Earlier quoted context omitted.
Early forms of active noise reduction did create the comb filtering effects that you describe, but these were never inaudible. Modern noise reduction is much better about this, however, and higher level products are actually used for hearing protection - this is used in headphones for fighter pilots. The problem isn't the noise cancelling as much as people turning up the volume in loud environments, since earbuds don…
> Early forms of active noise reduction did create the comb filtering effects that you describe, but these were never inaudible. Modern noise reduction is much better about this, however, and higher level products are actually used for hearing protection - ... But surely the physics is the same, is it not? The only thing they can improve is timing and where the doubled waves go. Unless they work by using some other p…
I don't have experience in active noise cancelling design, but I would guess that lower latency hardware probably plays a large part in the improvement, given the nature of the problem - a chip set that couldn't 'keep up' with changes in the audio signal would be late in responding, resulting in comb filtering. No doubt, people also improved the algorithms over time too.