Signalizer (written by Janus Thorborg), is a freeware plug-in available in 32-bit & 64-bit VST/VST3/AU plugin formants for Windows & Mac OS.
Here's a screenshot I've just taken of a single snare hit (for James
I also use its Spectum mode to show me the harmonic contributions of preamps etc. (here's Fuse Audio's VPRE-2C plug-in in action):
Spectrum also offers a Sonogram mode, which is perfect for examining harmonics and aliasing (here's the same preamp showing how clean it is):
There's also a Vectorscope option to examine stereo phase information, which I've used extensively when examining the width & depth of chorus/flanger circuits (here's Arturia's JUN-6):
With a 1-sample length Dirac pulse as the input signal (freely available online) Signalizer's variable persistance trace means that you can capture stereo frequency responses (this is True Iron):
It's fully resizable (vector-based graphics), and also offers a full-screen display option when you really need to examine and measure something more closely. Yes, with this number of options it can be confusing at first, but I've built up my own collection of presets during heavy use.
Download it here: https://www.jthorborg.com/index.html?ipage=signalizer
HIGHLY recommended for all PC and Mac users!!
Martin