Description

This program was initially written to demonstrate the principle of psychoacoustic tuning curves (PTCs). Since it's inception it has been used by several people in experimental studies - the programme has been used to obtain PTCs on children as young as 6 years old. The principle behind a PTC is that the listener has to detect a tonal signal that is near threshold (e.g. 10 dB SL). A masker (narrow-band noise) is then introduced and the level of the masker is adjusted so that the tone is just audible above the masker (masked threshold). Maskers away from the tone frequency are less effective and thus need to be more intense to mask the tone. As the masker frequency is swept from below to above the tone frequency a classic "V" shaped PTC can be produced.

Traditionally PTCs are measured with the masker presented at discrete frequencies and the masked threshold obtained at each masker frequency. These are then plotted to produce a PTC. This software uses a type of "Bekesy" tracking to continuously sweep the masker across the frequency range. The general outline of the software is given below.

The software consists of a main interface (fig. 1) which allows the parameters to be adjusted. However, the program is loads all the parameters from a .ini file which must have all the appropriate bits in it. An example of an .ini file is given in the zip archive of the program and an annotated version can be found here: PTC-software.ini

Once the .ini file has been loaded the parameters can be adjusted if necessary (but better to change the .ini file). You can also step through the list of conditions using the arrows on the interface.

The calibration button allows the system to be calibrated. The general principle is that in the calibration routine (fig. 2) the attenuators (either software or hardware) is set to zero (i.e. max. output) and a sinusoid is played out that can be measured appropriately. The hardware is then adjusted appropriately to give the correct output - it is important to remember, that when using the software attenuation the dynamic range is limited by the 16-bit scaling within the software and the limitations of the sound card (24-bit scaling is on my todo list).

Once Calibrated and the tone level is set - the test can begin. Press the "Run PTC" button and the following screen will appear (fig. 3). Read the instructions on the screen and click on the start button. The general principle is: press the "space bar" when you can hear the tone - let go when you can't (if you have a programmable game-pad, or joystick you can set one of the triggers to "space" to make the task easier and usually quieter). If you want to stop the test at any time, just press any other key and follow the instructions.

The output of the program is available in two forms. Firstly, you can look at a plot of the PTC immediatly after it has been obtained (this can also be printed, or copied as an image). An example of this output from the sofware can be seen in fig 4 . However, once a new PTC is started, this is overwritten. The second output is into a .dat file (see example) . Which stores the raw data in from the PTC. When a new PTC is run the file is appended to. The file name can be changed by typing in the name into the main screen's "Results File Name" box.