Chapter 6: User Interfaces for Mobile Media 219 • 1024 × 768 pixels (XGA) is a typical resolution used in current mainstream laptop computers. There are also more primitive ways of conveying visual information. LEDs, for instance, are used for providing simple feedback related to the device state, such as battery level that can be indicated with dif- ferent colours or frequency of fl ashing. Audio output can be divided roughly into two categories: speech and non-speech. Speech output is based on text-to-speech synthesis, or playing fi les that contain speech. Text-to-speech (TTS) synthesis is used, among others, in the Nokia N91 multimedia com- puter for playing recognized voice commands, or speaking aloud the caller’s name. Several devices are capable of producing mono- or polyphonic tones and playback audio fi les, which make the use of audio versatile and appealing. Notifying the user about an event or providing feedback on operations, such as key presses, are typical examples of using non- speech audio output. A prominent difference between mobile and desktop UIs is the use of vibration as an output modality. In desktop computers, vibration (for 7 example, via a vibrating mouse) has not gained popularity. However, phones using vibration for notifying, for instance, about an incoming call have more appeal. The benefi t of tactile feedback is that in a noisy and busy environment the user does not have to pay attention to the device constantly, but may place it in pocket and only take a closer look on sensing vibration. A central concept related to output is feedback that refers to the system’s response to the user’s action. It can be based on one or more modalities. For example, when the user is typing text by pressing the keypad, the key press is indicated with a small audio beep while the typed characters and the cursor position are displayed on the screen. In addition, each action that the user performs should give feedback in some way. For frequent actions, the feedback should be subtle so as not to disturb the task fl ow. Feedback is also something that users will appreciate when interrupted by something sudden and unexpected. 6.3.3.2 Input As the mobile UIs are descendants of graphical WIMP user interfaces, the input devices related to pointing, selecting, and entering text are the most relevant. 7 Currently the only domain in desktop computing where the vibration is used is in gaming with the devices, such as racing wheels and joystick with force feedback.