The sound spectra of the Viol di Gamba 8′ and the sharp tuned Viol Celeste 8′. The frequency shift is exaggerated in the diagram to facilitate the clear separation of the peaks of both ranks. Only the steady part of the sound spectra has been utilised to extract the frequencies with an averaging time of 10 s. In the corresponding recording (3), the note C₅ is played first on the Viol di Gamba 8′, then on the Celeste rank alone and finally on both ranks yielding 1.94 Hz beat frequency. The beats with a frequency of 3.88 Hz are the result of interference between the second partials.