Challenges of musical instrument reproduction including directivity

Reproduction of music from a solo instrument or singers by a single loudspeakers can suffer from lack of presence and liveliness if the directivity is missing. In particular, natural solo music contains the effects of a time-varying directivity with particularities in the directivity index, shape, yielding different coloration of diffuse reverb, early reflection, and direct sound. Focusing on the root of technical realization, it would be desirable to capture and reproduce a recording of an instrument played within a spherically surrounding microphone array in an anechoic chamber. This contribution reviews fundamentals (the soap bubble model) and technical solutions for this particular recording and playback problem, utilizing surrounding spherical microphone arrays and compact spherical loudspeaker arrays, also an application in which a trombone with directivity had been transmitted live from Graz to Paris. However, these solutions need to be carefully used as they hide some essential challenges: Surrounding spherical arrays suffer from the acoustical centering problem and the comb-filtering artifact it creates, and compact spherical loudspeaker arrays for directivity synthesis are subject to a trade off between bandwidth and spatial resolution against temporal resolution. For some of these challenges, alternative approaches will be addressed.