Hearables Amplify Benefits for Audio Apps

By Phil Hipol for Mouser Electronics

Hearables Amplify Benefits for Audio Apps

Numerous wearable technology products have been introduced in recent years that integrate smart electronics into accessories like watches, various clothing fabrics, or even subcutaneous implants. Many of these wearable technology products are capable of connecting to computer networks, enabling data to be exchanged between the network and the device, then analyzed. Wearable technology has gained market traction in devices such as smartphones and smartwatches that integrate computers, wireless networks, and communication devices together with a variety of miniaturized sensors and transducers. These wearable devices enable applications such as mobile communication, activity monitoring (e.g., fitness and sleep), biometric measurement (e.g., heart rate, temperature, and oxygen consumption), navigation, and geolocation.

Hearable technology is a rapidly-growing subset of wearable technology, which might eclipse wearable technology in upcoming years. A typical hearable device is configured like a standard hearing aid and is placed into a user’s ear. Some hearable devices are custom-molded to the user’s ears to enable a form-fit and to provide passive sound isolation—like ear plugs—to prevent unwanted noise from entering the ear. Hearables use one or more microphones to receive sound from the outside world, as well as a microcomputer to process sound. The processed sound is then output to amplifiers that drive loudspeakers in the ear canal. Some hearables can be connected to a mobile phone that can provide the display and user interface needed to interact with the hearable device. 

Hearables offer several advantages over many wearables:

They are discrete rather than bulky and carry a lower risk of being dropped and breaking.They contour to the ear in such a manner that they may appear invisible to others.Their close proximity to the ear enables them to more accurately detect biometric information.Their detection and modulation of sound provides several useful and innovative applications in the areas of audio enhancement, wireless connectivity, biometric monitoring, and communications.

This article examines the applications for wearables to enhance audio applications.

Hearing Is Believing

The human ear is a sophisticated sensory transduction device that can convert sound waves (or pressure fluctuations) in the air into nerve impulses or electrical signals in the brain. The ears have an incredible dynamic range of up to 120dB, which is a factor of one trillion times the sound power between the lowest detectable and highest allowable sound levels. They can also detect this sound in a wide frequency range, from about 20Hz up to 20kHz. Another important property of the ears is that they are capable of sound localization, which is the detection of the origin and direction of sound. This is enabled because the brain can sense very slight differences in the magnitude and phase of sound pressure waves as they travel from one ear to the other.

Ears can process information much faster than the eyes, taking only 1/1000th of a second for a person to process auditory data compared to 1/50th of a second for processing visual data. Once a sound wave reaches the ear, the brain can recognize it in just 0.05s, which is 10 times faster than the blink of an eye. It takes about 0.2s for your brain to understand the light that reaches your eye or to recognize something touching your hand or foot. It is believed that our sense of hearing is so fast because hearing quickly helped our prehistoric ancestors when they couldn’t see at night, when hearing and detecting potential threats meant the difference between life and death. 

Hearable Audio Applications

Hearables take advantage of these remarkable properties of the ears to provide significant audio enhancements in numerous application areas:

Sound amplificationFrequency equalization and filteringAudio maskingAudio effectsActive noise cancellationDirectional hearingAudio analysisSound Amplification

One of the basic functions of an in-ear device is to amplify sounds from the outside world to enhance hearing and to allow other devices like television sets to broadcast at lower volume levels so as not to disturb other individuals. Hearing aids have traditionally been used in such applications; however, they are medical devices that are regulated by the FDA, whereby the user must first be seen by an audiologist who performs tests to identify which frequency bands require amplification, among other things.

Hearables, including Personal Sound Amplification Products (PSAPs), can be used to amplify sound in a manner similar to hearing aids. These devices do not require a prescription and can, therefore, be purchased over-the-counter at a lower price than hearing aids. Used in this manner, both hearables and PSAPs will typically amplify all frequency bands equally across the hearing spectrum.

Frequency Equalization And Filtering

A more advanced capability of hearables is selective filtering of incoming sound waves, enabling the user to focus on desired frequencies only. This capability, known as equalization, allows the user to attenuate (reduce) or amplify (boost) sound in certain frequency ranges or bands. Two types of equalization can be used:

Graphic equalization is a simple type of equalization that affects sound only in certain fixed frequency bands.Parametric equalization, a more sophisticated type of equalization, that affects sound at specific frequencies in variable bandwidths.

For example, noise within an airline cabin might be rich in low-frequency “humming” from the engines and high-frequency “whirring” caused by air turbulence. An effective equalization of this noise may involve attenuating in the low- and high-frequency bands, and amplifying in the mid-frequency ranges to enhance speech intelligibility.

Audio Masking

Hearables can incorporate white or pink noise generators, which are typically used by individuals to drown out annoying background noise to enhance concentration, relaxation, or sleep. In many cases, broad spectrum sounds from nature—such as rainfall, the rustling of the wind, birds chirping, or ocean waves—are used as an alternative to the “electronic static” sound of white noise. Medical research has also determined that the use of audio masking is an effective means of providing “sound therapy” or relief for individuals with tinnitus (a malady resulting in “ringing” in the ears) to cover the sound and decrease their perception of it.

Audio Effects

Hearables can be used to greatly enhance listening to music in real time by adding audio effects, such as flanging/phasing, delay/echo, reverb, and chorus, among others. For example, listening to music in a small confined space can be made to sound like listening to music in a large concert hall by use of reverb and delay. Other effects like 3-D sound can be used on recorded audio, where the hearable loudspeakers work together with accelerometers and position sensors within the hearable device to give the impression of a 3-D sound field. Here, sound would appear to emanate from different distances above, below, in front of, and in back of the listener, and would change in intensity as the listener moves around the room or turns his head. These 3-D sound features may work well together with virtual reality gaming systems.

Active Noise Canceling

Unlike filtering, where all of the sounds in a certain frequency band are attenuated, Active Noise Cancellation (ANC) is capable of selectively eliminating certain sounds that occur in a narrower frequency range. ANC involves the use of one or more outward facing microphones that capture the incident sound. A digital signal processor then examines the sound waves to detect (usually periodic) noise components. It then calculates the magnitude and phase of the required sound waves to destructively interfere, or cancel, the sound (i.e., the so-called “anti-noise”). A loudspeaker, which is positioned downstream of the microphone, then broadcasts the anti-noise towards the eardrum, and the noise is cancelled prior to reaching the eardrum. 

While it is easy to see how ANC can be useful to eliminate unwanted noise that is a nuisance in everyday life, ANC hearables may find an expanded role in regards to enhancing workplace safety. Many workers are subject to extremely loud noise levels that currently require passive ear plugs; however, the ear plugs also reduce desired sound from coworkers, public address systems, warning devices on vehicles, and other moving machinery. It is envisioned that a workplace hearable can use a combination of passive sound attenuation (through the body of the device) together with active noise cancelation to eliminate periodic background noise. Worker-to-worker, as well as machine-to-worker communication, can be accomplished through the hearable’s built-in wireless network, communications, microphones, and loudspeaker devices. Working together, these passive, active, and communications components can reduce worker hearing loss, enhance communication, and improve worker safety.

Directional Hearing

Hearables can be outfitted with arrays of directional microphones that will enable the user to control the focus or spatial location of the microphone center so that all other sounds outside of the focus are blocked. This capability, known as acoustic beamforming, enables one-on-one conversations in very loud environments with numerous sound sources. Beamforming also allows the user to discern certain sounds from within a complex sound field. Acoustic beam microphones are currently used in television broadcasts where background noise is loud (such as sporting events) to pick up the voice of an announcer or player(s) on the field.

Audio Analysis

Microphone signals from the hearable device can be recorded and transmitted wirelessly to a computer platform for later acoustical analyses and signal processing. For example, it can allow mechanics, technicians, and other service personnel to quickly identify mechanical anomalies on operating equipment, or it can enable doctors and nurses to quickly identify anomalies when listening to a patient’s breathing or heartbeat patterns.

Hearable Technology Components

Mouser’s extensive product offering includes semiconductors, interconnects, passives, and electromechanical components, many of which enable hearable technology. Some examples include the following products:

PUI Audio Microphones with 100mm Leads are designed to make product prototyping, PCB design and layout, and assembly tremendously faster. PUI Audio Microphones with 100mm Leads indicate polarity by color on the halogen-free UL3302 32 AWG wire, virtually eliminating accidental reverse polarity connections. This line of microphones is based on popular 4mm, 6mm, and 9mm models that were previously only offered with solder pads.

PUI Audio PMM-3738-VM1010-R is a low-noise, single-ended analog piezoelectric MEMS microphone with wake-on-sound. The PMM-3738-VM1010-R with Vesper technology is the world's first ZeroPower Listening™ piezoelectric MEMS microphone and is designed for an ultra-low power, always-listening solution delivering voice activation to battery powered devices. Features include full audio output on wake-up, dust and moisture resistance, and an extended battery life up to 10x.

Microchip's RN52 Bluetooth® audio module provides a fully integrated solution for delivering high-quality stereo audio in a small form factor. Microchip's RN52 Bluetooth audio module combines a Class 2 Bluetooth radio with an embedded DSP processor, controlled and configured by simple ASCII commands and GPIO. It integrates RF, a baseband controller, and DSP, making it a complete Bluetooth audio wireless link. The RN52 supports HFP/HSP, A2DP, AVRCP, SPP, and iAP profiles, and it includes support for codecs such as SBC, aptX®, and AAC. It also provides a UART interface, GPIO, stereo speaker outputs, stereo microphone inputs, and a USB port.

For the multi-protocol wireless platform, Mouser offers the SparkFun ESP32 & ESP8266 Things, which are the perfect foundation for Internet of Things (IoT) projects. The Things do everything from turning on an LED to posting data with phant.io and can be programmed like any microcontroller. The Things can even be programmed through the Arduino IDE by installing the ESP32 Arduino Core.

Mouser also offers the Samsung ARTIK Modules, which are pre-certified IoT modules that are ready to integrate with the ARTIK Cloud, reducing time-to-market. Samsung designed this diverse range of modules to drive IoT products. From the the most basic applications to controlling/monitoring hubs, there’s an ARTIK module suited for any application. The modules are divided into families based on size, power, and capabilities, which support BLE (Bluetooth Low Energy) Wi-Fi, I2S, and DSP.

Conclusion

A rapidly growing subset of wearable technology known as “hearables” has potential to significantly change our lives in regards to mobile connectivity, audio enhancement, biometric monitoring, and communications. The applications for hearables in the audio and entertainment field are numerous and are continuing to evolve. We will likely see an increasing number of users adopting hearable technology, together with a growing number of products and applications that are being developed to satisfy consumer needs. Hearables are enabled by miniaturized electronics, such as sensors, transducers, amplifiers, network communications, and microprocessors. Mouser Electronics is committed to supplying product developers with these state-of-the-art components to make hearables an everyday reality.

Mr. Phil Hipol has more than 30 years of experience in the field of noise and vibration analysis, testing and control in several industries. He has an MS in Engineering and has published original research in the field of vibro-acoustics, where some of his work appears in the industry-standard Shock and Vibration Handbook and the NASA Handbook for Dynamic Environmental Criteria. Mr. Hipol has invented numerous devices and is co-inventor of an award-winning novel acoustic device, the catheter stethoscope, which non-invasively monitors the fetal and maternal heart rates and maternal contractions during labor and delivery. He has also worked extensively in the field of active and passive noise and vibration control, and has implemented numerous sound and vibration attenuation solutions for industrial, commercial, residential, and biomedical applications. Mr. Hipol is skilled in the use of state-of-the-art sound level meters, dynamic signal analyzers, microphones, accelerometers and acoustic cameras, as well as the use of various industry-standard noise and vibration analysis and simulation software.

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