Speech Technology Overview

• Many large companies have started adding speech recognition to their IVR systems. Just by phoning a number and speaking users can, for example, buy and sell stocks from Charles Schwab, check flight information with United Airlines, or order goods from Office Depot. The systems respond using a combination of pre-recorded prompts and an artificially generated voice.
• Microsoft Office XP users in the United States, Japan, and China can dictate text to Microsoft Word or PowerPoint® documents. Users can also use issue commands and control menus by speaking. For many users, particularly in Japan and China, dictating is far quicker and easier than using a keyboard. Office XP will speak back too. Excel, for example, reads back text as the user enters it into cells. This saves users from checking back and forth from screen to paper.

• Speech Recognition: Overview
• Speech Recognition: Potential Applications
• Speech Synthesis: Overview
• Speech Synthesis: Potential Applications

Speech Recognition

Speech recognition, or speech-to-text, involves capturing and digitizing the sound waves, converting them to basic language units or phonemes, constructing words from phonemes, and contextually analyzing the words to ensure correct spelling for words that sound alike (such as write and right). The figure below illustrates this high-level description of the process.


Figure 1 - Speech recognition process flow


Recognizers-also referred to as speech recognition engines- are the software drivers that convert the acoustical signal to a digital signal and deliver recognized speech as text to your application. Most recognizers support continuous speech, meaning you can speak naturally into a microphone at the speed of most conversations. Isolated or discrete speech recognizers require the user to pause after each word, and are currently being replaced by continuous speech engines.

Continuous speech recognition engines currently support two modes of speech recognition:

• Dictation, in which the user enters data by reading directly to the computer.
• Command and control, in which the user initiates actions by speaking commands or asking questions.

• Hands-free computing as an alternative to the keyboard, or to allow the application to be used in environments where a keyboard is impractical (e.g., small mobile devices, AutoPCs, or in mobile phones).
• A more "human" computer, one users can talk to, may make educational and entertainment applications seem more friendly and realistic.
• Voice responses to message boxes and wizard screens can easily be designed into an application.
• Streamlined access to application controls and large lists enables a user to speak any one item from a list or any command from a potentially huge set of commands without having to navigate through several dialog boxes or cascading menus.
• Speech-activated macros let a user speak a natural word or phrase rather than use the keyboard or a command to activate a macro. For example, saying "Spell check the paragraph" is easier for most users to remember than the CTRL+F5 key combination.
• Situational dialogs are possible between the user and the computer in which the computer asks the user, "What do you want to do?" and branches according to the reply. For example, the user might reply, "I want to book a flight from New York to Boston." The computer analyzes the reply, clarifies any ambiguous words ("Did you say New York?"), and then asks for any information that the user did not supply, such as "What day and time do you want to leave?"

Potential Applications for Speech Recognition

Speech Synthesis

Speech Synthesis, or text-to-speech, is the process of converting text into spoken language. This involves breaking down the words into phonemes; analyzing for special handling of text such as numbers, currency amounts, inflection, and punctuation; and generating the digital audio for playback. There are additional functions that the synthesizer performs, but Figure 2 below illustrates this high-level description of the process.


Figure 2 - Text-to-speech process flow


Software drivers called synthesizers, or text-to-speech voices, perform speech synthesis, handling the complexity of converting text and generating spoken language. A text-to-speech voice generates sounds similar to those created by human vocal cords and applies various filters to simulate throat length, mouth cavity, lip shape, and tongue position. Although easy to understand, the voice produced by synthesis technology tends to sound less human than a voice reproduced by a digital recording.

Nevertheless, text-to-speech applications may be the better alternative in situations where a digital audio recording is inadequate or impractical. Generally, consider using text-to-speech when:

• Audio recordings are too large to store on disk or expensive to record.
• The application response requires short phrases.
• The application cannot predict what it will need to communicate or alternative responses vary too much to record and store all possibilities. For example, speaking the time is a good use for text-to-speech, because the effort and storage involved in concatenating all possible times is manageable.
• The user prefers or requires audible feedback or notification. For example, audible proofreading of text and numbers helps the user catch typing errors missed by visual proofreading.

Potential Applications for Speech Synthesis

• The concatenated word/phrase text-to-speech can always replace recorded sentences. An application designer can easily pass the desired sentence strings to the text-to-speech engine.
• The inevitably non-human quality of synthesized text-to-speech makes it ideal for character voices that are supposed to be robots or aliens.
• If the application cannot afford to have recordings of all the possible dialogs or if the dialogs cannot be recorded ahead of time, then text-to-speech is the only alternative.