Android is a cellular phone operation system that has been launched by the open headset alliance and Google Inc in late 2007. The underlying software stack is open source and the a first version of the API is public since November 2007.

The AmpliCell application allows the phones user to enter his audiogram data, select an appropriate fitting rule and do some adjustments of the gain and the non-linear properties of the signal processing – much like the fine tuning of hearing aids. It also allows to activate or deactivate the virtual hearing aid in the cellular phone.

The AmpliPlay application is a media player that exploits a virtual hearing aid. This software accesses the individual amplification needs as collected by the AmpliCell application, retrieves properties of the media to be reproduced (sample rate, bits per sample, mono/stereo), creates a virtual hearing aid that is capable of processing the media at hand, does the actual signal processing and plays the processed signal to the phones user.

Software architecture

We envision the following architecture:
This is our aim: Block diagram of the signal flow in a mobile phone with AmpliCell.

However, as of today, we are facing the following limitations:

Limitation: Signal processing is slow in the emulator.

Solution: As soon as we are able to test AmpliCell on real hardware, we will start optimizing the signal processing for higher speed and lower power consumption. We are confident that processing speed will not be an issue in modern mobile phones. Hearing impaired users that are willing to spend several thousands of dollars for a pair of digital hearing aids are probably willing to purchase a mobile phone with a fast processor and headsets with sufficient output sound pressure level.

Limitation: Version M5 of the Android SDK does not allow to access the audio samples of decoded media content (such as MP3 files).

Solution: We are confident that future versions of the SDK will allow AmpliCell to access the decoded audio samples of all media content.

Limitation: Version M5 of the Android SDK does not allow to access the audio signal of the GSM signal.

Solution: As soon as this becomes possible in at least some mobile phones, AmpliCell will be able to unfold its true potential and make phone calls more intelligible for hearing impaired listeners.

Given these limitations, an AmpliCell based software hearing aid can not yet run as an Android service in the background. Instead, we have implemented the following proof of concept architecture:

Proof of concept architecture (as submitted to the contest)

The proof of concept architecture needs to introduce the AmpliPlay application as an interim solution to play wave files. In the final architecture, this application will not be needed any longer, since AmpliCell - if enabled by the user - will process all audio signals in a background service.

NB: The final application will automatically detect the presence and usage of mono or stereo bluetooth headsets and display the tone slider accordingly. It will also allow to configure on which side the user holds the phone to his ear.