Active noise cancellation works by adding phase-reversed copies of background noise

Evidence

Telecommunication devices, such as mobile phones, often involve algorithms to suppress background noise using non-linear DSP methods with time-variant processing. An unwanted side effect is that the noise suppression algorithms may also degrade the quality of speech, especially if the background noise is non-stationary. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 2452 (#qualifies, via linked claim)

Categorization

• XREF: connects to: Superposed sounds cancel or amplify locally without changing each other; Noise-cancelling headphones now deliver up to 30 dB of isolation — Toole, Floyd E, Sound reproduction- the acoustics and…, 1685; Hybrid feed-forward and feedback ANC lowers background noise by up to 30 dB (+5 more)

Related

• Noise suppression algorithms can degrade speech quality in non-stationary noise (similarity 0.89)
• Noise-cancelling headphones now deliver up to 30 dB of isolation (similarity 0.84)
• Passive noise cancellation avoids contaminating the wanted signal that active cancellation risks (similarity 0.83)
• Active noise cancellation applies superposition but tops out near 20 dB reduction (similarity 0.83)
• Antiphase waveforms cancel when added together (similarity 0.82)
• Emission cancellation needs 30-50 dB less level than hearing cancellation (similarity 0.82)
• Active noise cancellation dominates below 1 kHz while passive isolation takes over above it (similarity 0.82)
• Active noise cancellation fails at high frequencies due to phase shift limits (similarity 0.81)
• Speech models built on optimal listening neglect constant signal degradation (similarity 0.79)
• Reducing background noise improves both safety and perceived sound quality (similarity 0.79)
• Active noise cancellation reduces preferred listening volume, protecting hearing (similarity 0.78)

Broader Connections

• An all-pass filter alters phase and timing but not amplitude #expands (0.78)
• Noise suppression algorithms can degrade speech quality in non-stationary noise #qualifies (0.72) — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 2452