humcanceling

Hum canceling, also written as humcanceling, refers to techniques used to reduce or eliminate hum, a low-frequency electrical interference that appears in audio signals. Hum commonly originates from mains power (typically 50 or 60 Hz) and their harmonics, but can also arise from ground loops, EMI from nearby equipment, or power supplies. In recording, live sound, and instrument electronics, hum can mask desired signals and reduce clarity.

Techniques for hum canceling fall into passive, active analog, and digital approaches. Passive methods emphasize preventing hum from being picked up or transmitted: using balanced cables and connections, proper shielding, robust grounding, isolation transformers, and quality enclosures. Active analog hum cancelation includes circuits such as notch or band-stop filters that target the mains frequency and its harmonics, and adaptive resonators that adjust to the actual hum. Digital and DSP-based methods use adaptive cancellation algorithms, reference hum signals, and real-time notching to subtract the hum component while preserving the desired signal, often in combination with high-pass filtering to remove very low frequencies.

Hum canceling is widely used in microphone preamps, guitar and bass electronics with hum-canceling pickups, audio interfaces, and broadcast equipment. While effective, cancellation can introduce artifacts if the hum varies in frequency or amplitude, or if nonlinearly coupled signals complicate the cancellation. In some cases residual hum remains, motivating ongoing work to improve robustness under non-stationary conditions and in portable devices.