Adaptive computation in a digital tone synthesizer
AssigneeKawai Musical Instrument Mfg. Co., Ltd.
InventorRalph Deutsch
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Abstract
In a musical instrument having one or more tone generators in which a plurality of data words corresponding to the amplitudes of a corresponding number of evenly spaced reference points defining the waveform of one cycle of an audio signal are transferred sequentially from a note register to a digital-to-analog converter in repetitive cycles at a rate proportional to the pitch of the tone being generated, apparatus is provided for adaptively computing the set of data points in response to values of preselected harmonic coefficients. The computation apparatus advances past all harmonic coefficients of smaller magnitude than a selected threshold thereby reducing the computation time and making the instrument capable of responding to time varying tonal changes.
Claims12
In a musical instrument having one or more tone generators in which a plurality of data words corresponding to the amplitudes of a corresponding number of evenly spaced points defining the waveform of one cycle of an audio signal are computed by a Fourier transform using stored values of harmonic coefficients and in which the waveform points are transferred sequentially from a note register to a digital-to-analog converter at a rate proportional to the pitch of the tone being generated the improvement for generating said data words in a time interval whose length is determined by the values of the harmonic coefficients comprising:
- a harmonic coefficient memory means for storing values of harmonic coefficients,
- memory addressing means for reading out harmonic coefficients from said harmonic coefficient memory,
- a computation means using said values of harmonic coefficients wherein said data words are computed during a computation cycle,
- a comparator means whereby a comparison signal is generated in response to a preselected value of a harmonic coefficient read out of said harmonic coefficient memory, and
- termination means responsive to said comparison signal whereby said harmonic coefficients are inhibited and not provided to said computation means and whereby said computation cycle is terminated thereby causing the duration of said computation cycle to be altered in response to said preselected value of a harmonic coefficient.
A digital polyphonic tone synthesizer in which musical waveshapes are computed by means of a Fourier transform, wherein the computation is adaptive to the values of the harmonic coefficients used in said transform, comprising;
- a keyboard comprising a plurality of key switches,
- a plurality of tone switches wherein each setting of the tone switches corresponds to a selection of a predetermined sound waveshape,
- a plurality of memories containing values of harmonic coefficients,
- selection means responsive to setting of said tone switches for sequentially selecting harmonic coefficients from said plurality of memories,
- a reference signal generation means,
- a comparison means whereby a comparison signal is created when one of said sequentially selected harmonic coefficients is less than said reference signal, and
- digital computing means responsive to said harmonic coefficients and said comparison signal for generating a master data set comprising points on said musical waveshape according to said Fourier transform.
Dependencies are inferred from the claim text.