Digital audio: examples of the application of the ASP integrated signal processor

Electronic processing of audio signals is not new. Tone control by means of one or more analog filter stages is a well-known example from hi-fi technology the technology of the faithful reproduetion of speech and music. Another example is the improvement of audio quality by altering spatial perception with the aid of stereo effects and reverberation. The basic knowledge of acoustics and perception required here has long been available, but until now many practical applications have been restricted to professional use in the studio, e.g. for records, radio, TV and film. However, great changes are on the way, for we are now in the digital age of audio technology, and this includes equipment for the 'ordinary' consumer. For the best results, sound is now recorded in digital form on tape or disc (the Compact Disc [11). This can be done virtually without distortion and with signal-tonoise ratios previously thought impossible. From digital recording to digital processing is but a single step. All the advantages of digital signal processing [21 are then assured. With digital methods it is easy to make an ideal memory. This is of primary importance for audio technology, for signals can then be delayed as desired. Another important feature is that processing, once selected, remains fixed and immutable for example, feedforward controls always remain stable, even in the long term. On the other hand, various settings of the equipment are easy to change automatically by digital methods ('adaptive control'), so that an optimum result is always obtained by an appropriate selfadjustment. For the listener, the introduetion of digital signal processing in audio [31 provides a number of new facilities that were previously too expensive or technically too difficult, such as: • Dynamic-range compression or expansion reducing or increasing the difference between the levels of loud and soft passages as required.