In Mechanical Sound Synthesis, real mechanical devices are employed to create sound. Users can interact directly with the variables of the sound synthesis, making interactions more intuitive to both users and audience. We focus on real-time feedback control for Mechanical Sound Synthesis and provide a classification scheme using the reality-virtuality continuum. We discover an apparently novel paradigm, which is described as augmented virtuality for real-time feedback control. Exploring this paradigm, we present preliminary results from a system enabling a user to teleoperate acoustic percussion instruments with the aid of force feedback. Mechanical looping of the teleoperation trajectories and their transformations enables the synthesis of lifelike sounds with superhuman characteristics that are nevertheless produced by mechanical devices.

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Acoustic feedback is capable of driving an electroacoustic amplification system unstable. Inserting a frequency shifter into the feedback loop can increase the maximum stable gain before instability. In this paper, we explain how frequency shifting can effectively smooth out the feedback loop magnitude response and how this relates to the system stability. Then we describe measurements on real acoustic systems that we employ to study the practical performance. Although useful for stabilizing systems in reverberant environments, reasonably small amounts of frequency shifting do not provide a significant benefit for hearing aids. It can be helpful to employ a microphone with a focused directivity pattern, and we describe how the directivity pattern may affect the efficacy of frequency shifting.

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