QA40x notes, findings and feature requests

1

I have my QA403 for a few months now, and I just wanted to share what came to my attention and what I have written in my notepad during measurement sessions. I use it mostly in my home lab and occasionally professionally. Besides I also have access to Audio Precision, Klippel, Head acoustics stuff, giga-samples oscilloscopes, Rohde&Schwarz stuff… I mostly prefer the QA due to its size, portability and speed of use. It gets the 93.5% of the jobs done (fast)!

Don’t get me wrong, I want to see the QAs strive! So these points are to be understood as suggestions for continous improvement.

QA40x SW (up to v1.193):

  • Last folder persistence for measurements. I make a lot of reports with pictures for customers. Re-selecting the current work folder is super tedious. It would be great if the last used “save bitmap” folder would be persisted.
  • Super slow response after several automated measurements. The QA SW gets super slow after some automated test runs. Very high latency then.
  • “Testing in progress window” is super upfront, blocks further work with PC. Can that be de-prioritized so I can do other stuff with my PC while an auto measurement is running?
  • “Graph tool window” closes with no “are you sure?” prompt
  • “,” instead of “.” in Graph Tool. The Graph Tool uses “,” as decimal separators. I would much prefer “.” or the option to set my preferences.
  • Window Size of QA40x not persisted shutdown. I have a 4k screen and the QA40x SW always starts with the standard size, which is quite small.
  • The QA40x SW is 32 Bit according to Windows Task Manager. Why is that?
  • Pk and fast VU meters to judge if DAC and ADC are in their “comfort zone” and for quick reference to see if a signal is acutally going out/coming in.
  • Automated Tests: Another sub level in the global menu would be great. It is cumbersome to find a specific measurement due to the wall of text. “Automated Tests” “Amp” “DAC” “Misc” and under that the actual plugins.
  • Please add a shortcut to open the Graph Tool
  • Automated Test “Dynamic Range” in accordance with AES17 would be great

QA403 HW:

  • I would love to have an headphone output on the QA40x HW. Why? I am by trade an audio engineer and the rule number 1 is: ALWAYS LISTEN TO TAPE RETURN! With measurements, no one listens into the measured signal. That makes bugfixing and sessions unnecessarily complicated and error prone. Obviously that would be needed to be limited and compressed. AP is doing quite a good on that front.
  • Power via external power supply. On the one hand it is nice that the QA403 is USB powered. But on the other, It is so power power hungry. It occupies one USB stem or I need a powered USB hub. Often, the DUT also is connected via USB. If I could have the option to power it safely externally, would be great. Maybe share the SMPS from the QA461? I prefer a SMPS over a USB hub!
2
  1. I think power via an USB external supply would be a nice option. 2) As you can play a .wav file via the QA40x- maybe for burning in something- the headphone jack monitoring the input to the QA40x would be nice and save me the work of building one into my loads 3) Remembering the last folder used when saving bitmaps would be nice. 4) A dynamic range automated test would be nice. I have yet to get into automated testing so can’t comment about that area.
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3

Hi @philipppaulklose, all excellent comments. What version are you currently using? The window size should be persisting.

What would you think of monitoring audio in via PC speakers?

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I think monitoring with PC speakers would be fine- the signal going into the QA40x would be the more important signal to monitor, I would think…

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5

I am currently on 1.202 with FW v60. The window size is not persisted after closing the App.

Output to PC via WASAPI or WASAPI exclusive would be great!

6

Hi, the window does not persist if it has been maximized with the Windows button. If you manually resize the window without getting to full screen, the window size is maintained.

7

Youre right! When I maximize via fullscreen, it does not get persisted. When I “manually” resize it gets persisted.

8

Another feature request-- my QA403 shows some residual (very low) harmonic distortion when connected output to input. Does it physically and mathematically make sense to store a calibration file similar to DC offset correction and subtract inherent distortion components for a set of frequencies?

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9

Hi @Belleson, yes, there was a guy (phofman) on DIY Audio a few years back that was working very hard on this and I think he really pushed the state of the art forward. The problem you have is you have THD contribution from the DAC and ADC that have to be detangled. As I recall, phofman used a single low-pass filter the change the phase of the DAC contribution, and then that gave him the system of equations needed to separate the DAC and ADC contributions. A really ingenious and simple (but non-obvious) approach.

Alternately, you can use a notch filter to drop the level into the ADC and pick up some benefits there too. With 30-40 dB of notch suppression you can pretty much completely isolate the DAC contribution.