Frequency shifting adds a fixed Hz offset to every partial, breaking harmonic ratios into inharmonic spectra

Frequency shifting (as in Surge XT’s Bode-modelled Frequency Shifter effect) moves every frequency component of a signal up or down by the same absolute amount in Hertz, unlike pitch shifting which multiplies all frequencies by a common ratio. Because a harmonic series (100, 200, 300 Hz…) shifted by +50 Hz becomes (150, 250, 350 Hz…), the integer ratios between partials are destroyed and the tone becomes inharmonic, metallic, or bell-like. Small shifts of a few Hz produce slow phasing/beating; larger shifts (up to ~1 kHz here) produce dramatic clangorous timbres. Surge’s version adds independent left/right shift amounts for stereo motion, plus a delay-and-feedback loop that repeatedly re-shifts the echoes, so each repeat drifts further inharmonic — a classic sci-fi/space effect.

Examples

Shift a sustained sawtooth by +7 Hz for slow metallic phasing; raise to +300 Hz with feedback delay so each echo climbs further out of tune.

Assessment

Explain why a +50 Hz frequency shift makes a harmonic tone inharmonic while a +1 semitone pitch shift keeps it harmonic. What does the feedback delay in Surge’s Frequency Shifter do to successive repeats?