QA402 Feature Request

Hi Matt,

I know this is a ways off as you are getting the standard features up and running on the new hardware.

Anyway, I was wondering if you could add a residual distortion plot to the Time Display. This would be in addition to the input waveform. So we can compare the phase of the input to the residual waveform. Nelson Pass references this on a regular basis for adjusting amplifier distortion profiles. It’s old school, like on an analog distortion analyzer.


If others are interested please let Matt know here :grinning:

Hi @Botte, the QA401 software has a menu item called “visualizers” that will be added to the QA402. There are two visualizers currently in the QA401 software, one is wow and flutter and and the other is a residual viewer. It will also be the place that amplifier dynamics will be added to let you see how a amp will handle transients. So, it’s coming

Great! :grinning::+1:

Thanks for the update

This is more a small “nit” than a feature request, but it would be nice to have the QA402 software remember the directory where it last saved the Exported Frequency Series data to. If you save a bitmap, the next time you save another bitmap it will be in the same directory (this assumes that you are in the same “session” as to when you first started your measurements). If you go to export the frequency series data (the only export I have used), it will bring you to the program’s default directory, which is not where I want the data saved, each time. Not a show stopper, but does slow things down just a tad.

May I second that.
Added this text to comply to the ‘post must be 20 or more characters’ rule :slight_smile:

Hi @VAR and @FdW, yes agree this is painful when you are exporting over and over to a non-default location. For 0.996 this will change such that the first run of the application will use the default, but subsequent exports for time and freq will remember your last saved path. And then, when you re-start the app, the first save will again go to default, and subsequent will remember your last saved path.

Painful may be to harsh a word, but am glad it will be changed in a future update…Thanks!

It would be nice to have the measurements (windows/boxes) saved and loaded when using the LOAD SETTINGS. Right now it does not appear to load them…It would be nice to have the settings state that is loaded (if one was) displayed on the bottom of the window where the USB voltage/currect etc is displayed, but that is probably very low on the list.

It would very handy to have the option of having the display show Power (into 4, 6 or 8 ohms most likely) when doing an FR, rather than dBV…

It would be nice to have the measurements (windows/boxes) saved and loaded when using the LOAD SETTINGS. Right now it does not appear to load them…

That should be in 0.996, let me know if you aren’t seeing it

It would very handy to have the option of having the display show Power (into 4, 6 or 8 ohms most likely) when doing an FR, rather than dBV…

Yes, that could be useful

I did create a spreadsheet that allows does that, but it obviously requires several more steps :smiley:

Is there a way to graph H2 and H3 in addition to the THD in the Power vs THD automated procedure?

Hi @Botte,

there is a plugin for the QA401 that graphs distortion versus level, and it lets you break out 2H and 3H. The plots look as below. Not the purple (3H) defines the overall THD. This was part of a study for looking at the balance between 2H and 3H for guitar distortion, but obviously relevant other places too.

I’ll make sure this plugin gets added to next week’s release for the QA402



This look like what I need. It would be nice if it was power and I will get the visual from this even if it’s not.


Hi @Botte, release [0.997] has the AMP Gain and Distortion versus Amplitude plugin. We’ll look at enabling it for power amps too in a later release

So, In addition to have Markers in the FR mode, and a Delta marker(s), and the ability to have power displayed in FR mode instead of dBV, would it be possible to have some more control over the Y-axis scaling? Not necessarily an “autoscale”, but the ability to manually set the upper and lower limits. Maybe there is a step size for the Y increment that I just don’t know about. For instance, the nerd in me wants to have a vertical scale of between -13 & -15dBv in the graph below:

Hi @VAR, Normally, the axis settings buttons (YMIN and YMAX) move 5 dB per click. If you press the control button while clicking, it will move 20 dB per click. And if you press the alt button while clicking, it will move 1 dB per click.

And then the Y preset buttons can be you back to two of the most common settings quickly.

Alternately, you can click and drag a box around the area of interest and you will zoom to that region.

Thanks Matt. Something told me there may have been a way to change that setting- it will save some time in the future!

So, my feature request wishlist for today is:

  1. It would be nice if you could save a bitmap that included everything that was on the QA402 Screen, so that you could have all your settings shown- keep the save bitmap there as it is, but have a “Save Fullscreen” option as well.
  2. It would be nice to be able to drag the measurement windows around on the measurement area of the screen to where you could have certain ones next to each other. I suppose you could add one measurement and then click again and add another, and add another, but I just click everything I want to see and they may or may not be displayed next to each other for easier viewing…

I will put this under Feature request, but it is more like a “nit”. When using the “zoom mode” to drag a rectangle over the traces you want to expand the resolution of the “Y” axis say, like you might when looking at an FR plot, if you get the area somewhat zoomed in on, but would like to move the Ymin/YMax axis around just a little bit more, your are not able to without it undoing the Zoom that you just got. It does not make a difference if you have the ALT Key pressed down so as to move in +/- 1dB increments- as soon as you hit a Y axis up or down arrow it zooms back out…