harmonic equalizer is the working title

Signal input feeds a phase-locked loop (PLL) circuit which detects the input frequency and converts it to a variable DC control voltage. This control voltage is used to control several voltage-controlled bandpass filters, such that the center frequency of each band is on a harmonic of the input frequency. Unlike a typical graphic or parametric equalizer, the boost or cut applied to each band will track the input frequency. For example, if the fundamental frequency is cut but the first harmonic is boosted, the circuit should function similarly to frequency doubler. Timbre is closely related to harmonic content, so such a device should be able to alter the timbre of an instrument equally over its entire range. Additionally, the PLL circuit allows for the addition of synthesized tones above or below the fundamental frequncy by placing frequency dividers in the loop.