Festival Speech Synthesis System (1997)

Introduction

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Historical Context

Before Voder, several significant milestones have marked progress in recreating human speech artificially.

The earliest attempts towards speech synthesis using mechanical means can be traced back to 1779 when Christian Gottlieb Kratzenstein produced the five vowel sounds /a/, /e/, /i/, /o/, /u/ using various shaped tubes. A few years later, W. R. von Kempelen of Vienna further advanced this and managed to produce not only vowel sounds but also a number of consonant sounds. His Speaking Machine, dating back to the late 18th century, utilized bellows and reeds to simulate limited vowel and consonant sounds, underscoring the potential for creating full-fledged artificial speech.

Charles Wheatstone built upon Kempelen's work with his Speaking Machine in the early 19th century. By incorporating a vibrating reed, Wheatstone's machine could produce a wider range of sounds compared to previous attempts, resulting in more accurate and recognizable speech sounds.

Working Mechanism

The Voder is a manually operated speech synthesizer that recreates the physiological characteristics of the human voice. It works by breaking up human speech into its acoustic components using a set of ten contiguous band-pass filters that cover the entire speech frequency range and are connected in parallel. The pass bands of the filters were chosen after a careful analysis of how the human ear interprets speech sounds. The initial sounds produced by either the oscillator or the gas discharge tube were passed through these filters, and their outputs were passed through an amplifier that mixed and modulated them and passed it on to a loudspeaker in order to produce an electronic human speech. The potentiometers (devices that control how much electricity flows through a circuit) controlled by the finger keys were used to operate the band-pass filter outputs.

Two basic sounds are used to create speech sounds: the buzz tone and the hissing noise. The buzz tone is used to create voiced vowels and nasal sounds, while the hissing noise is used to create voiceless fricative sounds. The pitch control is achieved by a foot pedal, which also converts the tones and hissing sounds to vowels, consonants, and inflections. The Voder's filters divide speech sounds into their acoustic components, which are then recreated using the buzz and hiss sounds.

Key Innovations

The Voder was among the first devices to allow manual control of speech synthesis. It was a pioneer in electronic sound generation, breaking down human speech into its fundamental acoustic components and reproducing these patterns electronically: this was a significant advancement in the early stages of electronic speech synthesis. Moreover, Voder was the first successful attempt at recreating an important physiological characteristic of the human voice – the ability to create voiced and unvoiced sounds.

To improve the operator's performance, the Voder had a recording and playback feature that allowed operators to objectively analyze their areas of improvement. This feature is similar to modern-day contact centers that use call recording and analysis to improve agent performance.

Impact

The Voder was demonstrated to the public at the 1939 New York World's Fair, attracting widespread attention and showcasing the possibilities of artificial speech production. It was a significant step towards public awareness and interest in the field of speech synthesis.

In fact, the abilities of Voder go beyond human voice, as it can also produce non-speech sounds such as musical tones and sound effects, and thus it was used in a variety of applications, including radio broadcasts, sound effects for movies, and even music performances.

Future research

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Team Members

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