Speech synthesis

• US 20040172249A1
• Filed: 04/19/2004
• Published: 09/02/2004
• Est. Priority Date: 05/25/2001
• Status: Abandoned Application

• Current Assignee: Rhetorical Group Plc (The Registrant)
• Original Assignee: Rhetorical Group Plc (The Registrant)
• Inventors: Aylett, Matthew Peter, Fackrell, Justin Wynford Andrew, Taylor, Paul Alexander
• Application Number:
  US10/478,348
• Publication Number:
  US 20040172249A1
• Time in Patent Office: Days
• US Class Current: 704/260
• CPC Class Codes: G10L 13/04 Details of speech synthesis systems, e.g. synthesiser structure or memory management
• CPC Class Codes: G10L 13/07 Concatenation rules

Abstract

The invention makes use of a database of diphones derived from natural speech. A text is rendered as a series of target diphones and for each of these a number of predetermined diphone features are identified. Potential matches from the database are identified and a target cost for each of these features is established. The target costs are modified before selecting a least-cost combination. The modification of the target costs may be done by weighting, or by use of distribution functions. The calculation of the least-cost combination may be performed by a dynamic search program such as a Viterbi search. In the preferred embodiments, diphone join costs are also included in the least-cost calculation, and are also modified before the calculation is made. In addition to, or instead of, modification of target costs, the potential matches may be pre-pruned to identify a predetermined number of potential matches in descending order of suitability.

Claims

1. A method of producing synthesised speech from a text, comprising:

(a) providing a database of diphones derived from samples of natural speech;

(b) analysing the text to render the text as a succession of target diphones;

(c) identifying, for each target diphone, the value of each of a number of predetermined diphone features;

(d) identifying in the database diphones which are potential matches to each target diphone;

(e) establishing a target cost for each of said predetermined features of each potential database diphone in relation to each target diphone;

(f) modifying the target cost of each feature in accordance with predetermined factors associated with said diphone features; and

(g) calculating the least-cost combination to achieve output speech corresponding to the text.

2. A method according to claim 1, including evaluating the join cost of joining each diphone to its successor, and including the join costs in the least-cost calculation.

3. A method according to claim 2, in which the join costs are also modified in accordance with predetermined features of one or both of the target diphone and candidate diphone.

4. A method according to claim 3, in which the modification of diphone feature costs and join costs is effected using a simple weighting procedure.

5. A method according to claim 3, in which the modification of diphone feature costs and join costs makes use of distribution functions.

6. A method according to claim 5, in which the cost is modified according to a cost function which is V-shaped, and the zero-cost point is located using the centroid of a pre-established probability distribution.

7. A method according to claim 6, in which the slope of the V is modified in dependence on the variance of the probability distribution.

8. A method according to claim 5, in which the cost is modified according to a cost function which is the inverse of a pre-established probability distribution.

9. A method according to any preceding claim, in which calculation of the least-cost combination is performed by a dynamic search program.

10. A method according to claim 9, in which the dynamic search program is a Viterbi search.

11. A method according to any preceding claim and including the step of pre-pruning candidate diphones on the basis of categorical features.

12. A method according to claim 11, in which the pre-pruning step makes use of a decision tree working on predetermined categorical features of the candidate diphones.

13. A method according to claim 12, in which said diphone features are one or more of phonetic, prosodic, linguistic, and acoustic features.

14. A method according to claim 13, in which said features are one or more of:

word

syllable

adjacent word pair

stress

duration

pitch

intonation contour

position in sentence

text type

text subject matter

15. A method according to any of claims 11 to 14, in which the pre-pruning step assigns values based on suitability to the target diphones, and in which said pre-pruning values are used in assigning target costs.

16. A method of producing synthesised speech from a text, comprising:

(a) providing a database of diphones derived from samples of natural speech;

(b) analysing the text to render the text as a succession of target diphones;

(c) identifying, for each target diphone, the value of each of a number of predetermined diphone features;

(d) identifying in the database diphones which are potential matches to each target diphone;

(e) pre-pruning said potential matches by means of sorting by category to identify a predetermined number of potential matches of descending order of suitability;

(f) establishing a target cost for each of said predetermined features of each potential database diphone in relation to each target diphone; and

(g) calculating the least-cost combination to achieve output speech corresponding to the text.

17. A method according to claim 16, in which said pre-pruning is effected by means of a decision tree.

18. A method according to claim 16 or claim 17, in which said pre-pruning step assigns values based on suitability to the target diphones, and in which said pre-pruning values are used in assigning target costs.

19. A system for producing synthesised speech from text, the system comprising:

memory means storing a database of diphones derived from natural speech;

processing means arranged to;

(a) analyse the text to render the text as a succession of target diphones;

(b) identify, for each target diphone, the value of each of a number of predetermined diphone features;

(c) identify in the database diphones which are potential matches to each target diphone;

(d) establish a target cost for each of said predetermined features of each potential database diphone in relation to each target diphone;

(e) modify the target cost of each feature in accordance with predetermined factors associated with said diphone features; and

(f) calculate the least-cost combination to achieve output speech corresponding to the text; and

speech synthesis means operable to retrieve and concatenate the diphones identified as constituting said least cost combination.

21. A data carrier holding software adapted to cause a processing means to operate steps (a)-(f) of claim 19 or claim 20.

20. A system for producing synthesised speech from text, the system comprising:

memory means storing a database of diphones derived from natural speech;

processing means arranged to;

(a) analyse the text to render the text as a succession of target diphones;

(b) identify, for each target diphone, the value of each of a number of predetermined diphone features;

(c) identify in the database diphones which are potential matches to each target diphone;

(d) pre-prune said potential matches by means of sorting by category to identify a predetermined number of potential matches of descending order of suitability;

(e) establish a target cost for each of said predetermined features of each potential database diphone in relation to each target diphone; and

(f) calculate the least-cost combination to achieve output speech corresponding to the text; and

speech synthesis means operable to retrieve and concatenate the diphones identified as constituting said least cost combination.