Audio Test for TWS Earphone.pdf

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Shenzhen MegaSig Measurement and Control Technology Co., Ltd www.megasig.com
1st
Consumer Electronics Testing
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Audio Test for TWS Earphone
MegaSig Measurement & Control Technology Co. Ltd.
www.megasig.com

2nd
Update Date Responsible Description
2022.11.10 Jiang Weiyuan First Draft
Table of Contents
1、The development history of TWS headphones...........................................................................................3rd
2、Introduction to the concept of ENC/ANC.................................................................................................. 3rd
2.1、ENC Concept................................................................................................................................... 3rd
2.2、ANC concept.................................................................................................................................... 4th
3、ENC and ANC test solutions.......................................................................................................................5th
3.1、ENC test solution............................................................................................................................. 5th
3.2、ANC test solution........................................................................................................................... 11th

3rd
1. The development history of TWS earphones
TWS earphones are also known as True Wireless Stereo (True Wireless Stereo) true wireless
stereo. They are mainly connected to mobile phones through Bluetooth modules without wires.
The early Bluetooth technology was immature, resulting in poor sound quality, which was only
suitable for business calls. After 2008, the Bluetooth A2DP protocol began popularizing, and the first
batch of consumer-grade Bluetooth headsets was born. (Not True Wireless)
In 2014, the first "True Wireless" Bluetooth headset was launched. Still, the market response was
not great, until after the release of Apple's Air pods in 2016, accompanied by the birth of Bluetooth
5.0 and 5.1 technology, the audio transmission loss was compressed to the minimum, the "True
Wireless" Bluetooth smart headset has ushered in the outbreak.The audio quality control of TWS is
also increasingly valued by the market. And audio test for TWS earphone is more and more
important in the manufacture process.
2.2 Introduction to the concept of ENC/ANC
2.1 ENC Concept
Active noise cancellation and environment noise cancellation are different noise cancellation
technologies. Active noise cancellation is to offset ambient environment noise to the greatest extent,
allowing people using headphones to enjoy a quiet environment, while environment noise
cancellation is an application in the other direction, it allows people using noise-canceling
headphones to make a call on the side of a noisy road, on a speeding motorcycle, in a moving car
with music on, or in a car with windows open. The person on the other side of the phone can hear
your speech clearly, and the noise basically does not pass. Simply it means, active noise
cancellation means that people who use headphones feel better, and environment noise
cancellation means that people on the other end of the phone feel better. In audio test for TWS
earphone, ENC function is also very important to test.

4th
2.2 ANC concept
With the development of TWS technology, another equally popular technology is ANC (Active Noise
Cancellation), which is active noise cancellation, a kind of noise reduction technology applied in the
headphones for noise reduction.
The ANC noise reduction technology analyzes the sound waves of the noise, and then
superimposes and neutralizes them by sending reverse sound waves, so as to achieve the effect of
eliminating noise. The advantage is that the control effect of low-frequency noise is remarkable, and
it can effectively isolate low-frequency noise and reduce the impact of noise on people's health. In
general, the effective frequency of ANC active noise cancellation is between 50Hz and 2kHz. For
noise exceeding 2KHz, noise-cancellation headphones can reduce it by using passive methods
through the structural design and material selection of the headphones. In audio test for TWS
earphone, ANC performance is also very important to test.

5th
3 ENC and ANC test solutions
Different noise cancellation solutions bring users a different noise cancellation experience, MegaSig
can provide customers and partners with a complete test instrument and system solutions from
research and development to mass production.
3.1 ENC test solution
First let's take a look at ENC's test solutions in audio test for TWS earphone
There are 3 main technologies for noise reduction in calls:
1，Beam-forming directional enhancement technology
2，Adaptive filtering technology
3，Uplink bone conduction technology
These three technologies are not new in audio test. Our mobile phones have two microphones (one
is next to the charging port and the other is next to the camera), which have been silently helping us
make calls and noise reduction for many years (so, sometimes we are accustomed to turning off the
earphones and using the mobile phone directly when making a phone call with earphones for fear of
being unclear. This is the main reason).
The essence of uplink bone conduction technology is to transmit the call content by collecting the
vibration signal of face or vocal cord. The noise conduction medium is air, and the vibration of your
face or vocal cords are directly collected by the acceleration sensor, which can isolate the
environmental noise. This technology is widely used in the military, making a phone call in a tank or
in a helicopter.
3.1.1 Environmental Noise Cancellation effect test in the Research and
Development stage

6th
a) Environmental Noise Cancellation of Beam-forming algorithm in research and
development stage
The following figure shows the effect of TWS headphones with Beam-forming in our office.
The system architecture is in the figure below. We use the turntable TT625 to measure the HFP
transmission energy of each angle of the earphone. If we use the frequency sweep signal, it can be
considered that the adaptive filter has not converged yet, i.e., the received signal can be considered
to be enhanced by beam-forming only.

7th
b) Adaptive filtering algorithm in R&D stage
R&D testing not only needs to quantify the beam-forming effect, but also needs to carry out the
convergence effect of the adaptive filter, and even test the convergence time. Both of them are
supported by AudioExpert platform.
c) Bone conduction technology in the R&D stage
In audio test for TWS earphone, bone conduction can be divided into uplink/downlink bone
conduction call technology, the former is to allow the other party to hear clearly, and the latter is to
allow yourself to hear clearly. We will focus on the uplink bone conduction technology.
In the process of talking, the sound of our own speech is the useful signal we really want to
transmit, but in addition, there are various noises generated by machinery and equipment, wind
noise, surrounding people, etc., which can be called Noise signals.

8th
The essence of the uplink bone conduction technology is to collect the vibration signal of the cheek
by inserting an acceleration sensor chip into the earphone and transmit the effective signal as the
content of the call. The conduction (air conduction) of the ambient noise depends on the microphone,
so it will not be collected by the acceleration sensor, which can achieve the effect of air conduction
noise filtering.
When we speak, in addition to the vibration of the face, the vibration of the bridge of the nose is also
relatively strong, so this technology is not only used in the field of headsets, but also in VR or AR
smart wearable devices to improve the effect of calls.
From the test of the uplink bone conduction call technology, it can be divided into three parts: the
incoming IQC chip test, the semi-finished bone voiceprint test and the finished bone voiceprint test.
The following three tests are supported and compatible with our MegaSig system.

9th
3.1.2 Test of call noise reduction effect in mass production
Over the past two years, MegaSig has supported batches of headsets with ENC function and mass
production testing of TWS earphones with ENC function. Now we will introduce the accumulated
experience to you.
There are 3 main testing methods for mass production:
1, Signal-to-noise ratio test
2, Loop test
3, Switch test
There are advantages and disadvantages to these three methods in audio test for TWS earphone,
and the system of MegaSig supports them seamlessly. The analysis and introduction are below.
1) Signal-to-Noise Ratio test
This method does not require the support of the chip manufacturer's instructions, and basically, any
instrument can support it, and the measurement environment is similar to the real-time environment,
and the noise reduction data tested is close to the real effect. However, because the algorithm is
always on, it is easy to be disturbed by the environment, and the test data is not very stable.
Sometimes it needs to be retested to pass, and it takes some time to wait for convergence, so the
test efficiency and yield are relatively low.
2) Loop test
This method requires the support of chip manufacturers or solution providers and have to control the
DUT. Moreover, in the form of TWS, it does not support too many thimble points, so SPP or BLE
protocol is generally used. However, since this test method strips the influence of the algorithm, it is

10th
possible to measure the quality and assembly errors of the dual microphones. The consistency is
very high, there is no convergence time, and the test efficiency is also high. High-end brands also
pay attention to ENC quality, basically will tend to use this method. At present, MegaSig’s system
can support the DUT control of the general Bluetooth chips on the market.
3) Switch test
In this method, the penetration effect of noise energy is tested through the switch of the DUT.
Since this test has only one angle, the noise suppression capability of beam-forming is basically
ignored, the DUT command is also required, and the convergence time is required, so this
method is least recommended for mass production. However, it is recommended to use it in the
research and development stage to test the effect of the adaptive filter, and some manufacturers
choose this method in the early mass production test of single-mic noise reduction.

11th
3.2 ANC test solution
In audio test for TWS earphone, the noise reduction effect of ANC noise-canceling headphones is
determined by two aspects, one is the design of the filter chain of the product, and the other is a
series of noise reduction gain values of the product. In the R&D stage, the filter chain design has
been finalized and will not be changed in the mass production stage. However, due to the difference
in the quality of incoming materials for the microphone unit and the speaker unit, as well as the
cavity difference generated during the assembly process, to make up for these tolerance and
achieve the target noise reduction effect and balance the noise reduction effect, during mass
production, the noise reduction gain value needs to be fine-tuned and modified, and the noise
reduction effect can be tested online. The traditional method is to manually adjust the gain, manually
verify it until it meets the noise reduction effect, and then manually burn it.
AudioExpert's ANC option supports all mainstream noise reduction solutions on the market, as well
as automated testing and burning systems. MegaSig cooperates with first-class ODM
manufacturers and solution providers and has successfully pushed this system to R&D and Mass
production, creating value for customers stably and efficiently.
The system also supports the measurement of key electro-acoustic parameters that are concerned
in the production process of headphones, microphones, and other components when the ANC
function is turned off. It is a one-stop test system.
The software parameter configuration of the system is simple and fast, the testing process is fast
and accurate, the production efficiency is maximized, the product quality is guaranteed, and the
company wins the time and the trust of the customers, and finally obtains a larger order and
achieves a win-win situation.

12th
ANC noise reduction automation test Universal architecture

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