Project Overview
Active noise cancellation and call noise reduction are distinct noise reduction technologies. Active noise cancellation aims to minimize environmental noise to the greatest extent, allowing the user of the headphones to enjoy a quiet environment. On the other hand, call noise reduction is applied in a different context; it enables users of noise-cancelling headphones to make phone calls on a noisy street, or while riding a motorcycle, or in a car with music playing or windows down, and ensures that the person on the other end of the call can clearly hear your speech without much background noise interference. In simple terms, active noise cancellation is about the comfort of the headphone user, while call noise reduction is about the clarity of communication for the person on the other end of the call.
There are three main technologies for call noise reduction:
Beamforming - Directional enhancement technology that focuses the microphone's sensitivity in a specific direction to capture the speaker's voice more clearly.
Adaptive Filtering - A technique that adjusts the filtering process in real-time to better distinguish and isolate the speaker's voice from background noise.
Bone Conduction Technology - A method that uses vibrations conducted through the bones of the user's head to pick up their voice, which can help in noisy environments by providing an additional source of voice signal that is less affected by ambient noise.
These three technologies are not actually new; our smartphones, which typically have two microphones (one next to the charging port and the other near the camera), have been quietly assisting us with call noise reduction for many years (hence, sometimes when we are worried about not being clearly heard on a call with headphones, we instinctively switch back to the phone itself—this is mainly the reason). The essence of the bone conduction technology is to collect vibration signals from the face or vocal cords for call transmission. Since environmental noise is transmitted through the air, using an accelerometer to directly capture the vibrations from your face or vocal cords can isolate the environmental noise. This technology is widely used in the military, such as making calls inside tanks or on helicopters.
Now, the form factor of TWS (True Wireless Stereo) earbuds has accelerated the application of these three technologies. The golf club-like shape of TWS earbuds allows for a greater distance between the dual microphones, enhancing the effectiveness of the beamforming algorithm; the semi-in-ear form factor of TWS allows for more efficient transmission of vibrations from the ear cartilage to the accelerometer, resulting in higher signal-to-noise ratio for the bone conduction; at the same time, the optimization of computing power and power consumption of Bluetooth chips enables these algorithms to run better on TWS chips.
Today, we are discussing beamforming directional enhancement technology.
We also hope that this article can help everyone avoid redundant investment in equipment. Call noise reduction will definitely become a standard feature for mid-to-high-end TWS earbuds, and earphone manufacturers need to be sensitive to this trend and make cautious choices in testing equipment investment. It is necessary to choose a system that can be upgraded for call noise reduction testing; otherwise, it may be necessary to spend a significant amount of money to upgrade the existing Bluetooth audio testing system or purchase a new one that supports call noise reduction testing. In fact, with good planning, regular Bluetooth acoustics and call noise reduction can be completed at one station, and our system supports this.
An Introduction
What is Adaptation—The process of adaptation is an ongoing process of getting closer to a target; an important characteristic of adaptive filtering is the capability to operate in unknown environments and to track the time-variant features of the input signals; in other words, by adapting to environmental changes, the parameters and structure of the filter are altered using the adaptive filtering algorithm to achieve ENC call noise reduction.
In terms of R&D testing, the following need to be assessed: the convergence effect and convergence time of the adaptive filter.
The convergence effect test typically involves the dual-microphone recording capability of the headphones when the adaptive filtering algorithm is activated. Noise is played through a speaker, and the collected audio signals are analyzed. A significant reduction in the noise amplitude signifies the convergence effect of the adaptive filtering algorithm; by issuing commands to deactivate the algorithm and collecting noise, this represents the scenario without the convergence effect of the adaptive filter.
-------On-Off Testing Method; This approach measures the noise energy penetration by toggling the DUT's operation. As this test only considers a single angle, the noise suppression capability of beamforming is essentially disregarded. Additionally, it requires DUT instructions and convergence time, making this method the least recommended for mass production scenarios. However, it is suggested for use in the R&D phase to evaluate the adaptive filter's performance, and for mass production testing of early single-microphone noise reduction, some manufacturers opt for this method.
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