Manual Audiogram

Here is the manual to determine the pure-threshold audiogram for the experimental setup at the department of Biophysics at the Donders Institute for Brain, Cognition and Behaviour.

 

Cables

 

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The audiogram-program makes use of TDT's RP2 and PA5 modules. Make sure that everything is connected as shown above. Use the Bose QC-2 headphone. There are alternative headphones available at the department such as the TDH-39 and Sennheiser PCX350; the TDH-39 is also used in the clinic for their audiograms. However, the Bose usually suffices, and has flatter speaker characteristics for higher (>4 kHz) frequencies than the TDH-39.

Run the experiment

In Matlab, run:

 Audiogram

This should open the following graphical user interface (GUI):

Then do the following steps

  1. You should initialize the TDT (press Initialize).
  2. Seat the subject
  3. Subject should put on the headphones
  4. Give button to subject
  5. Instruct the subject to press the button as soon as he/she hears a tone.
  6. Close the door
  7. Run (press Run)

The experiment will now run. The program will automatically determine the subject's pure-tone threshold for several frequencies (usually: 125, 250, 500, 1000, 2000, 3000, 4000, 6000, 8000, 12000 and 16000 Hz).

 

Analysis

The data can be analysed with:

pa_tdt_bose_audiogram

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Conclusion

Based on these simple audiograms, we can exclude or include subjects. Everyone with a threshold larger than 20 dBA at any of the tested frequencies below 10 kHz should be excluded for any study involving normal-hearing subjects (for patients, the clincially-derived audiograms should be used).

Default vs Custom

Usually, the default settings will suffice. Below, the software and hardware is described in more detail, if you ever need to adjust some parameters. Whenever you adjust things, save the files with different names than the default files!

Hardware

We use a Bose Quiet Comfort 2 headphone. The sound level in dBA per sound frequency at a given attenuation provided by the PA4 is shown in figure 3.

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These measurements were determined by a Bruel & Kjaer with the headphone on a kemar-head. The calibration can be analysed with:

pa_bose_qc2_calibration

 

Conventions

The data are (crudely) calibrated to dB HL (Hearing Level) by

pa_dba2dbhl

However, there are several different HL standards available on the web, none of which say anything about high frequencies (>8 kHz). This yields discrepancies, as can be seen in the following figure.

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Matlab

All m-files required for the experiment are located on the experimental computer of the 2nd human-sound-lab at C:\MATLAB\Audiogram, and can also be found in the PandA google code trunk. The easiest way to use different settings is to change the configuration file AudiogramCFG.mat. This can be done in Matlab with the m-file AudioCFG.m.

Here is the code for the audiogram.

RPvdsEx

The rco file used by Audiogram.m is located at C:\MATLAB\Audiogram\RpvsdEX\RP2.rco. The RPvdsEx file looks like this:

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