Method and apparatus for selective reduction of upper harmonic c

Details Method and apparatus for selective reduction of upper harmonic c Method and apparatus for selective reduction of upper harmonic c

1990-11-01

1993-03-16

Shoop, Jr., William M.

Music

Instruments

Electrical musical tone generation

84672, 84692, 84696, 84698, 307261, G10H 700, H03K 408

Patent

active

051946840

ABSTRACT:
Variable frequency sawtooth waveforms are often utilized as an excitation signal in a digital musical synthesizer. A problem exists at lower sampling rates in such systems due to an aliasing problem which occurs at frequencies near the Nyquist rate. Low pass filtering may be utilized to mask this problem; however, low pass filtering is very time consuming to implement in a ditigal signal processor. The method and apparatus of the present invention reduces the upper harmonic content of a sawtooth waveform by proportionally converting the sawtooth waveform to a triangle waveform in response to variations in the frequency of the sawtooth waveform. This is accomplished by adding a selectable offset to the sawtooth waveform and then taking the absolute value of the resultant waveform. By restoring this waveform to a zero offset, the sawtooth waveform excitation signal will be converted to a triangle waveform having a substantially reduced upper harmonic content. By varying the selectable offset in response to variations in the frequency of the sawtooth waveform, it is possible to efficiently vary the amount of conversion which occurs.

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patent: 4974486 (1990-12-01), Wallace

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