2
Signal Formats
Before pictures and music or voice and web pages can appear, the source information must be captured using some form of transducer (e.g., a microphone or video camera) or application software and what results must be turned into a digital signal that can be processed and probably mixed (multiplexed) with other digital signals. They form a digital stream that is transmitted across a network to be distributed and reconverted to original form at the user’s receiving equipment. In this chapter I describe the transformation of voice, video, and data information for its transmission across the network.
When speaking, we create a surprising range of sounds and they provoke a rich range of responses. When converted to an electrical signal by a transducer, such as the microphone in a telephone, this vocal energy is converted to an analog signal. At other times, personal communication employs shapes drawn in various ways on paper, still pictures using shades of gray or colors, and pictures shown rapidly in sequence to give an impression of motion. To achieve communication at a distance, these artifacts must be converted to forms that can be processed by digital machines, and, to achieve triple-play, the ways in which they are represented should be such that delivery of voice, video, and data can be made over the same connection.
To conserve bandwidth and storage space, the quantity of data used to represent the processed signals should be minimized. This is achieved by ...
