Unfortunately I don't have the effect nor the trust/motivation to acquire and test it myself even as a demo version.
Well... my advice is to avoid using the wide band you suggested because we have absolutely no idea what effect if any the bandwidth might have on the underlying parameters.
Try instead using some "default" settings, does the effect have presets? Whatever the plug-in initializes with in a new instance after install should be fine. Send in plain sines at the center frequency and edges of each band, noting the different results you get if any on the spectrum.
Try to normalize the result and use a proper normalized analyzer. By sending in a 0 dB sine you should get a plot where the window is normalized and the peak is 0 dB, not -12 dB or similar like your graphs are showing which would probably be the result of the tool you're using failing to bother to do any of the steps necessary to get proper results.
For authors of such plug-ins and tools, for the love of... please just implement the most basic features like normalization of your windows. The normalized window is window * 1/mean(window), it really couldn't be any more simple! When computing the fourier transform you must normalize the magnitude
by: 2/bins! It couldn't get any more simple.
(I should really make a plug-in tool some day rather than wasting my time complaining toward deaf ears... This plot is with a Kaiser window: it approximates Dolph-Chebyshev's main lobe width but has a very steep roll-off instead of a flat one.)
Ensure you're using a proper window like Hann (raised cosine) as other windows (Blackman, etc) have numerous issues, side-bands and wide main lobes with poor resolution. Blackman-Harris-b is a reasonable compromise although it will rarely be present, Dolph-Chebyshev or Kaiser as an approximation to D-C are better.
You could use a AGC plug-in with slow settings on the output from "Vitamin" before the analysis tool to ensure the input to the tool is normalized. Also test the AGC plug-in to ensure it doesn't introduce any harmonics or other content on its own. AGC with zero distortion is a trivial thing to accomplish, worst case if you can't find a plug-in to do it for you you'll just have to trim the gain each time using a simple gain plug-in instead.
You can trim the gain to get a perfect 0 dB peak output on the analyzer so the results you're seeing make sense. What you want to be measuring is the difference in levels
, not the absolute levels which don't matter at all.
Each measurement, record the gain compensation (+15 dB for example) and the spectrum graph. I'd name the screenshot (does your spectrum tool take screenshots for you?) with this information.
Example: Vitamin spectrum, default preset, sine input, 1kHz, 15 dB.png
- Plain pure sine input at various gains (-100 dB to +40 dB in 20 dB steps) and frequencies (the center and near the edge of each band.)
- AM modulated sines by sines, modulated at 1/10th Hz, 1 Hz, 2 Hz, 5 Hz, 10 Hz, 20 Hz, 50 Hz, 100 Hz.
- FM modulated sines by sines (same frequencies for modulation)
- The same of each with DC offsets added, note any differences and if none don't bother to record with offsets
So you need to iterate through a few steps with a few different test plug-ins to get a base-line response. Other tests include amplitude sweeps, frequency sweeps, varied waveforms (sine, cubic parabola(1/N^3), triangle(1/N^2), square(1/N), ramp(1/N), noise (brown, red, pink, white, gray/slate, blue) and impulse response.
As I said I doubt this will get you much further, but that's a good place to start. There really should be a VST plug-in to automate this entire series of tests and incorporate all these tools but I'm not aware of one. (...and too lazy to ever bother completing one.)
I've been thinking of creating my own spectrum + transient graph plug-in as most plug-ins seem aimed at real-time output, while that's really for the most part useless to do any proper analysis.
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