Electronic musical instrument2009-10-12 00:00:00/>
Each partial from the sequential list is digitally generated by stepping through a ROM containing a single cycle forming the frequency of that partial and combining it with the amplitude envelope for that partial resulting in a signal with thedesired frequency, amplitude, duration and attack and decay rates. All the partials are summed into a digital data stream which is converted to an analog form,
filtered and made available for use, for example by an audio amplifier and speakers producingsound.
With reference to the preferred embodiment a sine wave is digitally stored and sensed at an appropriate rate of change of phase angle per sample frequency of a given partial. The phase angle determines the next value selected from the storedsine wave so that changing the rate of change of the phase angle changes the resulting frequency. The stored amplitude is scanned synchronously with the sine wave scanning in a pipe line design ensuring the proper time relationship between the two. Since a partial is a waveform multiplied by an amplitude, both are stored in log form, then added and the anti-log generated forming the resultant partial as a digital stream of signals.
The technique has many useful properties. One is that the quality of a given sound increases as more partials are used to represent it. Another is that partials are controlled independently of one another. This feature allows less importantpartials to be "stolen" from notes already sounding, and used to form new notes. Taken together, these two properties allow both the ability to play many complex timbres simultaneously, as well as allowing enhanced quality for notes played singly or insome instances against a demanding background of silence. This is in contrast to many commercially available synthesizers, which allow only a limited number of voices. The latter force entire previously played notes to be silenced as more notes areplayed (e.g., a 10-note chord played on an 8-voice synthesizer).
Additionally, multiple partial synthesis can be used with sound modelling data stored in one or more read only memories to lower the cost of extra installed voices, because of the greatly reduced storage requirements that go withpartials-synthesis. One second of waveform table as in conventional wave table storage may be tens of Kilobytes, whereas the information that describes a sound and the 10 to 50 partials needed to synthesize the same sound with the present inventionwould be smaller by a factor of up to 20. Similarly, having several voices available at once for a keyboard split or orchestral effect is much less expensive.
The sound model data comprises, in accordance with the invention, the amplitude envelope for each partial as a series of exponential "segments" stored in ROM. Segments have the properties of duration (time) and rate/direction of change(attack/decay). During each segment, the amplitude of a given partial increases or decreases exponentially at a fixed rate maintained by the hardware of what is described herein as a sound engine. Thus, all the processor of such engine has to do isupdate the rate of change of amplitude for each partial after the apropriate duration, starting the next segment.
The invention allows maintenance of a far greater number of accurate models for sounds available at all times compared to prior art capability. A digital model of the sound generation process is calculated in real time, as opposed to playing outa sample table. Each note on each pitch of each voice can be modeled separately, to any required accuracy, if so desired.
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