The role of formant positions and micro-modulations in blending and partial masking of musical instruments.

In experiments about the distinction of instruments playing in unison, it has been shown that timbres with overlapping formant areas are blending homogeneously whereas timbres with different formant areas are distinguishable very well (Reuter, 1996). On the other hand timbre separation is enhanced by micro-modulations and vibratos [e.g., McAdams (1982); Reuter (2007)]. The aim of this contribution is to find out to what extent timbre separation is influenced by different micro-modulations/vibratos versus different formant positions. 30 subjects listened to scale fragments of simultaneous playing instruments with equivalent formant areas and with different formant areas, with and without starting/ending transients, and with and without vibratos/micro-modulations. They had to answer the following question: Do you hear one sole instrument (or two of the same instruments) or do you hear two different instruments? In almost all cases featuring equivalent formant areas most of the subjects perceived one blending timbre, independent of the presence of vibratos/micro-modulations and transients. In the presence of vibratos/micro-modulations, differing formant areas predominantly led to the perception of two different timbres. Without vibratos/micro-modulations, timbre separation is much worse. These observations are explainable by a psycho-acoustical model of timbre perception.