Design Options for Audio Frequency Shifting System for Unique and Interesting Sound Effects

A Frequency Shifter shifts the full spectrum of an audio input signal up and down the frequency axis. When shifted, the harmonic relationships of the input signal are not preserved and the resulting inharmonic signal has an interesting uncommon metallic sound. The frequency shifters, originally developed to supress audio feedback howling, were used in early music synthesizers to create unique special sound effects. Early frequency shifters were implemented with analogue diode ring modulators that suffered from annoying audio carrier tone bleed-through due to mixer imbalance. Implementing the frequency shifter in DSP holds the promise of reduced cost, improved dynamic range, and absence of undesired artifacts.