FmodAudio wrapper in C#, but how to use?

I’m trying to extract spectral information using this GitHub - sunkin351/FmodAudio: C# .NET Core Wrapper for the Fmod audio library, but there is some information lacking on how to use it.
It implements the Fmod binaries and all underlying code.

I want to do something like (the params are slightly different from the official documentation, instead of 2 out params, it returns the result as a void*)

var res = fftPass.GetParameterData(index, out length)

but for the index parameter, I can’t find the [DSP::getNumParameters] object, so I am not sure what to pass in there. The result is probably(?) an IntPtr, and this result has to be converted via a Marshall.PtrToStructure(…) into a ParameterFFT object.

The block of code looks like this:

fftPass = System.CreateDSPByType(DSPType.FFT);
fftPass.Active = true;
fftPass.Bypass = true;

unsafe
{
uint length;
IntPtr unmanagedData = (IntPtr)fftPass.GetParameterData(0, out length);
ParameterFFT fftdata = (ParameterFFT) Marshal.PtrToStructure(unmanagedData, typeof(ParameterFFT));
var spectrum = fftdata.Spectrum;

}

What am I doing wrong apart from not knowing the index of the GetParameterData?
Any guidelines would be helpful, thank you.

We have some examples on using the GetParameterData() function in this script, which should help you understand it a bit better.

https://www.fmod.com/resources/documentation-unity?version=2.2&page=examples-spectrum-analysis.html