Speech output

If the medium is speech the whole repertoire of learned vocabulary and meaning is exploited. In order to maintain a reasonable intelligibility the bandwidth should not be below three kHz, but higher bandwidth leads to a better quality. In a teleconference environment speech is generated by the participants, compressed, transmitted and uncompressed for presentation. Speech also can be used as interface machine-man interface. Recorded words or sentences can be played to inform the user about the status of the machine. Also information stored in textual form an be transformed into speech by the means of sophisticated synthesis algorithms. Hardware and software for this purpose is commercially available.

Another interesting application of speech is the use of speech inside of text documents. A lot of text editors offer to append non textual items like pictures and sound documents. Some tools for electronic mail support sound attachments, which might be a speech recording done by the sender. Some text editors allow to make annotations in text. At the position of the annotation an icon will appear. If the icon is activated either a textual or spoken annotation will appear.

Non-speech audio output

For non-speech output four main categories may be identified. Because in the recent literature the same terms are often used in different ways, first the definitions of the terms used in this report will be presented.

Auditory Icon

Everyday sounds that convey information about events in the computer or in remote environment by analogy with everyday sound-producing events [118]. Example:

• sound of a trashcan successful deletion of a file

• machine sound computer process running

Earcons

Tone-based symbol sets, wherein the verbal language is replaced with combinations of pitch and rhythmic structures each of which denotes something in the data or computer environment. They have language-like characteristics of rules and internal references [26]. Abstract, synthetic tones that can be used in structured combinations to create sound messages to represent parts of an interface [42].

Example:

• simple melody for indicating an error status

Sonification

Use of data to control a sound generator for the purpose of monitoring and the analysis of data. Examples:

• Mapping data to pitch, brightness, loudness, or spatial position [162]

• changes in bond market data changes of brightness of sound

Audification

A direct translation of a data waveform to the audible domain for the purpose of monitoring an comprehension. Example:

• listening to the waveforms of an electroencephalogram, seismogram, radio telescope data [162]

Sound spatialization

An individual sound can be filtered so that it appears to emanate from a specified direction when played by headphones. The filters simulate the distortion of the sound caused by the body, head, and pinna. Today fast DSP (digital signal processing) hardware allows real time filtering and dynamic updating of the filter properties, thus allowing interactive processes to be created for real time spatialization (e.g. allowing head movement and movment of virtual sources). The number of sound sources which can be presented simultaneously is limited by the processing capacity of the DSP-hardware. Presently available hardware like the Motorola 56001 can process two spatial sound sources in real time. Spatial sound is presently used in the auralization of models for room acoustics. Spatial sound gives an enhanced situational awareness and aids in the separation of different data streams (``Cocktail Party Effect''). Therefore, future applications could be in the fields of telerobotic control, air traffic control, data auralization and teleconferences.