Spectrogram of piano tones, illustrating harmonic equivalence (octave equivalence). From 0.00 to 1.00 seconds: piano tone with fundamental frequency 262 Hz. From 1.00 to 2.00 seconds: piano tone with fundamental of twice that frequency. From 2.00 to 3.00 seconds: these two tones sounding together. Tracing out of harmonics from each tone is apparent as horizontal bands, with brightest white bands being the most intense (loudest). The two tones sounding together have an almost identical graph as first tone.