1Helsinki University of Technology, Laboratory of Acoustics and Audio Signal
Processing, Espoo, Finland
2Sibelius Academy, Centre for Music and Technology, Helsinki, Finland
A sound synthesis algorithm for the harpsichord has been developed by applying the principles of digital waveguide modeling. A modification of the commuted waveguide synthesis approach is used, where each tone is generated with a parallel combination of a string model and a resonator that are excited with a common excitation signal. The parallel resonator is used, as proposed previously, to reproduce the beating effect appearing in many harpsichord tones. A modification to the loss filter of the string model is introduced which allows more flexible control of decay rates of partials than a typically used first-order filter. The characteristic thump terminating tones played with the harpsichord is reproduced by triggering a sample that has been extracted from a recording. A digital filter model for the soundboard has been designed based on recorded bridge impulse responses of the harpsichord. The output of the string models is injected in the soundboard filter that imitates the reverberant nature of the soundbox and particularly the ringing of the short parts of the strings behind the bridge.
Keywords: acoustic signal processing, computer music, digital filter design, digital signal processing, digital waveguide modeling, electronic music, musical acoustics, physical modeling of musical instruments, sound synthesis
Example of the sound of the instrument recorded this study.
The basic Karplus–Strong algorithm produces sounds that are reminiscent of the harpsichord for many listeners, but only when a high sample rate is used. This synthesis technique has been shown to be a simplified version of the waveguide string model that is extensively used for synthesis of stringed instruments and that we use in this work.
Our synthesizer uses two sample databases, one for the excitation signals and another for release sounds.
The ripple filter inserted in the loop of the string model enables interesting timbral variations. It allows large deviations in the decay rate of different harmonics.
In the synthesis model, the response of the soundboard is imitated with a reverberation algorithm, which is similar to those used for simulating room reverberation. The soundbox can be interpreted to be a very small room.
The ringy characteristics of the soundbox response are partly caused by the short ends of the strings behind the bridge. They are not ideally damped, and they produce a faint bell-like sound, when the instrument is played.
The effect brought about by the soundbox reverberation algorithm is heard clearly in staccato tones. Compare the following two synthetic examples:
Compare also the following two synthetic examples:
Finally, listen to the following short piece of baroque music played on the harpsichord synthesizer: J. J. Froberger, Gigue, A minor, Suite no. 30 (46 sec, MP3, 558 kB).
Created: October 20, 2003
Last modified: March 29, 2006
Author: Vesa Välimäki