Main class and namespace in which it is declared share the same name.

namespace Spectrogram
{
    public class Spectrogram
    {
...

This causes some inconvenience when creating an instance.

using Spectrogram;

var spec = new Spectrogram(...);
// CS0118: 'Spectrogram' is a namespace but is used like a type

I know this is a breaking change, but have you considered changing the namespace's name?