Active noise cancellation decisions in a portable audio device

Active noise cancellation (ANC) circuitry is coupled to the input of an earpiece speaker in a portable audio device, to control the ambient acoustic noise outside of the device and that may be heard by a user of the device. A microphone is to pickup sound emitted from the earpiece speaker, as well as the ambient acoustic noise. Control circuitry deactivates the ANC in response to determining that an estimate of how much sound emitted from the earpiece speaker has been corrupted by noise indicates insufficient corruption by noise. In another embodiment, the ANC decision is in response to determining that an estimate of the ambient noise level is greater than a threshold level of an audio artifact that could be induced by the ANC. Other embodiments are also described and claimed.