Detailed quick start

This page is supposed to give a more detailed start instruction than given in "Home-Wiki". Here, we explain how connect the graphical user interface (mhacontrol) to the hearing device. There is also an explanation on how to perform or check the calibration of your device.

Setup

1. At first download the image in "Home-Wiki" under "Image download".
2. Use i.e. the program "Etcher" to put the image to your SD-card. Then put the SD-card in your Raspberry-Pi.
3. Turn fully to the right all knobs of the sound card.
4. Connect the hardware according to the image in "Home-Wiki". Make sure that you are not wearing the headphones!
5. As soon as you connect the Raspberry-Pi to the Battery, it will start to boot. The first boot takes a bit longer.
6. Try carefully if the loudspeakers of the headphones produce sound.
7. Carefully plug-in the in-ear headphones
8. Take out the headphones immediately if you feel uncomfortable
9. Experience an altered perception of sound

Connect the mhacontrol GUI

After you have done the general setup of the hearing aid prototype, you are supposed to hear basically what you hear without the device. In the best case the device would be acoustically transparent. OpenMHA comes with a graphical configuration tool which can also be used for fitting and calibration.

In the following the installation of that user interface will be explained:

1. First download the github repository "HoerTech-gGmbH / openMHA"
2. Connect to the wifi-network "openMHA-wifi" with default wifi-password "openmha-wifi".
3. Download the program "PuTTY" to connect with the prototype. Start Putty and set "Hostname" to "172.24.1.1" and "Port" to "22". Then open the category "SSH" in the Putty configuration window. There choose the category "Tunnels". Here set the "Source port" to "33337" and the "Destination" to "localhost:33337" and click "Add". You can store your PuTTY session to be able to reload it the next time.
4. Putty opens a terminal window. There use the username "pi" and the default password "openmha". Now you are in remote control to the Raspberry-Pi.
5. Using GNU/Octave (or Matlab) enter the subdirectory of the downloaded openMHA-master/mha/tools/mfiles.
   a) Using GNU/Octave, make sure you have a working Java Runtime Environment (JRE). For example, on Windows 10 the combination of Java SE Runtime Environment 8u161 (http://www.oracle.com/technetwork/java/javase/downloads/jre8-downloads-2133155.html -> jre-8u161-windows-x64.exe) and Octave 4.2.1 works fine.
   b) Using Matlab, a JRE is already included.
6. Edit the file "mhacontrol.m" and comment out the lines 55-57 adding " % " to the beginning of those lines. (this will prevent mhacontrol from resetting your calibration, only needs to be performed once)
7. Add the java library with javaaddpath mhactl_java.jar.
8. Now run mhacontrol with mhacontrol.

Ad-hoc calibration

Please read Calibration before proceeding. The software on the SD-card image in the latest version (since 0.5) provides a good calibration for the reference hardware.

1. To do the calibration now, press actionbar "Fitting" in the MHA control GUI, which just opened through GNU/Octave (or Matlab). Here select "flat 40" and press "OK".
2. In the upcoming window "MHA fitting tool" select "nogain" in "Gain prescription rule" and in "Presets". This setting is needed to do the calibration, because with nogain no frequencies are amplified. Later you can select other hearing aid algorithms here, which you should recognize in a different sound perception. The change of hearing aid algorithm will not be saved after rebooting.
3. Now open "Levels" in the MHA control. Ask someone to talk normally and continuously in a quiet environment and read out the internal levels at a distance of 1 meter. Here it can help to select the 2 second averaging.
4. The internal levels in this situation are supposed to be around 65 dB. Calculate the difference of the internal levels shown in the GUI to 65 dB. I.e.: While somebody is speaking in that 1 m distance, the internal levels are around 55 dB. So the difference to 65 db is 10 dB.
5. Now use the remote access of putty. Type cd hearingaid-prototype to open this folder. Here do nano openMHA.cfg to open the configuration of openMHA with a text editor.
6. Scroll to the entry "mha.calib_in.peaklevel" and change the given values by adding the calculated difference (i.e. those 10 dB). Save with Ctrl-O and close with Ctrl-X.
7. After doing this, reboot the Pi with sudo reboot.
8. To improve the calibration further find now a noisy environment, like a hair dryer, microwave oven or a vacuum cleaner.
9. To calibrate the output, configure now "mha.calib_out.peaklevel" in the same folder such that the perceived loudness is similar when hearing with the hearing aid prototype and without it.