James A. Moorer

The Lucasfilm audio signal processor

The requirements of audio processing for motion pictures present several special problems that both make digital processing of audio very desirable and relatively difficult. The difficulties can be summarized as follows: (1) Large amounts of numerical computation are required, on the order of 2 million integer multiply-adds per second per channel of audio, for some number of channels. (2) The exact processing involved changes in real time but must not interrupt the flow of audio data. (3) Large amounts of input/output capacity is necessary, simultaneous with numerical calculation and changes to the running program, on the order of 1.6 million bits per second per channel of audio. To this end, the digital audio group at Lucasfilm is building a number of audio signal processors the architecture of which reflects the special problems of audio.

A distributed computer system for professional audio

In professional audio, the transition from analog to digital technology is nearly complete. The more recent shift towards systems based on general-purpose computers has been gradual, because such computers lack the processing and I/O performance needed for professional audio applications. The SonicSystem, a professional digital audio system, solves these problems using DSPs and a specialized file system. We describe the uses and implementation of the SonicSystem. A distributed version of the SonicSystem, using FDDI networking, was released in 1992. It provides transparent real-time access to remote sound files, and can handle 100 or more CD-rate channels simultaneously. The system provides guaranteed performance: an activity (such as playing a sound file) is permitted to start only if it can be assured of completing with no dropouts. These properties are achieved by the use of a special-purpose transport protocol, real-time scheduling, and resource reservation.

SoundDroid: A New System for Electronic Post-Production of Sound

Sound Droid is a system with sophisticated sound editing capabilities, which provides eight channels of mixing in its minimal configuration. Sounds are stored on magnetic disk, and can be played back at any time and in any sequence. The fluidity of “soft” cuts encourages creative experimentation, and all sound manipulations are automatically memorized. Being all-digital, Sound Droid eliminates distortion and generation loss in audio processing while providing a significant increase in productivity. Sound Droid incorporates a large variety of special processing – including reverberation, pitch-changing, and Doppler shift. In addition, custom signal-processing software modules can be provided to suit the particular needs of the user. A sophisticated data-base management system facilitates tracking the flow of sound through a production. Sound Droid is based on the audio signal processor, a programmable digital signal processor. A modular architecture makes it possible to adjust the system configuration to suit the needs of the user. Later developments will be based on the same signal-processing hardware, changing only the software and user interface. For example, systems could be provided with additional sliders in a mixing system, multiple operator consoles for a large-scale post-production, and even a keyboard for sound synthesis.