Physical model musical tone synthesis system employing truncated recursive filters
AssigneeStaccato Systems Inc.
InventorsJulius O. Smith, III, Maarten Van Walstijn
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Abstract
A tone synthesis system employs digital filtering methods to enable the practical usage of unstable filter elements in a real-time synthesis model. Truncated infinite impulse response (TIIR) filters are used to approximate portions of the reflection impulse response of an acoustic horn such as a trumpet bell. Methods for resetting filter state enable the use of internal unstable filter poles. Similar state resetting methods enable the use of unstable one-pole filters in the scattering junction formed between two conical acoustic bores. High quality tone synthesis can be achieved without the necessity of a complicated filter representing large sections of the bore of a woodwind instrument.
Claims22
An electronic tone synthesis circuit for synthesizing a tone resembling that produced by a wind instrument having an acoustic tube bore, the circuit comprising:
- a) an input for receiving an excitation signal;
- b) a delay for delaying a digital signal;
- c) an infinite-impulse-response (IIR) filter for digitally filtering the digital signal;
- d) an output for providing a digital output representing a synthesized tone;
- and
- e) a filter truncation circuit for truncating an impulse response of the IIR filter after a predetermined number of samples;
- wherein:
- i) the delay and filter are connected in series with feedback to form a filtered delay loop;
- ii) the input injects the excitation signal into the filtered delay loop;
- iii) the output extracts the digital signal from the filtered delay loop;
- and
- iv) the delay and filter introduce a total time delay of the digital signal, wherein the total time delay is inversely proportional to an approximate pitch of the synthesized tone.
A method for electronically synthesizing a tone resembling that produced by a wind instrument having an acoustic tube bore, the method comprising:
- a) providing an excitation signal;
- b) combining the excitation signal with a digital signal propagating in a filtered delay loop;
- c) delaying the digital signal propagating in the filtered delay loop by a total delay inversely proportional to the approximate pitch of the synthesized tone;
- d) digitally filtering the digital signal propagating in the filtered delay loop using an infinite impulse response (IIR) filter having at least one unstable pole;
- e) outputting the digital signal from the filtered delay loop to produce the synthesized tone;
- and
- f) truncating an impulse response of the IIR filter after a predetermined number of samples, thereby implementing a truncated infinite impulse response (TIIR) filter.
Dependencies are inferred from the claim text.