I was reading some of papers about the Active Noise Cancellation; in particular about the Filtered-x LMS algorithm, also known as FxLMS.
It seems that classic FxLMS (also called Feedforward FxLMS) algorithm is suitable to cancel broadband noise (white noise), while its Feedback version (the Feedback FxLMS, also abbreviated to FB-FxLMS) is suitable to cancel a narrowband noise (like sinusoid + white noise), but not a broadband noise.
I read that this is due to the fact that the Feedforward FxLMS has the primary noise provided as reference signal, while the FB-FxLMS has not the reference signal initially available, but it needs to estimate it (using the error signal). And this estimation process is possible only if the primary noise has a predictable nature, so it can't be a white noise.
Is there someone (maybe who has already worked with the Feedback FxLMS algorithm) who can confirm this property of the Feedback FxLMS?
PS: As requested in the comments, here are the block diagrams of the two algorithms:
- FxLMS block diagram:
- Feedback FxLMS block diagram