I’ve never tried that plug-in.
Why are the tones from the Expression generator distorted?
It’s not actually distortion. It’s analyzing the normal harmonics of a square wave. If you feed a square wave into your amplifier and you get a square wave out, that’s not distortion. If you feed a sine wave in and you get a square wave out, that’s distortion.
With a sine wave it should report less distortion but there may be some distortion from sampling/quantizing as well as some "calculation/analysis error. For example, if you look at the spectrum of a sine wave in Audacity you don’t see a straight-thin line as you’d expect.
Audacity, in the bottom left, there is a list of sample rates. Are these coming from my audio card or are these
the ones Audacity can deal with?
If you’re generating tones in Audacity, It’s all “mathematical”.
When you record & play back with your soundcard you usually can’t tell. The drivers will automatically-secretly re-sample if you choose a sample rate that’s not actually supported by the hardware. It’s like printing a high resolution image on a low resolution printer your printer… You don’t get a warning that the resolution is being reduced.
I guess I could use this script to measure vacuum tube audio amps. Is that correct?
I don’t know. I’d be surprised if it can accurately measure low enough for a properly operating amplifier (let’s say 1% distortion or less).