Open the file in LibreOffice Calc (Excel should work too but I will not explain how to use it as I don't have it). I've been using and I just open the JSON with Wordpad, copy all the text, paste it into the box, click the big green download button and save the. Use a JSON to CSV converter to convert the JSON file to CSV. Click download and select your location for it. Use the lowest X and Y values you can which can successfully generate a one dot thick line covering the whole measurement. If the result is multiple dots thick, raise the X and Y values under algorithm and click Run again. You want the result to be a single line of dots covering the measurement line. Trace over the measurement line with the pen, making sure you cover all of it. The thinner the stroke you use, the more precise your generated data can be. Adjust the stroke width to the thinnest you're comfortable using. Click the color box next to foreground color. Amplitude will probably not be in a log scale, so leave log scale unchecked for Y-axis. Frequency will probably be in a log scale, so click log scale for X-axis. Click complete after adding the four points. Click proceed and follow the directions just given. Follow its directions, and note the frequency and amplitude values you click on. A diagram will pop up instructing you what to do next. Select 2D (X-Y) Plot and click Align Axes. Go to File => Load Image and load your measurement.
