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Issue #207 October 2007
Embedded Speech
Speech Synthesis for Small Applications
by Nicusor Birsan & Ionut Tarsa
Start | Embedding Speech | Speech Synthesis Techniques | Open-Source Project | System Building Blocks | Sound From Luminary Micro | First Big Porting Problem | Synthesizer | Translator | The LM3S811 Speaks | More Speech Applications | Sources & PDF
EMBEDDING SPEECH
A lot has been written about speech synthesis. There is a plethora of scientific papers, books, devices, and professional software at your disposal. For instance, in a 1999 Circuit Cellar article, Rodger Richey explained how to build a text-to-speech system with small Microchip Technology PIC microcontrollers (“Talking Back,” Circuit Cellar 110). More recently, the subject also appeared in Jeff Bachiochi’s articles about the Winbond Electronics WTS701 (“Next-Generation Text to Speech,” Circuit Cellar 158, 2003) and the Magnevation SpeakJet (“Speech Synthesis with SpeakJet,” Circuit Cellar 178, 2005).
Basically, there are two approaches to embedding speech: storing sounds with low bit rates using various algorithms (ADPCM, LPC-10, and CELP) and drawing an external dedicated chip on a schematic. In this article, we’ll offer a way to embed the control application and the speech feature in the same chip.
If you analyze dedicated chip performance, you’ll find that most low-cost chips don’t generate high-quality speech. For example, the Emic text-to-speech module, a WTS701-based board, is good at speaking numbers, but when it comes to announcing something, its performance drops.
On the other hand, the RC Systems DoubleTalk RC8650 and RC8660 are versatile voice and sound synthesizers. They integrate a sophisticated text-to-speech processor, audio recording and playback, musical and sinusoidal tone generators, a telephone dialer, and an ADC, all in easy-to-use chipsets. The downside is that the modules are expensive.
The aforementioned devices have something in common: their manufacturers support application development with boards and software programs (e.g., RC Studio from RC Systems and ChipTalk from www.speechchips.com). Thus, we set out to design portable firmware for small microcontrollers and a desktop software tool for development and application tuning.
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