Draft:Computalker CT-1 Speech Synthesizer

Computalker CT-1 Speech Synthesizer

The COMPUTALKER Model CT-1 Speech Synthesizer was an analog speech synthesizer unit designed for the standard S-100 bus. Developed to work with 8080 and Z-80 microcomputers, the CT-1 synthesized speech by utilizing acoustic-phonetic parameters which dictated the fundamental aspects of speech perception. These parameters were transmitted to the synthesizer through the S-100 data bus, allowing real-time speech production under software control. The device was capable of transmitting data at rates between 500 and 900 bytes per second.

Hardware Implementation

The CT-1 was an analog synthesizer that consisted of seven modules that implemented a model of the human vocal tract. Inputs included a variable frequency oscillator or “pulse source” and a noise generator. The outputs of these sources were combined and fed to three branches: 1) a resonator for the nasal branch, 2) three sequential resonators in the oral branch, and 3) a resonator for the frictation branch. There were a total of nine inputs to this model in the form of 8-bit DACs (digital to analog converters) that allowed for control of the amplitude and frequency of the pulse source, the resonators and amplifiers. The oscillator controlled the voice pitch. Tunable single pole bandpass resonators determined the frequency or spectral shape of the speech output in various ways. The data rate to achieve high quality speech for these parameters was less than 100 updates per second.

Operational Modes

The CT-1 featured two main operational modes:

1. Direct Parameter Control Mode: This mode used previously decoded words to recreate speech, preserving the original speaker's mannerisms and nuances, but with a limited vocabulary.
2. Phonetic Mode: This phoneme-based mode smoothed phoneme parameters into parabolic trajectories, resulting in more fluid and less mechanical-sounding speech.

Pricing and Availability

At its launch in 1977, the CT-1 was priced between $425 and $550, depending on the software options included. Versions pre-packaged for the Apple II and TRS-80 were also available, costing around $595. Approximately 1000 units were sold between 1977 and 1981.

Historical Background

The CT-1 synthesizer was conceptualized and developed by the collaborative efforts of Jim Cooper and D. Lloyd Rice in Los Angeles. Their partnership began through a shared interest in electronic design and a specific focus on the synthesis of human speech and musical sounds.