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OTC Hearing Aid Audio Testing App Note
1、Overview
According to the WHO report, more than 1.5 billion people worldwide are hearing impaired, which has a major impact on communication interaction, social participation, and overall health and quality of life. Despite the high prevalence and public health impact of hearing loss, only about one in 10 people who would benefit from hearing aids seek intervention. Most hearing-impaired people live in low- and middle-income regions or countries, and cannot afford the high cost of hearing aids. On October 19, 2021, the US FDA issued a proposal to establish a new category of OTC (over-the-counter) hearing aids, which will take effect on October 17, 2022. The purpose is to make it easier for most hearing-impaired people to obtain hearing aid products. Improve your communication and life.
According to the classification of wearing style, it can be divided into box type, behind-the-ear, in-ear, glasses type and hairpin OTC hearing aids. Then, for the above different types of OTC hearing aids, we have a complete system from software test algorithms to hardware test equipment, which can quickly and accurately present the test data in a visualized manner.
2、OTC hearing aid application testing
2.1、OTC hearing aid test configuration
AB 09 shielding box features:
Audio RF Dual Isolation
Rich access and output terminals
Support manual, program-controlled design
CM 313 Hearing aid strong coupling + A 803 preamp features:
Complies with IEC 60318-5 requirements for 2cm³ acoustic coupler
Cost-effective acoustic coupler compatible with 1" and 1/2" microphones
PM 6143 DAQ features:
4 inputs, 4 outputs
Power amplifier, signal conditioner, acquisition three-in-one
MegaSign private drive, more stable test
AudioExpert audio analysis software features:
Complete Audio Analysis Algorithm Library
Supports automatic sequence editing
Support LabVIEW call
Support for remote control
M 663+A 802 free-field microphone characteristics:
Prepolarized free-field measurement microphone for measuring the undistorted real sound pressure before the microphone is placed in the sound field
SB 05 far-field measurement speaker:
Low frequency boost
For audio tests with high low frequency requirements
AM 581 artificial mouth features:
Accurately simulate the sound source of the sound field near the human mouth, suitable for frequency response, distortion and other acoustic parameter testing of telephone microphones and microphones (microphones)
Higher low frequency transducer efficiency (especially 100-200Hz)
Extremely high sensitivity across the entire frequency band
U 982 Bluetooth adapter features:
Support Bluetooth protocol of SCB \ AAC \ LHDC. (MegaSig also provides other models of Bluetooth adapters that support Bluetooth protocols such as aptX \ LC3 \ BLE)
Supports audio services such as A2DP, HFP (Narrowband, Wideband)
2.2、OTC hearing aid test items
a) Calibration of the test box
Significance of sound field calibration: During calibration, first test the response of the anechoic box, and then correct it by computer to obtain a "flat" sound field. The test data before and after calibration are shown in Table 1. By comparing the test data before and after calibration, it can be seen that the performance parameters of OTC hearing aids are very different, so it is very important to calibrate the anechoic box before the test.
b) Saturation Sound Pressure Level OSPL90
OSPL90:
Frequency Response-OSPL90: Output SPL at 90dB Input SPL
Max @ xxxHz: The maximum value in the frequency response curve of OSPL90
HFA Avg: high-frequency average high-frequency average, the average gain or sound pressure level at 1000Hz, 1600Hz and 2500Hz expressed in decibels (dB)
c) Full-range sound gain FOG50
FOG50:
Frequency Response - FOG50: Output SPL for 50dB input SPL input sound pressure level is 50dB output sound pressure level
Gain Frequency Response - FOG50: FOG50 Curve - 50dBSPL Curve (FOG: FULL on gain)
Max @ xxxHz: the maximum value in the frequency response curve of OSPL50 Gain
HFA Avg: High-frequency average value, the average gain value of the high-frequency average full-on gain at 1000Hz, 1600Hz, and 2500Hz at 3 frequency points
d) Self-noise value
Self-generated noise level limitations. The self-generated noise shall not exceed the sound pressure level of 32dBA decibels. Any method of artificially lowering the apparent noise floor of the measurement must be disabled. These methods include, but are not limited to, auto-mute and scale down.
e) Delay value
Latency must not exceed 15ms. You must use an accurate and repeatable method to measure errors up to 1.5 milliseconds
f) Frequency response breadth
The lower limit cut-off frequency should be extended to 250 Hz or below, and the upper limit cut-off frequency should be extended to 5K Hz or higher. You must perform measurements in accordance with the frequency response bandwidth specified in the method of clause 4.1 of ANSI/CTA-2051:2017
g) THD + N
Total Harmonic Distortion plus Noise shall not exceed 5% for an output level that is one of the following set of levels, according to the test method:
Measured at 70 dB SPL and 100 dB SPL using sine wave based testing; or
Measured at 67 dB SPL and 97 dB SPL using a 500 Hz one-third octave impulse noise signal.
Total harmonic distortion must be measured with an analyzer with a 500 Hz input tone and a bandwidth at least as wide as the frequency limit of an OTC hearing aid.
The output distortion at the maximum volume of the OTC hearing aid must be measured and the input level of the OTC hearing aid adjusted to produce the desired output.
h) Smoothness of frequency response
No single peak in the one-third octave frequency response shall exceed 12 dB above and two-thirds octave below the peak, relative to the average for the one-third octave band. You must measure frequency response smoothness using the value of the diffuse field and the corrected third-octave interpolated response specified in method 4.1 of ANSI/CTA-2051:2017
2.3、OTC hearing aid test stand links
Take the behind-the-ear OTC hearing aid with Bluetooth chip as an example:
1. OTC hearing aid performance test:
After adjusting the gear and volume of the OTC hearing aid, place it on the custom fixture, and then AudioExpert audio analysis software controls the PM 6143 signal acquisition card to make the SB 02 far-field measurement speaker sound. After the microphone of the OTC hearing aid collects the sound signal, Internal processing of the earphone, the sound from the OTC hearing aid speaker is collected by the CM 313+A 803 hearing aid coupler kit, and then the collected signal is sent back to AudioExpert for analysis through the PM 6143.
2. OTC hearing aid routine acoustic test:
① OTC hearing aid speaker test: AudioExpert audio analysis software controls the U 982 Bluetooth adapter to control the OTC hearing aid speaker to emit sound, which is collected by the CM 313+A 803 hearing aid coupling cavity kit, and then the collected signal is returned to AudioExpert for analysis through PM 6143.
② OTC hearing aid microphone test: same link as OTC hearing aid performance testing.