Method for controlling duration in speech synthesis

1. A method of synthesizing of a speech signal using processing apparatus, comprising:

the processing apparatus automatically assigning of a first identifier to a first class of steady intervals of an original speech signal and assigning of a second identifier to a second class of dynamic intervals of the original speech signal,

the processing apparatus automatically windowing the original speech signal to provide a number of pitch bells,

the processing apparatus automatically processing the pitch bells having the first identifier assigned thereto for modifying a duration of the speech signal, and

the processing apparatus automatically performing an overlap and add operation on the processed pitch bells

the processing apparatus outputting the overlapped and added pitch bells as a synthesized speech signal.

2. The method of claim 1 , wherein the first identifier is selected between a first code and a second code, the first code being indicative of an unvoiced interval and the second code being indicative of a voiced interval.

3. The method of claim 1 , whereby the second identifier is selected between a third code, a fourth code, a fifth code and a sixth code, the third code being indicative of an unvoiced interval being essential for the intelligibility of the speech signal, the fourth code being indicative of a voiced interval being essential for the intelligibility of the speech signal, and the fifth code being indicative of an unvoiced interval not being essential for the intelligibility of the speech signal and the sixth code being indicative of a voiced interval not being essential for the intelligibility of the speech signal.

4. The method of claim 3 wherein pitch bells being assigned to the fifth or sixth code are at some times deleted and at other times not deleted.

5. The speech signal of claim 1 wherein one or more pitch bells belonging to a dynamic voice or unvoiced interval have been deleted prior to the overlap and add operation.

6. The method of claim 1 wherein a raised cosine is used for windowing of the speech signal.

7. The method of claim 1 , wherein a sine window is used for windowing of steady, unvoiced intervals of the speech signal.

8. The methods of claim 1 , comprising randomizing the pitch bells of steady, unvoiced periods before performing the overlap and add operation.

9. The method of claim 1 , wherein the windowing is performed by means of a logical window positioned synchronously with a fundamental frequency of the speech signal.

10. A synthesized speech signal output by the method of claim 1 , and embodied as physical variations of properties of a computer detectable media.

11. A text-to-speech computer system, comprising:

means for storing of a speech signal,

means for storing of first identifiers being assigned to a first class of steady intervals of an original speech signal and for storing of a second identifiers being assigned to a second class of dynamic intervals of the original speech signal,

means for logically windowing the speech signal to provide a number of pitch bells,

means for processing the pitch bells having the first identifier assigned thereto for modifying a duration of the speech signal,

means for performing an overlap and add operation on the processed pitch bells,

means for outputting the overlapped and added pitch bells as a synthesized speech signal.

12. The speech signal of claim 11 wherein one or more pitch bells belonging to a dynamic voice or unvoiced interval have been deleted prior to the overlap and add operation.

13. A synthesized speech signal output by the text-to-speech system of claim 11 , and embodied as physical variations of properties of a computer detectable media.

14. The synthesized speech signal of claim 13 wherein the media is a computer memory in which the synthesized speech signal is stored.