Amplified guitars with pickups tend to sound ’dry’ and electric, whether the instrument is acoustic or electric. Vibration or pressure sensing pickups for acoustic guitars do not capture the body vibrations with fidelity and in the electric guitar with magnetic pickups there often is no resonating body at all. Especially with an acoustic guitar there is a need to reinforce the sound by retaining the natural acoustic timbre. In this study we have explored the use of DSP equalization to make the signal from the pickup sound more acoustic. Both acoustic and electric guitar pickups are studied. Different digital filters to simulate acoustic sound are compared, and related estimation techniques for filter parameters are discussed.

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In this study we have developed a digital guitar body mode modulation technique where the modulation can be controlled through one driving parameter. The filtering and modulation is done with frequency-warped recursive filters that have been implemented in real-time on a modern DSP processor. By changing the warping parameter the perceived size of the body can be controlled, by a pedal or automatically, resulting in an interesting effect. This effect is useful both for the electric and the amplified acoustic guitar. Perceptual properties of the effect are studied by a listening experiment. (See also www.acoustics.hut.fi/demo/dafx2000-bodymod/)

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In this study we present morphing methods for musical instrument body models using DSP techniques. These methods are able to transform a given body model gradually into another one in a controlled way, and they guarantee stability of the body models at each intermediate step. This enables to morph from a certain sized body model to a larger or smaller one. It is also possible to extrapolate beyond original models, thus creating new interesting (out of this world) instrument bodies. The opportunity to create a time-varying body, i.e., a model that changes in size over time, results in an interesting audio effect. This paper exhibits morphing mainly via guitar body examples, but naturally morphing can also be extended to other instruments with reverberant resonators as their bodies. Morphing from a guitar body model to a violin body model is viewed as an example. Implementation and perceptual issues of the signal processing methods are discussed. For related sound demonstrations, see www.acoustics.hut.fi/demo/ dafx2001-bodymorph/.

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