What do C1, C2, etc. numbers in the Spectrogram mean?

[shelley]

The C1, C2, etc. numbers visible on the left of the Tabbing View refer to the octave of the note. For instance, C4 corresponds to “middle C” on the piano, and C3 would be one octave below that. There’s more information about octaves here on Wikipedia if you’re interested in learning more—https://en.wikipedia.org/wiki/Octave