The Note Display block is a tuner on the board. Feed it an audio signal and it shows the note being played (for example A4), a meter of how many cents sharp or flat it is, and the frequency in Hz. The needle is coloured by how close you are: in tune within 5 cents, close within 15. It has one audio input and no outputs, so it only shows and never changes what you hear; in stereo it listens to the mid of the two channels. When the note fades the last one stays on screen, dimmed, for a second. There are no parameters.
Pitch is found with the McLeod pitch method: the block keeps the last few thousand samples (two periods of 40 Hz, so a bass's low E is in range) and, four times per window, computes the normalised square difference function through an FFT-based autocorrelation. The first strong peak gives the period, refined by parabolic interpolation; picking the first rather than the highest peak is what prevents octave errors. A weak peak (noise, silence, chords) reads as no note. The frequency is named as the nearest equal-tempered note with A4 = 440 Hz. It takes one sample per tick, like every WaveWarp block.