Self fitting
WIP: This article is still work-in-progress
The prototype can also be controlled from a remote PC, e.g., a laptop with touchscreen, in a more interactive way than it is possible with the openMHA fitting GUI or the bluetooth controller.
Since version 1.2 of the SD-card image, a script which queues commands from the network started on boot. It allows to easily toggle/set actions/variables from a remote PC and design a more interactive user interface for a self-fitting experience.
An example is implemented in Octave
The example code requires netcat and sends the commands to 127.0.0.1 port 33338.
In order to pass the commands to the prototype you need to forward the local port 33338 to the prototype, i.e., connect with ssh -L33338:localhost:33338 pi@172.24.1.1 under Linux, and run at least version 1.2 of the SD-card image on the prototype.
The example GUI allows to provide individual frequency-dependent hearing thresholds for the left and right ear, where the levels are interpreted at the microphone of the device. The toy prescription rule is then used to calculate a gain table depending on the threshold and the position of the sliders. To activate amplification check the "amplification" checkbox.
The sliders should be intuitive to use and invite to play around. For a description of their effect, please have a look at the source code. The figures illustrate the frequency-dependent amplification and compression. Estimated hearing thresholds for listeners with normal hearing are indicated for orientation with the dashed black line.
The "feedback" button allows to trigger the feedback path estimation, which can be helpful if feedback becomes audible and limits amplification
Input signals from the microphones can be turned off with the "live" checkbox. Input can be recorded with the record button, where each click will queue a 10s recording. There is no indication if the recording is active, please wait 10 seconds after pressing the "record"-button before you continue.
The last recorded signal can be played back with the "playback" drop-down menu. Also, since version 2.0 included in the SD-card image, a selection of recordings is available for playback which can help to test the configuration in different acoustic conditions. The number triplet approximately indicates the maximum, the median, and the minimum levels in dB SPL.
A threshold simulating noise can be activated which roughly results in elevated hearing thresholds similar to those indicated by the black line in the figure, which is the defaut configuration. For users with normal hearing, this allows to "simulate" impaired hearing with the threshold simulating noise and to experience a benefit from the provided amplification.
The calibration checkbox allows to disable the input and output compensation filters in order to get an impression of their effect.