Balanced Soundcard Interface for Power Amplifier Distortion Measurement - Page 2 - diyAudio
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Old 24th October 2011, 10:45 AM   #11
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From wat i understand, the oscillator in this thread makes for a very good investment if youare doing a lot of testing. It is based on AN-67.

DIY Analog-to-Digital Converter project.Audio measurements tool

Here is thrread with more info

LT AN67 Ultralow THD 10kHz sine oscillator group buy.

Last edited by buzzforb; 24th October 2011 at 10:50 AM.
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Old 25th October 2011, 06:32 PM   #12
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Dave,
If you go with the Tascam usb sound card let me know how it works out, I am out of slots on my workbench PC so a external box is the way I need to go.
Thanks
Bill
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Old 11th December 2011, 09:11 AM   #13
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Question if I may: is anyone of you using their soundcard with W7 64bit? I have an older EMU 0404 external soundcard box, but can't get it to run under W7 64bit. Several forums document this; EMU does have a beta driver for W7 64bit but it seems to work for some, not for others, without clear info why.
Maybe I should get another like the M-Audio 192kHz, but would like to be sure that it would run under W7 64bit.
BTW I have a license for ARTA/STEPS.

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Old 11th December 2011, 11:25 AM   #14
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I have read that Juli@ and Asus Xonar cards are best in field when it comes to updated drivers. I plan to purchase Juli@ card as it seems to offer greatest balance in terms of features and performance.
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Old 23rd June 2012, 05:21 PM   #15
kouiky is offline kouiky  United States
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The salient question that may be poised by members at this stage is how much distortion was truly superimposed by the testing apparatus (IO soundcard & DAC) over the amplifier being tested, and how do we compensate for it because there are several values shown? Another member tried this method and found much different results. The measured values vary from that on the CDM accordingly to each device's own distortion character and order proportions and final interference of each. How would each compare to that shown on reliable scientific calibrated outboard spectrum analyzers that properly compensate for the test probes signal reduction? From what I'm seeing, the data displayed using this sound card method is prone to error and difficult to interpret without proper calibration. So, how should users actually interpret the results for their own perusal?

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Old 23rd June 2012, 06:07 PM   #16
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The PreSonus cards aren't working well (yet) under 64 bit windoze. Might pay to be careful if considering that.
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Old 23rd June 2012, 06:26 PM   #17
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Kouiky:

By doing loopback tests of the M-Audio AP-192 I found that noise and distortion was much reduced using balanced outputs and inputs rather than unbalanced. My impression is that until amplifier being tested (DUT) has noise and distortion levels approaching those of the soundcard, the soundcard can be largely ignored.

Since the soundcard interface presented here is only intended for measurements of the low impedance amplifier output (usually 8 ohms or less), and is of a totally resistive nature, there should be no calibration issue other than overall signal level. It you accurately know the resistor divider and the soundcard levels you should be good, otherwise you need to calibrate by some means. For THD measurement, the absolute signal level accuracy is less important than the ratios of harmonic levels to fundamental.
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Old 24th June 2012, 02:28 PM   #18
kouiky is offline kouiky  United States
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This is a good read from a BSEE who worked in the audio industry for years. It's good for anyone trying to test equipment via USB, soundcard and freeware and explains the limitations of reliability due to unseen interactions within a computer that the software and card can't account for and common errors. Interestingly, it appears many audio manufacturers still print erroneous performance results because they are using these methods. He tested a company's product and after the manufacturer saw his results, they used his values! The high end manufacturer didn't even have test equipment and their headphone amp almost destroyed the headphones.
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Last edited by kouiky; 24th June 2012 at 02:31 PM.
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Old 24th June 2012, 03:21 PM   #19
Pano is offline Pano  United States
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Thanks for the link, a very detailed analysis of RMAA. I prefer Visual Analyzer for most measurements. or ARTA. But the problems of soundcard related measurements still remain.
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Old 24th June 2012, 03:24 PM   #20
lhquam is offline lhquam  United States
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Very good article. Thanks for posting it. I totally agree that the use of PC soundcard based testing is error prone and must be done carefully and with an understanding the the potential problems and limitations.

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Originally Posted by kouiky View Post
This is a good read from a BSEE who worked in the audio industry for years. It's good for anyone trying to test equipment via USB, soundcard and freeware and explains the limitations of reliability due to unseen interactions within a computer that the software and card can't account for and common errors. Interestingly, it appears many audio manufacturers still print erroneous performance results because they are using these methods. He tested a company's product and after the manufacturer saw his results, they used his values! The high end manufacturer didn't even have test equipment and their headphone amp almost destroyed the headphones.
NwAvGuy: RightMark Audio Analyzer
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