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What is the relationship between a musician-designer's auditory imagery for a musical piece, a design idea for an augmented instrument to support the realisation of that piece, and the aspiration to introduce the resulting instrument to a community of likeminded performers? We explore this NIME topic in the context of building the first iteration of an augmented acoustic guitar prototype for percussive fingerstyle guitarists. The first author, himself a percussive fingerstyle player, started the project of an augmented guitar with expectations and assumptions made around his own playing style, and in particular around the arrangement of one song. This input was complemented by the outcome of an interview study, in which percussive guitarists highlighted functional and creative requirements to suit their needs. We ran a pilot study to assess the resulting prototype, involving two other players. We present their feedback on two configurations of the prototype, one equalising the signal of surface sensors and the other based on sample triggering. The equalisation-based setting was better received, however both participants provided useful suggestions to improve the sample-triggering model following their own auditory imagery.

It has been proven, and it is well documented in literature, that the directional response in HRTFs comes largely from the effect of the pinnae. However, few studies have analyzed the contribution given by the remaining part of the external ear, particularly the ear canal. This work investigates the directionally dependent response of the modeled ear canal of a dummy head, assuming that the behavior of the external ear is sufficiently linear to be approximated by an LTI system. In order to extract the ear canal’s transfer function, two critical microphone placements (at the eardrum and at the beginning of the cavum conchae) have been used. The system has been evaluated in several positions, along the azimuth plane and at different degrees of elevation. The results point out a non-negligible directional dependence that is well within the normal hearing range; based on these findings, physical models of the ear canal have been analyzed and evaluated. We have also considered the practical application to binaural listening, and the coloration originated by the superimposition of the contribution of two ear canals (the listener’s and the dummy head’s). A compensating FIR filter with arbitrary frequency response is discussed as a possible fix.