1. Field of the Invention
This invention relates to musical tone synthesis and in particular is concerned with an improvement for systematically selecting tone colors.
2. Description of the Prior Art
The current trend toward the use of digital tone generation system is primarily motivated by the quest for a commercially viable musical instrument which can produce good tone characteristics and which can be implemented at a commercially acceptable cost. A flexible type of a musical tone generation system is one in which a musical waveshape is computed from a preselected set of harmonic coefficients by means of a Fourier-type of transform algorithm. Several methods can serve to obtain the set of harmonic coefficients. One technique is to perform a harmonic analysis on tones recorded from acoustic orchestral type musical instruments. A second technique is of the trial and error approach in which the individual harmonics are adjusted in magnitude until a sound is found which satisfies the listener.
The practical problem involved with the simple trial and error technique to determine usable sets of harmonic coefficients lies in the vast number of theoretical combinations possible for even a modest number of harmonic coefficients. For example, a typical digital tone generator many produce tones corresponding to a set of 32 harmonics. Each of these harmonics may have coefficient values that range from 0 DB to about -32 DB. The number of theoretical combinations of 32 harmonics varied in 1 DB step is 1.4614.times.10.sup.48. If one combination is changed each second, it would take 4.7.times.10.sup.40 years to try all possible combinations. Obviously this is far too much time to spend on such a tone seeking enterprise. It should be noted that not all the possible combinations provide tones that a listener would judge to be tonal distinguishable. Moreover many of the possible combinations yield essentially identical tones which differ primarily in their relative loudness.
Digital tone generators that create musical tones by computing a Fourier transform using preselected sets of harmonic coefficients are described in U.S. Pat. No. 3,809,786 entitled "Computer Organ" and in U.S. Pat. No. 4,085,644 entitled "Polyphonic Tone Synthesizer."