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15.4 Key Component — Text To Speech (TTS)

Emacspeak is a speech-subsystem for Emacs; it depends on an external Text-To-Speech (TTS) engine to produce speech. In 1994, Digital Equipment released what would turn out to be the last in the line of hardware DECTalk synthesizers, the DECTalk Express. This was essentially an Intel 386with 1mb of flash memory that ran a version of the DECTalk TTS software — to date, it still remains my favorite Text-To-Speech engine. At the time, I also had a software version of the same engine running on my DEC-Alpha workstation; the desire to use either a software or hardware solution to produce speech output defined the Emacspeak speech-server architecture.

I went to IBM Research in 1999; this coincided with IBM releasing a version of the Eloquennce TTS engine on Linux under the name ViaVoice Outloud. My colleague Jeffrey Sorenson implemented an early version of the Emacspeak speech-server for this engine using the OSS API; I later updated it to use the ALSA library while on a flight back to SFO from Boston in 2001. That is still the TTS engine that is speaking as I type this article on my laptop.

20 years on, TTS continues to be the weakest link on Linux; the best available solution in terms of quality continues to be the Linux port of Eloquence TTS available from Voxin in Europe for a small price. Looking back across 20 years, the state of TTS on Linux in particular and across all platforms in general continues to be a disappointment; most of today’s newer TTS engines are geared toward mainstream use-cases where naturalness of the voice tends to supersede intelligibility at higher speech-rates. Ironically, modern TTS engines also give applications far less control over the generated output — as a case in point, I implemented Audio System For Technical Readings (AsTeR) in 1994 using the DECTalk; 20 years later, we implemented MathML support in ChromeVox using Google TTS. In 2013, it turned out to be difficult or impossible to implement the type of audio renderings that were possible with the admittedly less-natural sounding DECTalk!


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