AudioSpectrum.cs

// We can perform an FFT on the microphone data...
var device = ... as AudioDevice;
// Using an audio spectrum output...
var spectrumOutput = new AudioSpectrumOutput();
// But we can also do more with the audio data...
device.StartRunning(audioBuffer => {
    // Update the spectrum output
    spectrumOutput.Update(audioBuffer);
    // But do other stuff with the audio buffer
    DoOtherStuff(audioBuffer);
});