Speaker recognition generally includes the tasks of speaker identification and speaker verification: speaker identification involves labeling an unknown voice as one from a set of known voices, while speaker verification involves determining whether an unknown voice matches the known voice of a speaker whose identity is being claimed. In particular, speaker identity verification based on a person's voice is of considerable interest for providing telephone access to such services as banking transactions, credit card verification, remote access to dial-up computer databases.
The specific problem for which the invention has application is providing verified access to medical records databases for health care providers. For example, a voice log-in system would be used by doctors to obtain verified access to a number of medical databases at different health care institutions.
Two approaches to voice verification technology have been used: voice/mechanical and total voice. In a voice/mechanical system, a user manually enters a digit code and then speaks a voice password--the voice password is compared with a reference acoustic recognition model retrieved based on the secret code. In a total voice system, a user speaks a digit code--speaker-independent digit recognition is used to recognize the digits, and then a reference acoustic recognition model is loaded based on the recognized digit string, and voice verification is performed.
The total voice system can be described as a template-based, fixed-text speaker verification task. It includes the subtasks: (a) enrollment--creating a reference template composed of a set of speech features, as a function of time, associated with the fixed-text digit code for each valid user; (b) verification--selecting an appropriate reference template based on speaker-independent recognition of the digit code, and comparing input speech with reference templates at equivalent points in time, with a decision being based on similarity between input and reference, integrated over time; and (c) reference update--adapting the reference templates to accommodate changes in a valid user's speech after successful verification.
The enrollment procedure builds an initial reference template for a speaker by capturing the digit code, typically by examining the speech energy profile and determining the end points in time. For each successful verification, the dynamic reference updating procedure averages the feature sets associated with the reference template and the input speech, and the reference template is updated accordingly, thereby accommodating changes in a persons speech input as familiarity with the system is achieved.
Both the voice/mechanical and the total voice speaker verification systems are disadvantageous in that each requires the use of a specific digit code (either entered or spoken). In the medical records database application, such a requirement is problematic to the point of impracticality. Doctors and other health care providers typically see patients at a number of hospitals, each of which has its own medical records database system. These systems typically assign each user a unique identification code, requiring each health care provider to remember a different identification code for each institution and database system.
Accordingly, a need exists for a speaker verification system that is not based on the spoken input of an identification code.