Noise meter microphone active noise reduction
Now, your clear voice has been transmitted to your friend through the radio, but this does not mean that the other party can receive your message clearly. At this point, active noise reduction is necessary.
As before, both steady-state and non-stationary noise can affect the sound transmitted to the earplugs. Unlike the previous situation where noise was eliminated, the goal of active noise reduction is to completely cancel out external noise. The microphone captures incoming sound, generates a reverse signal of external noise, and suppresses external noise as much as possible by overlaying the reverse signal onto the incoming sound waves. In summary, this is conceptually similar to adding the numbers+5 and -5 to obtain 0.
In hardware, based on the basic principle mentioned above, active noise reduction can be applied in two main ways. One type is feedforward ANC, which uses a microphone outside of an audible device; Another type is feedback ANC, which uses a microphone in an audible device closer to the ear.
The feedforward ANC is located outside the ear, making it more sensitive to noise. It can clearly capture noise when it is transmitted to audible devices. Then, it can process the noise and output its phase cancellation signal. This enables it to isolate specific sounds, especially mid frequency sounds. This includes the steady-state sound we mentioned earlier in this post, but also includes speech. However, the feedforward ANC is located outside the device, making it more susceptible to external noise, such as wind or the constant friction of earplugs on the inside of the hood (this is definitely not empirical).
The feedback type ANC is not affected by the disorderly hood, as it is inside the audible device and can resist various other accidental interferences. This type of sound insulation effect is good, but the high-frequency sound successfully transmitted into the earplugs is difficult to cancel out. Similarly, the internal feedback microphone needs to distinguish between playing music and noise. Moreover, because its feedback is closer to the ear, it needs to process this information faster to maintain the same delay as the feedforward setting.
Finally, there is hybrid active noise reduction - you guessed it right, which combines feedforward and feedback ANC to achieve the best results in both aspects at the cost of power consumption and hardware.
