Method and system of dynamically adjusting a speech output rate to match a speech input rate

[0001] 1. Technical Field

[0002] This invention relates to the field of speech reproduction, and more particularly to a method and system for matching the speed of speech output to a speech input in a speech application.

[0003] 2. Description of the Related Art

[0004] In current speech application systems, there is no way to dynamically adjust the rate of speech output to match a user's speech input rate. In a very high quality speech system, it would be desirable to dynamically match the rate of speech output to a user's speech input rate to make the system more comfortable and pleasant for the user. There are existing methods for adjusting speech output rates for both artificial and recorded speech, but none of these methods include the ability to match and dynamically adjust to a speech input rate.

[0005] An example of such static adjustment is illustrated in U.S. Pat. No. 6,490,553 entitled “Apparatus and method for controlling rate of playback of audio data” which discusses a method and apparatus that controls the rate of playback of audio data corresponding to a stream of speech. Using speech recognition, the rate of speech of the audio data is determined. The determined rate of speech is compared to a target rate. Based on the comparison, the playback rate is adjusted, i.e. increased or decreased, to match the target rate. Although this reference adjusts the playback rate, it is for use in the field of closed captioning video and only teaches the use of rates derived from speech recognition of the audio portion of the video to match the audio output rate to a predefined non-dynamic or fixed target rate. It fails to describe a method for dynamically and automatically matching the speed of speech output (including TTS output) to speech input in a speech application.

[0006] Embodiments in accordance with the invention can enable a method and system for dynamically and automatically adjusting a speech output rate by determining the speech input rate and matching the speech output rate to match the speech input rate. The speech input rate can be determined using a running average of the rates computed for the last n utterances. This estimate of the speech input rate can be fed back into a speech production mechanism to adjust the speech output rate to match the speech input rate for either text-to-speech (TTS) or recorded speech output.

[0007] In a first aspect of the invention, a method of dynamically and automatically adjusting a speech output rate to match an speech input rate can include the steps of receiving a speech input, computing a speech input rate from the speech input, and dynamically adjusting the speech output rate to match the speech input rate. The step of computing the speech input rate can include the step of computing a running average of the rates computed for the last n utterances of the speech input. The method can further include the step of feeding back an estimate of the speech input rate to a speech production mechanism to adjust the speech output rate. The method can further include the step of determining a type of speech output. If the type of speech output is text-to-speech (TTS), then the method can further include the step of adjusting a rate of text-to-speech synthesis to match the speech input rate if the type of speech output is text-to-speech. If the type of speech output is recorded and alternate text is available, then the method can further include the step of counting alternate text available from a recorded output and determining an audio file length to compute a default output rate which is used to adjust a recorded output rate to match the input speech rate. Alternatively, if the type of speech is recorded and alternate text is unavailable, then the method can include the steps of obtaining an output word count from a transcription of a recorded speech output and determining an audio file length to compute a default output rate which is used to adjust a recorded output rate to match the input speech rate.

[0008] In a second aspect of the invention, a system for dynamically and automatically adjusting an speech output rate to match an speech input rate can include a memory and a processor. The processor can be programmed to receive a speech input, compute a speech input rate from the speech input, and dynamically adjust the speech output rate to match the speech input rate. The processor can be further programmed to determine a type of speech output. The processor can be programmed to adjust a rate of text-to-speech synthesis to match the speech input rate if the type of speech output is text-to-speech. The processor can also be programmed to count alternate text available from a recorded output and determine an audio file length to compute a default output rate which is used to adjust a recorded output rate to match the input speech rate when the type of speech is recorded and alternate text is available. The processor can also be programmed to obtain an output word count from a transcription of a recorded speech output and determine an audio file length to compute a default output rate which is used to adjust a recorded output rate to match the input speech rate when the type of speech is recorded and alternate text is unavailable.

[0009] In a third aspect of the invention, a computer program has a plurality of code sections executable by a machine for causing the machine to perform certain steps as described in the method and systems outlined in the first and second aspects above.

[0012] Embodiments in accordance with the invention can determine a user's speech input rate and use such information to dynamically and automatically adjust the speech output rate. Referring to FIG. 1, a high-level flowchart of a method 10 having a plurality of callflow elements or steps in accordance with the present invention is shown.

[0013] The method 10 begins by waiting for speech input at step 12 and computing the speech input rate at step 14. The output of any speech recognition step can be the production of a text string. As a background process, the text string along with information about the amount of time required to produce the text string can be used to compute a speech input rate in words per minute for example. As an enhancement to ensure stability of estimated input rates, a running average of the rates computed for the last n utterances can be used as the measure of a speech input rate. This estimate of speech input rate can then be fed back (as shown after an adjustment step 18) into the speech production mechanism to adjust the speech output rate. This is fairly easy for speech generated via a text-to-speech engine, but is a little more complicated for recorded speech. Thus, once the speech input rate is determined, the type of speech output should be determined at step 16. If the speech input is TTS, the TTS output rate can be adjusted to match the input rate at step 18.

[0014] If the output speech is recorded at step 16, then the number of words in the output can be determined by two different methods. If the code for the output speech includes the output text (for example, alt text included as part of an <audio> tag in VOICEXML™) at step 20, then it's easy to determine the number of words in the segment by using the alternate text to get an output word count at step 22. Using the word count and an audio file length, a default output rate can be determined at step 24. If there is no alternate text available for the recorded segment at step 20, then the segment could be decoded by a transcription server (or similar program) to estimate the number of words in the segment at step 21. After determining (or estimating) the number of words in the recorded segment, the speech output rate can be computed by dividing the number of words in the text by the length of the recorded segment (which is a property of the audio file) at step 24. After computing the default output rate, the recorded output rate can be adjusted to match the input rate at step 26. Using known technologies (for example, PSOLA), it is possible to change the speed of production of recorded speech without changing the fundamental frequency of the voice.

[0015] It should be understood that the present invention can be realized in hardware, software, or a combination of hardware and software. The present invention can also be realized in a centralized fashion in one computer system, or in a distributed fashion where different elements are spread across several interconnected computer systems. Any kind of computer system or other apparatus adapted for carrying out the methods described herein is suited. A typical combination of hardware and software can be a general purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the methods described herein.

[0016] The present invention also can be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which when loaded in a computer system is able to carry out these methods. Computer program or application in the present context means any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following: a) conversion to another language, code or notation; b) reproduction in a different material form.

[0017] This invention can be embodied in other forms without departing from the spirit or essential attributes thereof. Accordingly, reference should be made to the following claims, rather than to the foregoing specification, as indicating the scope of the invention.