Acoustical coupling between two guitars, onset variation, and timbre perception

Acoustical coupling between simultaneously played musical instruments has been observed at times, for instance, between adjacent organ pipes [F. Trendelenburg et al., Akustische Zeitschrift 7-20 (1938)]. The observation here concerns two guitars that reveal a different timbre when played simultaneously (A) in contrast to when played separately with the tracks being mixed afterwards (B). Alternatively, the two guitars are played separately but each with a simultaneous steady-state tone presented by a speaker while the frequency relates to the key (C). Subjects rated the music produced under the paradigms A and C as being similar and music produced under the paradigms A and B as being dissimilar, likewise for B and C. The differences were attributed to timbre. For analysis, a mechanical plugging mechanism replaces the musician on the first guitar, whereas the second guitar is replaced by a steady-state tone. While most of the partial tones remain unaffected, partial tones above 3 kHz rise more sharpely and reach higher levels during onset when a simultaneous tone is present compared to when it is absent. Although these partial tones decline rapidly and finally progress toward comparable levels with and without the simultaneous tone, the perceived timbre differs noticeably.