Polyphonic tone synthesizer with loudness spectral variation

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 computed and in which the data words are transferred sequentially and repetitively from a note register to a digital-to-analog converter at a rate proportional to the pitch of the tone being generated apparatus for generating additive tones each having a variable spectral content comprising;

• a first memory means for storing a master data set comprising said plurality of data points to be thereafter read out,
• a signal generator means for generating a control signal,
• a plurality of transform memory means for storing a plurality of sets of transform data values,
• an addressing means responsive to said control signal for addressing transform data values from said plurality of transform memory means,
• summation means for adding said addressed transform data values thereby generating elements of said master data set,
• a second addressing means for writing output from said summation means into said first memory means during each computation cycle of a sequence of computation cycles,
• a third memory means for storing data to be thereafter read out,
• a transfer data means wherein said master data set values stored in said first memory means are translated in magnitude to produce a zero average value and transferred to be stored in said third memory means,
• a reading means for sequentially and repetitively reading out data stored in said third memory means, and
• means for producing musical signal waveshapes from data read out by said reading means.

A digital polyphonic tone synthesizer in which tones of variable spectral content are generated in response to control signals comprising;

• a keyboard comprising a plurality of key switches,
• a plurality of tone switches wherein each setting of the tone switches corresponds to the selection of a predetermined tone of variable spectral content,
• a plurality of transform memories each containing a set of transform data values.
• a signal generating means for generating control signals,
• a plurality of addressing means responsive to said control signals for addressing transform data values from said plurality of transform memories,
• summation means for adding said addressed transform data values,
• a main register for storing added values from said summation means to be thereafter read out,
• a plurality of registers,
• transfer means whereby data stored in said main register is read out, translated in magnitude to have a zero average value, and transferred to selected members of said plurality of registers,
• a plurality of variable frequency clock generators each associated with a member of said plurality of registers whereby data is addressed out of associated registers at a selected clock rate,
• means responsive to operation of any member of said plurality of key switches for setting the frequencies of said clock generators to predetermined values assigned to key switches,
• digital-to-analog converter means connected to said plurality of registers, and
• means for repetitively and sequentially reading data from each of said plurality of registers and providing the data to said digital-to-analog converter means in synchronism with said associated clock generator, whereby the digital-to-analog converter means generates a plurality of analog output signals each having a fundamental frequency determined by a selected key on said keyboard and a waveshape determined by the combination of the setting of said tone switches and the magnitude of said control signals.