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Introduction
Recently, the number of ANC compatible models has increased not only for overhead headphones, but also for left and right independent headsets. The ANC function drowns out ambient noise, so it is useful in various situations such as sleeping on an airplane or studying at a cafe. I will touch on the outline of such an ANC function.
What is ANC
Abbreviation for Active Noise Canceling.
What is generally recognized as a noise canceling function is active noise canceling, which actively cancels (attenuates) unwanted background / ambient noise (background noise / ambient noise) that reaches the user's ear. ) function.
It captures background noise through a microphone and generates anti-noise (opposite phase of background noise). Anti-noise is played through the headset speakers. This allows anti-noise and background noise to cancel each other out before reaching the user's ears.
As a result, unwanted noise is drowned out and is not heard by the user.
Characteristics of ANC
Due to the nature of sound waves, ANC is most effective in the low-frequency portion of the acoustic spectrum (the sound pressure, intensity, etc., as a function of frequency). Depending on fit (mechanical) and acoustic properties, they can also cancel out high frequency noise.
At the beginning, we said that active noise canceling is common, but there are also passive noise canceling that blocks noise from reaching your ears, and noise that prevents noise from reaching your ears by improving sound insulation. There is also a passive system called passive noise isolation that blocks noise.
Passive noise isolation and ANC technology are mutually complementary technologies to provide the user with a comfortable listening environment. Depends.
The performance of an ANC system depends not only on the ANC technology, but also on the hardware design.
Method and characteristics
There are the following methods, each with different configurations and characteristics.
・Feed Forward ANC (FF ANC)
・Feed Backward ANC (FB ANC)
・Hybrid ANC
Feed Forward ANC (FF ANC)
In feedforward mode, ANC captures the reference noise before the noise reaches the driver, such as a speaker or receiver. Then it calculates the anti-noise phase of the noise and plays the anti-noise through the speaker.
Feed Backward ANC (FB ANC)
In Feedback (FB) mode, ANC has a microphone that captures the noise that remains in the ear canal* and between the speakers (within the quiet range), and processes this noise with a feedback algorithm to generate the appropriate anti-noise. increase.
FB ANC requires more complex processing than FF ANC because noise mics also pick up music and audio signals sent down the speaker path. In this case the FB filter path is adjusted to remove any residual music or speech signals from the microphone before processing (similar to an echo canceller). Due to the feedback nature of this configuration, erratic performance can occur without careful tuning and proper acoustic design.
Feedback ANC is generally effective at reducing low frequency noise (below 500Hz) and has less directional performance variation than feedforward ANC.
*Ear canal:
A tube-like organ that is closed on one end and extends from the ear canal to the eardrum, where it transmits sound waves to the middle ear.
The ear canal acts like a trumpet tube to amplify sound, and sound waves cause the eardrum to vibrate. This vibration of the eardrum is transmitted to the middle ear.
Hybrid ANC
Hybrid ANC uses FF Path and FB Path simultaneously to maintain the respective advantages of FF and FB.
Hybrid ANC uses a noise (FF mic) and an error mic (FB mic) per channel to capture the reference noise before the actuator (speaker or receiver) and the remaining noise between the ear canal and the speaker (within the quiet range) will be needed.
Signals from noise mics are processed in the FF path, and signals from error mics are processed in the FB path.
Summary
As introduced so far, there are multiple ANC functions, each with different methods, configurations, and characteristics. In addition, there are multiple important items and processes such as hardware design, layout, and tuning work to realize it, and development requires a lot of time, so it is necessary to be careful when planning implementation.
Finally, the ANC function introduced in this article can be realized with Qualcomm® Bluetooth products QC514x Series, QCC304x Series, or QCC3056.
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