"Mirror QA401 Output" option level issue

in the link qa401MirrorLevelBug.wmv is the ScreenRecorder video showing the problem with output level of a DAC when the “Mirror QA401 Output on your PC” is used.
If your video player is not playing the video correctly, use Windows MediaPlayer.

The generator level setting will not catch from first, i.e. DAC output goes to max level and I have to set the level again to work properly.
The problem is much worse when any of the Test Plugin is used (see the attachment “v1.907 test.png”); all the measurements are made with max level, although “Gen 1” shows the level it suppose to be.
The problem exists in versions 1.907 and 1.908. I didn’t test extensively, but apparently versions 1.900 up to 1.906 don’t have the problem (see the attachment “v1.904 test.png”).

Hi @zoran4afc, sorry for delay as yesterday was a holiday in the US.

I will study this. One thing I note from your video is at the 1:35 mark you have -6 dB specified for the External Input Gain. If this value is anything other than zero, it will offset the measured result by the specified amount.

Looking at this more, I think there are a few things going on here:

  1. When you enable Mirroring and press run for the first time, the level hasn’t yet been set. If you then increase amplitude by one step and then reduce it by one step, the correct value is written. This happens anytime you change the level using the dlg box. (eg control click on Gen1). So, the bug to be fixed here is to ensure the updated level is set for the PC in all the code paths.

  2. For the automated test, the non-zero offset is one issue, but I think the issue identified in 1) is also coming into play

  3. I don’t like that the frequency rounding isn’t happening for remotely generated PC tones. That is also an issue that was touched on in this thread:

I’ll try to get a release addressing the 3 items above turned around in the next few days.

Thanks for reporting, Matt

Hi @zoran4afc, I think this has been hugely improved in release 1.909. Can you please try when time permits and feedback? Thanks

Hi @matt,

yes, the mirror levels are now applied, thank you!
Also, the Frequency Response graph is now perfect. I thought before that the problem is with my DAC, but all external DACs measured the same.
Not only that Frequency Response plugin works perfectly, also the normal spectral analysis shows consistent levels at all frequencies in range 20Hz - 20kHz.
This is remarkable improvement!
One question: Only “Gen 1” works in the mirror mode. “Gen 2” and “Multitone” does nothing. Is that the limitation of mirror mode or bug?

Best regards

Yes, only Gen1 works in mirror mode. At some point in the future, you will be able to set FFT size, then generate a special chirp WAV in the analyzer app, and then loop that wav on your dac and the QA401 will capture it. But that’s a little ways off with some big items that need to be done first.

I am looking forward for those future features.
I hope that it will be possible to measure phase shift in mirror mode too.