What’s the Difference Between Passive and Active Noise Cancellation? (.PDF Download)

The term “noise cancellation” embodies a number of different approaches to eliminating unwanted outside noise in order to enhance the listening experience. With so many terms, such as active noise cancellation, ambient noise cancellation, and adaptive noise cancellation, it can get confusing for an end user or system developer to determine the ideal noise-cancellation technology.

As the use of smartphones, digital assistants, and other devices for music playback move further into the mainstream, audio features like noise cancellation become more important to help ensure higher-quality audio playback and phone calls. With OEMs looking for new ways to differentiate their products and appeal to the discerning consumer, digital headsets that offer compelling noise-cancellation technology stand ready to capitalize.

The purpose of this article is to review some basics of noise cancellation, such as the differences between passive, active, and total noise cancellation, as well as compare the different noise-cancellation architectures including feed-forward, feedback, and hybrid. It will also contrast fixed filters versus the more progressive adaptive noise-cancellation approaches. 

Passive Noise Cancellation

Passive noise cancellation is what the headset itself offers, whether rubber tips in an in-ear design or padding in an over-the-ear design. Very simply, it’s the amount of noise cancellation offered by the physical device, or how well the headset works as an earplug. While a good design will provide strong passive cancellation before electronics are applied, passive cancellation is often limited to cancelling frequencies above 1 kHz. Even the best active electronics can’t compensate for poor acoustic design with minimal passive cancellation.

Active Noise Cancellation

Active noise cancellation (ANC) is the process of using a microphone to monitor environmental noise and creating anti-noise that’s then mixed in with audio playback to cancel noise entering the user’s ear. Active noise cancellation can be achieved with analog filters or digital filters, and is generally differentiated by architecture: feed-forward cancellation, feedback cancellation or hybrid cancellation. As mentioned, great active cancellation will significantly improve a headset with good passive cancellation, but can’t make up for poor design.