Speech Interfaces: Session Introduction

SPEECH IbrrERFACES: SESSION IN~ODUCTION Douglas L. Hogan 13625 Middlevale Lane Silver Spring, ~m 20906 ABSTRACT II CURRENT TECHNOLOGY The speech interface is the natural one for the human user and is beginning to be used in a limited way in many applications. Some of these applications are experimental; still others have achieved the status of cost-effective utility. A brief summary of the current state-of-the-art of speech input and output are presented. The two papers in the session represent specific examples of current work. Some comments on the need for linguistically oriented development conclude the paper. I INTRODUCTION Over the past four decades it has often been felt that the solution to the problem of "machine recognition of speech" is ".. just around the corner." When the sound spectrograph was invented (a little less than forty years ago) engineers, acousticians, phoneticists, and linguists were certain that the mysteries of speech were about to be unveiled. When powerful computers could be brought to bear (say - twenty years ago) there was a renewed feeling that such tools would provide the ~eans to a near term solution. When artifi- cial intelligence was the buzzword (a little over ten years ago) it was clear that now the solution of the recognition problem was at hand. Where are we today? A number of modest, and modestly priced, speech recognition systems are on the market and in use. This has come about because technology has permitted some brute force methods to be used and because simple applications have been found to be cost effective. In speech output systems a similar pattern has emerged. Crude synthesizers such as the ~askins pattern playback of thirty years ago were capable of evoking "correct" responses from lis- teners. Twenty-five years ago it was thought that reading machines for the blind could be construc- ted by concatenating words. Twenty years ago formant synthesizers sounded extremely natural when their control was a "copy" of a natural utterance. Modern synthesizers are one one-thou- sandth the size and cost; they still only sound natural when a human utterance is analyzed and then resynthesized as a complete entity. Conca- tenatin 8 words is still no better, though cheaper, than it was twenty years ago. A. Speech Input There are now several speech recognition systems on the market which are intended to recog- nize isolated words and which have been trained for an individual speaker. The vocabulary sizes are on the order of 100 words are phrases. Accu- racy is always quoted at "99+%." These recogni- zers use a form of template matching within a space which has the dimensions of features versus time. The "true" accuracy is a function of the vocabulary size, the degree of cooperativeness of the speaker, and the innate dissimilarity of the vncab ulary. Since the systems are recognizing known words by known speakers the major source of varia billty in successive words is the time axis. The same word may (and will) be spoken at differ- ent speaking rates. Unfortunately, …

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