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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 b

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't reduce the outside volume as much as covered headphones do. So then they get the outside noise, plus the increased volume from the earbuds. OT tip - I bought a pair of cheap $30 noise protection ear muffs that I am rarely without when travelling on damagingly loud public transit, such as when I'm commuting on underground rail. They are conspicuously large and odd looking, but my earbuds fit nicely under them, and the travel and listening experience is greatly enhanced, and pleasantly much quieter.

bornfreddy 4y ago
> 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 principle?
- WalterSear 4y ago
  No question that the physics is the same. 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.
  - bornfreddy 4y ago
    Ok, so the design improvements made sounds more synced, but imho that doesn't solve the problem (it might even make it worse? Not sure...). The combing effect is there because the sources of the sound and the "anti-sound" are not in the same position. Lower latency helps that the signals are perfectly cancelled in some predefined direction, but you still get twice the sound amplitudes at a different angle (towards the head).

bornfreddy 4y ago

> 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 principle?

WalterSear 4y ago
No question that the physics is the same. 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.
- bornfreddy 4y ago
  Ok, so the design improvements made sounds more synced, but imho that doesn't solve the problem (it might even make it worse? Not sure...). The combing effect is there because the sources of the sound and the "anti-sound" are not in the same position. Lower latency helps that the signals are perfectly cancelled in some predefined direction, but you still get twice the sound amplitudes at a different angle (towards the head).