Hearables Testing
Hearable testing – measuring airpods with SoundCheck and a head and torso simulator
Hearables testing represents the convergence of tests from headphones, microphones, telephones, telephony, hearing aids, and more. Between these, a huge number of test stimuli, algorithms, analysis options and signal paths options are necessary, not to mention many ‘useful-to-have’ features such as integrated background noise and a test configurator that makes it easy to run many iterations of a test continuously.
Hearables may include one or more (often all) of the following:
- Headset functionality (includes microphone)
- Active noise cancellation
- Hearing assistance
- Wireless connectivity (Bluetooth)
- Use as a communications device
- Health monitoring
Making measurements on such devices is considerably more challenging than measuring headphones due to the range of tests needed, and connectivity requirements.
Range of tests
In addition to basic acoustic parameters such as headphone frequency response, distortion etc, are many more aspects that need to be measured. This might include microphone performance and ANC performance. It may even be necessary to qualify the devices to hearing aid or communication standards, or to measure voice recognition, maybe in the presence of background noise.
Connectivity and test system needs
Due to their wireless nature, hearables usually need to be tested in an open-loop configuration. This places some specific demands on the test system, and and additional interfaces (e.g. Bluetooth) are often required. Furthermore, the large amounts of on-board signal processing (e.g. voice activity detectors, mic array beamforming, automatic ear detection, loudness control, equalization, active noise control, compressors, etc. means that special consideration needs to be given to the test signals and analysis algorithms used – for some tests, sine sweeps (the most common test signal for traditional applications) are not appropriate.
SoundCheck for Hearables Testing
SoundCheck offers extensive capabilities for measuring hearables. Flexibility is inherent in both the software and hardware design, and Listen has an established track record of testing a wide range of communications devices, hearing aids and more in addition to conventional headphone and headset measurements.
Testing hearables brings together many of the test methods and algorithms we originally developed for other applications, often decades ago. For example, we were the first to introduce open loop testing (originally for MP3 players) back in 2007, although some of its algorithms were first introduced as early as the 1990s. We’ve been testing communications devices and hearing aids since the late 1990s, and we’ve offered the option to use speech or music test signals since 2006. Although well established, these methods have been continually updated and refined over the years to ensure that we have the most advanced algorithms and analysis methods to meet the changing needs of the industry.
Since a SoundCheck system is modular, hardware such as Bluetooth interfaces can easily be added if needed, and similarly, most of the specialist modules used for communications and hearing aid measurements can also be added to a system at any time as testing requirements evolve. Pre-written test sequences are available for a variety of open loop measurements, as well as communications and hearing device test standards.
SoundCheck offers the following benefits for testing hearables:
- Tests both earphones and microphones
- Can create a compound stimulus with frequency and/or log chirp trigger to enable accurate open-loop testing
- Can be set to analyze only parts of the response signal, so that the trigger tone can be eliminated from the analysis
- Can use speech and music as test signals, calibrate levels, and equalize a mouth simulator (includes active speech algorithms)
- Offers background noise generation – although this can be generated externally, testing is much simpler and faster when its created by the test system and integrated with the test sequence
- Accepts a signal via virtual audio cable in order to route in signals from the cloud
- Pre-written TIA and ANSI test sequences are available if device needs to be tested to telephony or hearing aid standards (these may be manually programmed with sufficient expertise)
- The sophisticated sequence writer allows duplication of sub-sequences and loops – essential when repeating a test at various levels
- Calibrated Bluetooth interface available
Measuring Hearables
Following are examples of some of the hearables measurements that can be made with SoundCheck, along with schematic diagrams showing the equipment typically required. Please note that configurations will differ based on specific test requirements, but our engineers are happy to recommend a configuration based on your needs.
Test configuration for basic wired and wireless (Bluetooth) headset measurement
Basic Audio Measurements
Basic acoustic tests such as frequency response, distortion left right, tracking, comparison to reference curves (e.g. Harman target curve) are simple. These tests essentially measure the device under static conditions to measure microphone or microphone array and earphone characteristics such as frequency response, distortion and left/right tracking for stereo headphones. If possible, it is a good idea to measure both wired and wireless performance for comparison. This requires a calibrated headphone amplifier for wired headphone responses and a calibrated Bluetooth interface for wireless headphone responses. In addition, a calibrated mouth simulator, equalized for a constant sound pressure output level versus frequency, and ear simulators are required for both send and receive acoustical response.
See our Headphone testing main page for more information on these measurements.
Test configuration for measuring ANC headphones
Active Noise Cancellation
Both passive and active noise cancellation measurements are simple in SoundCheck, with pre-written measurement sequences to accelerate test development.
The test procedure can be broken down into three measurements and three calculations. First, the
headphones are removed from the head and torso simulator, the noise signal is played, and the spectrum
measured through the open ear. This un-occluded ear spectrum is used as the baseline for the noise.
Next, passive isolation is measured by placing the headphones onto the head and torso, playing the
noise signal again and measuring the noise through the artificial ear. Finally, the measurement is
repeated with the active noise cancellation (ANC) circuit turned on. These measurements result in three spectra which are used to calculate the three attenuation parameters, passive isolation (the noise attenuated simply by the headphones being worn), active Attenuation (the reduction in noise when the
active cancellation circuit is engaged) and the total attenuation of the headphones.
Test configuration for testing via speech activation
Voice Activation and Speech Recognition
Sometimes it is necessary to test devices via speech control with wake words. This is complicated because the test signal usually needs to be in the cloud to enable playback, and each manufacturer’s ecosystem does this differently. Some enable you to upload
your own recordings (although you should bear in mind that these will probably be compressed).
Others require them to be on a media streaming platform such as Spotify. For microphone testing, some systems allow you to access your recordings via their website, whereas others do not for security and privacy reasons. Furthermore, each device needs activating with a different wake word, needs different delay compensation and records for a different amount of time after it hears the wake word. These factors need figuring out (largely by trial and error) for each device that you need to test. Although the physical testing setup is very similar from one hearable to another, it is necessary to understand how to wirelessly route the signal for your specific device.
There are no test standards specifically written for hearables, but since their practical use case, closely resembles headsets, the physical setup recommended by IEEE 269 [2] shown here is a good starting point.
SoundCheck includes a host of features to facilitate voice activation testing. These include:
- room acoustics measurements for calibrated room configuration
- the flexibility to create custom test stimuli including your wake word, Harvard sentences, or any other speech signal
- Sophisticated analysis options to allow you to analyze select parts of the test signal for analysis
- Active Speech level option
- Options to create calibrated background noise according to ETSI standards or custom background noise
Test configuration for hearing aid measurements on a hearable
Hearing Assistance
For hearables that function as “personal sound amplification products (PSAPs)” or essentially hearing aids, it is often necessary to measure their amplification or compression algorithms along with their corresponding attack and release times. This is usually measured according to the ANSI/IEC standard in an anechoic test box, where the loudspeaker is equalized to have a flat frequency response and the hearable is inserted into a 2cc coupler or “artificial ear”.The ANSI S3.22 standard [5] describes the method for testing hearing aids with AGC (automatic gain control) and could be applied to hearables that offer this functionality.
SoundCheck has been used for hearing aid testing for over 20 years, and contains all the functionality needed for custom PSAP testing as well as measuring to ANSI hearing aid standards..
Communications Tests
Where hearables are used as a communications device, for example as a headset with a phone, it’s often desirable to test the device to TIA or IEEE standards, or make measurements such as POLQA analysis for speech quality. SoundCheck has a long history in the communications testing space. SoundCheck contains all the functionality needed for communication testing such as active speech level, POLQA testing and test sequences for measurement to TIA and IEE standards, as well as Doubletalk and other communications tests. Please see the communications test section for detailed information.
Battery Life tests
Listen offers hardware and software for monitoring battery drain under various operating conditions.
Measurement to Standards
SoundCheck measures to a variety of standards that may be applicable to hearables. These include:
- IEC 60268-7: Sound system equipment – Part 7: Headphones and earphones
- EN 50332-1 Max SPL (European standard for max loudness)
- ANSI S3.22 Specification of hearing aid characteristics
- TIA 920.130: Telecommunications Communications Products Transmission
- ITU-T P.56 05/93 Method B: Active Speech Level
Watch a demo of hearables test
Video Demonstration of Hearables Testing
In this short video, Steve Temme demonstrates some of the tests outlined above – Bluetooth audio measurements and ANC tests – using perhaps the most common hearable in use today – the Apple Airpods.
SoundCheck Test Sequences for Measuring Hearables
Seqeunces from a wide variety of applications can be used for measuring hearables. Check out our complete Sequence Library
