a preferred embodiment of the present invention will now be described in detail in accordance with the accompanying drawings . [ 0026 ] fig1 is a block diagram showing the hardware arrangement of a speech synthesizing apparatus according to this embodiment . referring to fig1 reference numeral 11 denotes a central processing unit for performing processing such as numeric operation and control , which realizes control to be described later with reference to the flow chart of fig2 ; 12 , a storage device including a ram , rom , and the like , in which a control program required to make the central processing unit 11 realize the control described later with reference to the flow chart of fig2 and temporary data are stored ; and 13 , an external storage device such as a disk device storing a control program for controlling speech synthesis processing in this embodiment and a control program for controlling a graphical user interface for receiving operation by a user . reference numeral 14 denotes an output device formed by a speaker and the like , from which synthesized speech is output . the graphical user interface for receiving operation by the user is displayed on a display device . this graphical user interface is controlled by the central processing unit 11 . note that the present invention can also be incorporated in another apparatus or program to output synthesized speech . in this case , an output is an input for this apparatus or program . reference numeral 15 denotes an input device such as a keyboard , which converts user operation into a predetermined control command and supplies it to the central processing unit 11 . the central processing unit 11 designates a text ( in japanese or another language ) as speech synthesis target , and supplies it to a speech synthesizing unit 17 . note that the present invention can also be incorporated as part of another apparatus or program . in this case , input operation is indirectly performed through another apparatus or program . reference numeral 16 denotes an internal bus , which connects the above components shown in fig1 ; and 17 , a speech synthesizing unit for synthesizing speech from an input text by using a speech segment dictionary 18 . note that the speech segment dictionary 18 may be stored in the external storage device 13 . an embodiment of the present invention will be described below in consideration of the above hardware arrangement . fig2 is a flow chart showing a procedure for processing in the speech synthesizing unit 17 . a speech synthesizing method according to this embodiment will be described below with reference to this flow chart . in step s 1 , language analysis and acoustic processing are performed for an input text to generate a phoneme series representing the text and prosody information of the phoneme series . in this case , the prosody information includes a duration length , fundamental frequency , and the like . a prosody unit is a diphone , phoneme , syllable , or the like . in step s 2 , speech waveform data representing a speech segment as one prosody unit is read out from the speech segment dictionary 18 on the basis of the generated phoneme series . fig3 is a view showing an example of the speech waveform data read out in step s 2 . in step s 3 , the pitch synchronization positions of the speech waveform data acquired in step s 2 and the corresponding window functions are read out from the speech segment dictionary 18 . fig4 a is a view showing a speech waveform . fig4 b is a view showing a plurality of window functions corresponding to the pitch synchronization positions of the speech waveform . the flow then advances to step s 4 to extract the speech waveform data loaded in step s 2 by using the plurality of window functions loaded in step s 3 , thereby obtaining a plurality of small speech segments . fig5 a shows a speech waveform . fig5 b shows a plurality of window functions corresponding to the pitch synchronization positions of the speech waveform . fig5 c shows the plurality of small speech segments obtained by using the window functions in fig5 b . in the following processing in steps s 5 to s 10 , limitations on waveform editing operation for each small speech segment are checked by using the speech segment dictionary 18 . in this embodiment , in the speech segment dictionary 18 , editing limitation information ( information of limitations on waveform editing operation ) is added to a window function corresponding to each small speech segment on which a waveform editing operation limitation such as deletion , repetition , and interval change is imposed . the speech synthesizing unit 17 therefore checks editing limitation information for a given small speech segment by discriminating a specific ordinal number of a window function by which the small speech segment is extracted . in this embodiment , as editing limitation information , a speech segment dictionary is used , which stores , as editing limitation information , deletion inhibition information indicating a small speech segment which should not be deleted , repetition inhibition information representing a small speech segment which should not be repeated , and internal change inhibition information representing a small speech segment for which an interval change is inhibited . the following are examples of the editing limitation information registered in the speech segment dictionary : ( 1 ) “ voiced / unvoiced boundary ”: since “ voiced / unvoiced boundary ” is information to be used in another process in speech synthesis , it is stored as “ voiced / unvoiced boundary information ” in the speech segment dictionary . the rule that “ repetition / deletion inhibition ” should be added for a voiced / unvoiced boundary is applied to a program during execution . note that voiced / unvoiced boundary information is registered in the dictionary after it is automatically detected without any modification by the user . ( 2 ) “ plosive ”: if a small speech segment is a plosive , the editing limitation information of “ repetition / deletion inhibition ” is registered in the speech segment dictionary . note that a small speech segment at the time point of plosion is manually designated , and editing limitation information is added to it . ( 3 ) “ spectrum change amount ”: a small speech segment exhibiting a large spectrum change amount is automatically discriminated , and editing limitation information is added to it . in this embodiment , “ repetition / deletion inhibition ” is added to a small speech segment exhibiting a large spectrum change amount . note that a person determines what editing limitation is appropriate for a certain phenomenon ( plosion or the like ), and makes a rule based on the determination , thereby registering the corresponding information in the dictionary . in step s 5 , editing limitation information added to each window function is checked to obtain a window function to which deletion inhibition information is added . in step s 6 , a marking that indicates deletion inhibition with respect to a small speech segment corresponding to the window function is made . fig6 a to 6 c show how the marking of “ deletion inhibition ” is made on a small speech segment . the speech segment dictionary 18 in this embodiment stores deletion inhibition information for a window function corresponding to an unsteady portion of a speech segment ( especially , a portion near the boundary between a voiced sound portion and an unvoiced sound portion at which the shape of a waveform greatly changes ). referring to fig6 a to 6 c , the marking of “ deletion inhibition ” is made on the small speech segment obtained by the third window function ( corresponding to the boundary between the voiced sound portion and the unvoiced sound portion ). in the speech segment dictionary 18 in this embodiment , “ deletion inhibition ” is added to the third window function , and the marking of deletion inhibition is made as shown in fig6 c . likewise , in step s 7 , editing limitation information added to each window function is checked to obtain a window function to which repetition inhibition information is added . in step s 8 , a marking that indicates repetition inhibition is made with respect to a small speech segment corresponding to the window function obtained in step s 7 . fig7 a to 7 c are views showing how the marking of “ repetition inhibition information ” is made on a predetermined small speech segment . the speech segment dictionary 18 in this embodiment stores repetition inhibition information for a window function corresponding to an unsteady portion of a speech segment ( especially , a portion near the boundary between a voiced sound portion and an unvoiced sound portion at which the shape of a waveform greatly changes ). referring to fig7 a to 7 c , the marking of “ repetition inhibition information ” is made on the small speech segment obtained by the fourth window function ( corresponding to the head portion of the voiced sound portion ). in the speech segment dictionary 18 in this embodiment , “ repetition inhibition information ” is added to the fourth window function , and the marking is made as shown in fig7 c . note that the marking of “ deletion inhibition ” indicates the marking made in step s 6 ( see fig6 a to 6 c ). in step s 9 , the editing limitation information added to each window function is checked to obtain a window function to which interval change inhibition information is added . in step s 10 , a marking that indicates interval change inhibition is made with respect to a small speech segment corresponding to the window function obtained in step s 9 . fig8 a to 8 c are views showing how the marking of “ interval change inhibition information ” is made on a predetermined small speech segment . the speech segment dictionary 18 in this embodiment stores interval change inhibition information for a window function corresponding to an unsteady portion of a speech segment ( especially , a portion near the boundary between a voiced sound portion and an unvoiced sound portion at which the shape of a waveform greatly changes ). referring to fig8 a to 8 c , the marking of “ interval change inhibition information ” is made on the small speech segment obtained by the third window function ( corresponding to the boundary between the voiced sound portion and the unvoiced sound portion ). in the speech segment dictionary 18 in this embodiment , “ interval change inhibition information ” is added to the third window function , and the marking is made as shown in fig8 c . note that the markings of “ deletion inhibition ” and “ repetition inhibition information ” indicate the markings made in steps s 6 and s 8 ( see fig6 a to 6 c and 7 a to 7 c ). in step s 11 , the small speech segments extracted in step s 4 are arranged and overlapped again to match the prosody information obtained in step s 1 , thereby completing editing operation for one speech segment . when the duration length is to be decreased , a small speech segment on the marking of “ deletion inhibition ” does not become a deletion target . when the duration length is to be increased , a small speech segment on which the marking of “ repetition inhibition ” is made does not become a repetition target . when the fundamental frequency is to be changed , a small speech segment on which the marking of “ interval change inhibition ” does not become an interval change target . the above waveform editing operation is then performed for all the speech segments constituting the phoneme series obtained in step s 1 , and synthesized speech corresponding to the input text is obtained by concatenating the respective speech segments . this synthesized speech is output from the speaker of the output device 14 . in step s 11 , the waveform of each speech segment is edited by using the psola ( pitch - synchronous overlap add ) method . as described above , according to the above embodiment , by setting waveform editing operation permission / inhibition information about deletion , repetition , interval change , and the like for each small speech segment obtained from a speech segment as one prosody unit , waveform editing operation limitations can be imposed on unsteady portions of each speech segment ( especially , a portion near the boundary between a voiced sound portion and an unvoiced sound portion at which the shape of a waveform greatly changes ). this makes it possible to suppress the occurrence of rounded speech waveforms and strange sounds due to changes in duration length and fundamental frequency , thus obtaining more natural synthesized speech . in the above embodiment , the positions of window functions are used for deletion inhibition information , repetition inhibition information , and interval change inhibition information . however , they may be acquired as indirect information . more specifically , boundary information such as a phoneme boundary or voice / unvoiced boundary is acquired , and the marking of deletion inhibition , repetition inhibition , and interval change inhibition may be made on a small speech segment located at the boundary . in the above embodiment , deletion inhibition information , repetition inhibition information , and interval change inhibition information may not be information indicating a small speech segment but may be information indicating a specific interval . more specifically , information at the time point of plosion may be acquired from a plosive , and the marking of deletion inhibition , repetition inhibition , or interval change inhibition may be made on a small speech segment present in intervals before and after the time point of plosion . the present invention may be applied to a system constituted by a plurality of devices ( e . g ., a host computer , an interface device , a reader , a printer , and the like ) or an apparatus comprising a single device ( e . g ., a copying machine , a facsimile apparatus , or the like ). the present invention can also be applied to a case wherein a storage medium storing software program codes for realizing the functions of the above - described embodiment is supplied to a system or apparatus , and the computer ( or a cpu or an mpu ) of the system or apparatus reads out and executes the program codes stored in the storage medium . in this case , the program codes read out from the storage medium realize the functions of the above - described embodiment by themselves , and the storage medium storing the program codes constitutes the present invention . the functions of the above - described embodiment are realized not only when the readout program codes are executed by the computer but also when the os ( operating system ) running on the computer performs part or all of actual processing on the basis of the instructions of the program codes . the functions of the above - described embodiment are also realized when the program codes read out from the storage medium are written in the memory of a function expansion board inserted into the computer or a function expansion unit connected to the computer , and the cpu of the function expansion board or function expansion unit performs part or all of actual processing on the basis of the instructions of the program codes . as has been described above , according to the present invention , processing for prosody control can be selectively limited with respect to small speech segments in each speech segment , thereby preventing a deterioration in synthesized speech due to waveform editing operation . as many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof , it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the claims .