Pre-computed Waveform Option

The "Pre-computed Waveform" is one of the Stimulus Type options available with the FF program. It allows the user to play waveforms that have been pre-computed and stored in a GW format file.

This option differs from the "General Waveform" option in the following significant ways:

In the "Gen. Waveform" option, a (user selected) general waveform is played after convolving with the appropriate transfer function for the point in space selected. In the "Pre-computed Waveform" option, the waveform is played out as-is, i.e. directly from the GW disc file. No correction or convolution is done for anything. This implies that the same waveform is played no matter what point in space the user clicks on.

The other main difference is that in the "Gen. Waveform" case, only one waveform can be specified for both ears. In the "Pre-computed Waveform" case, the user has the option of specifying separate waveforms for the left and right ears.

Using the Pre-computed Option

Before running the FF program, do the following:

(1) Compute and store the waveforms to be played in a GW format file. (Do not store more than 25 datasets in any one GW file). The FF program can work with upto 25 waveforms in any one GW file.

(2) It is recommended, though not required, that all waveforms for use with the FF program be stored in 16-bit format. This will use half the disc space as 32-bit format, and greatly speed up the FF program playback.

(3) Make sure the file name begins with FFGW (e.g. FFGWJUNK1.DAT). If not, then rename to a name that begins with FFGW. The FF program will not read GW files whose names don't begin with FFGW.

(4) Move the GW file to the D: directory on the server. For example:

        $ COPY FFGWJUNK1.DAT CORTEX::D:/LOG

The FF program looks for pre-computed waveforms in the D: directory of the server only. It will not find them on OPUS. The FF program will read a maximum of 25 files at a time. Do not place more than 25 files starting with FFGW in the server D: directory.

(5) Start the FF program and read below.

(6) Once the FF program has been started, and the main menu is on the screen, the first step is to select the proper GW file name (on the server D: directory). This is done by first clicking on the "STIM PARAMS" menu item, then on "GW File Name", and then clicking on the filename from the list of files that pops up. (Note: The FF program displays a "short form" of the file names in order to conserve space. This means that it does not display the FFGW at the beginning nor the .DAT at the end. The full file name is however still used and required for all other purposes.)

(7) Next, select "STIM TYPE" from the main menu, then click on "Pre-Computed Waveform", then select (in order) the Left-ear and Right-ear waveforms by clicking on the list of ID's that pops up. Note that the waveform ID's are recorded on the terminal window (and in the disc log file). To play the same waveform from the left and right ears, simply click on the same DSID twice.

(8) Finally, to play the waveforms and collect data, click anywhere on the virtual space grid and listen to the waveforms. The waveforms played in this mode are independent of where in space you click.

(9) To change the waveforms being played, just click once on the "Pre-Computed Waveform" button and the list of DSID's pops up again, letting you select another waveform(s).