The FTW Transcriber’s speed control section, indicated by the black arrow, enables you to increase or decrease the speed of playback. You can do this either by dragging the slider with your mouse or by using hotkeys. By default, the 8 key on your numeric keypad increases speed, and the 2 key on your numeric keypad decreases speed.
Under the slider is a box containing the number 50 by default, and a “set” button. This is your alternative playback speed. Enter a figure between 25 and 250, then click “set”, then use the 5 key on your numeric keypad to toggle back and forth between that speed and 100. This is useful if you want to quickly change the playback speed temporarily to try to make out a difficult word when transcribing.
If NUMPAD 5 appears not to work, this may be because it is disabled by default. To enable it, click Settings, Keyboard Shortcuts, and uncheck the appropriate box/es.