is connected via SPDIF lines (inside a 40 pin IDE cable) to the PCI card. X-Fi has one more ADC on PCI board itself, but input is via 3.5mm jack. Some say that ADC is WM8775SEDS.
About DSP - maybe the Crystalizer was "on" or something stupid like that. Will check that too.
Click the image to open in full size.

Last edited by SoNic_real_one; 21st February 2012 at 05:04 PM.
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Old 21st February 2012, 09:22 PM   #26
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That ADC should be capable to 0.003% and is roughly in line with the performance of the PCM61. Of course the surrounding analogue stuff can ruin that performance.

If possible I would use the 3.5mm input jack on the sound card itself. At least just as a test to see if the drive bay is the real issue.
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Old 21st February 2012, 10:24 PM   #27
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Thanks for the ideas. This is the PCM61 using the X-Fi card input (ADC). Worse than the bay input. But granted, second harmonic is way lower.
I wonder if I can improve the input on the bay...
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File Type: jpg PCM61P-internal XFi.JPG (122.2 KB, 24 views)
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Old 21st February 2012, 10:38 PM   #28
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Something looks wrong. The DAC should only produce harmonics at 2k 3k 4k etc. but there is lots of spurious in between.
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Old 22nd February 2012, 12:13 AM   #29
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Well, those might be from the ADC?
My X-Fi bay DAC is CS4392, digital receiver for DAC is CS8415A. I cannot figure the ADC - I think is a Philips one, but can't make out the numbers. Can it be UDA1361T??? That has THD+N= -88dB at level -1dB and -40dB at level -60dB.

I did burn a CD with -60db level and I did rotate all the DAC's that I have in one socket. Good news - all worked. Bad news - all had THD between 1% and 0.61%. I was able to "select" from all 8, two with lowest THD. This based on my limited ADC means almost nothing. Time to get a E-MU1212...
Attached Images
File Type: jpg PCM61_-60db.JPG (122.5 KB, 16 views)
File Type: jpg ADC.JPG (500.1 KB, 13 views)
File Type: jpg ADC_1.JPG (510.0 KB, 14 views)
File Type: jpg DAC.jpg (338.3 KB, 16 views)

Last edited by SoNic_real_one; 22nd February 2012 at 12:39 AM.
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Old 22nd February 2012, 12:54 AM   #30
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Bah creative and their flashy pieces of junk ;/ Even the cheapest card in Asus' Xonar range 20-30 beats that from chip specs.

The next up, the Xonar DX at around 50 uses this ADC

http://www.cirrus.com/en/pubs/proDat.../CS5361_F2.pdf

And a quick look at some reviews has it performing pretty much to spec.

Asus' Xonar DX sound card - The Tech Report - Page 1
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