User:Maxim.porhun/sandbox

"Petralex" is a hearing aid application for smartphones and tablets that implements a digital hearing aid with a built-in in situ-audiometry procedure. This application takes into account the ambient sound environment and independently adjusts to the user's ear. Petralex was developed by IT4YOU corporation for smartphones and tablets with Android and iOS operating systems and is distributed free of charge through the Donationware system.

Development history
Petralex hearing aid application development was started in July 2012. It was originally planned to test the computational facilities of the iPhone 3G S platform based on iOS for the implementation of a signal processing system that performs a hearing correction scheme for sensorineural hearing loss.

In February 2014, at the time of publication of the first Petralex version in the AppStore for smartphones starting with iPhone 4 and later, the application included a binaural hearing correction system that performs audio signal processing separately for the left and right ears. This system is implemented using headphones or a headset that are compatible with the iPhone 4 with newer devices. Also in Petralex 1.0, a dynamic range compression system was implemented. This system has the option to customize the gain formula of the following:


 * Petralex;
 * NAL-R;
 * Berger;
 * Pogo.

After the successful implementation of Petralex on iPhone, on April 6, 2014, a version of the iPad application was released.

In application version 1.3.0, released on June 16, 2014, the possibility of using wireless bluetooth headphones and headsets has been dropped, the interface has been updated, and the option of acoustic feedback suppression has been added.

From that time to the present, Petralex development team continues to improve the application by adding new features and improving algorithms.

Basic principles of work
Petralex basic principles of work, like most of hearing aid applications, are similar to those of traditional hearing aids.

Petralex implements two modes: setup mode and hearing correction mode.

Setup mode represents hearing test using in situ-audiometry procedure. This mode allows the user to measure his hearing thresholds for both ears separately using tone audio signals of different frequencies from 125 Hz to 8000 Hz.

Hearing correction mode represents an audio signal processing system, which implements a broadband (without subband decomposition) signal processing scheme. This scheme uses broadband method for changing the correction of the spectral envelope of a signal using a filter with a finite impulse response. FIR filter frequency response is based on the user's hearing thresholds: amplification performed of those frequencies that the user hears worse. Petralex general signal processing scheme (figure 1) corresponds to the hearing aid application general scheme.

Input audio signal, acoustic feedback (echo) and background noise are captured by the microphone, summed and then divided into subbands using an analysis filter bank, which decomposes this signal into perceptually matched subband components. Then, subband signals passes threw the following blocks: noise reduction, acoustic feedback cancellation and hearing loss compensation. Noise reduction block implements noise reduction algorithm based on the psychoacoustically motivated spectral weighting rule. Acoustic feedback cancellation block implements the normalized adaptive least-mean-square algorithm. Hearing loss compensation block implements frequency dependent signal attuneation, based on the users hearing thresholds as a result of the in situ-audiometry. This block also performs dynamic range compression, which compensates non-linear amplification of the human cochlea. Output signal is synthesized from subbands using synthesis filter bank.

User also can change the total loudness threw the applicatiob interface to adjust the most comfortable listening level.

Comparison with traditional hearing aids
Comparison characteristics between Petralex hearing aid application and traditional hearing aids are presented on the following table:

Features
Petralex application key fetures are:


 * In-built hearing test;
 * Automatic adjustment of the application without a audiologist's help;
 * Remote adjustment: application can be finely adjusted remotely by a specialist;
 * Audio recorder;
 * Speech recognition (automatic conversion of the recorded speech into text);
 * Regulated noise suppression;
 * Ecosystem;
 * In-built adaptation course;
 * Dynamic range compression;
 * Using application with different headphones/headsets.

Ecosystem
Four mobile applications (Petralex, Video Volume Booster, Radio Volume Booster and Music Volume Booster) form a single ecosystem. Hearing profile from Petralex can be used to setup additional applications, which provide user for listening to music, radio and video with amplified sound, adapted to the users hearing. Basic principles of work of these applications are similar to Petralex: the sound is amplified at those frequencies at which the user hears worse.

International cooperation
In 2019 Petralex hearing aid application was implemented for subscribers of a leading telecommunication services provider in Sri Lanka - Dialog Axiata. This will allow users to utilise their smartphones with headset as a hearing enhancement tool, thereby making it an affordable and accessible solution.

Scientific value
Petralex hearing aid application often mentioned in different scienific publications:


 * 2016: Information technology and telecommunications.


 * 2017:
 * Academy of doctors of audiology.
 * Education and Information Technologies.
 * Modern Fuzzy Control Systems and Its Applications.
 * Signal Processing: Algorithms, Architectures, Arrangements, and Applications (SPA).


 * 2018: American Journal of Audiology.

Awards
Since the first release Petralex has been awarded several awards:


 * 2014 - the PC Magazine edited the Petralex application for the "Best Soft 2014" award, recognizing this application as the best hearing aid that implements on a smartphone.
 * 2016 - The best learning Program – virtual learning for people with hearing impairs.
 * 2017 - winner of the Microsoft Inspire P2P contest.
 * 2018 - silver winner of the Microsoft Inspire P2P contest.