Method and apparatus for coding successive pitch periods in speech signal

• US 20030004709A1
• Filed: 06/11/2001
• Published: 01/02/2003
• Est. Priority Date: 06/11/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Nokia Corporation
• Inventors: Ruoppila, Vesa T., Pietila, Samuli, Heikkinen, Ari
• Granted Patent: US 6,584,437 B2
• Time in Patent Office: Days
• US Class Current: 704/207
• CPC Class Codes: G10L 19/08 Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters

Abstract

A method and apparatus for coding successive pitch periods of a speech signal. Based on a priori knowledge of statistical properties of successive speech periods, a shaped lattice structure is designed to cover the most probable points in the pitch space. The codebook index search starts with finding an open-loop estimate in the pitch space considering all dimensions and refining the open-loop estimate in a closed-loop search separately in each dimension based on the shaped lattice structure. The closed-loop search for the first subframe is for obtaining an absolute pitch period or a delta pitch while the closed-loop search for each of the other subframes is for obtaining a delta pitch for the respective subframe.

Claims

1. A method of coding a sound signal in a plurality of signal frames each having a pitch period indicative of the sound signal in the respective signal frame, wherein each signal frame comprises a plurality of signal segments each representing a dimension in a pitch space, and the sound signal in each of the signal segments is characterized by a pitch value, and wherein the pitch values are representable by a point distribution pattern characteristic of the sound signal in a lattice structure for defining codebook indices in the pitch space, said method comprising the steps of:

shaping the lattice structure based on the point distribution pattern; and

providing a codebook index representing the pitch value in each dimension of the pitch space according to the shaped lattice structure for facilitating coding of the sound signal.

2. The method of claim 1, further comprising the steps of:

obtaining an open-loop estimate of the pitch period by an open-loop search from the shaped lattice structure considering all of the dimensions of the pitch space; and

refining the open-loop estimate in each of the dimensions in the pitch space separately by a closed-loop search from the shaped lattice structure for obtaining a closed-loop search value indicative of the pitch value in the respective signal segment.

3. The method of claim 2, wherein the pitch value is indicative of a differential pitch period.

4. The method of claim 2, wherein the pitch value in at least one of the signal segments is indicative of an absolute pitch period and the pitch value in each of the remaining signal segments is indicative of a differential pitch period.

5. The method of claim 2, wherein the successive signal segments sequentially comprise a first signal segment and three second signal segments, and wherein the pitch value in the first signal segment is indicative of an absolute pitch period and the pitch value in each of the second signal segments is indicative of a differential pitch period.

6. The method of claim 2, wherein the signal segments are arranged in subframes.

7. The method of claim 6, wherein each of the signal frames comprises four subframes, and wherein the pitch value in each of the four subframes is indicative of a differential pitch period.

8. The method of claim 6, wherein the subframes include sequentially a first subframe and three second subframes and where the pitch value in the first subframe is an absolute pitch period, and the pitch value in each of the second subframes is a differential pitch period.

9. The method of claim 1, wherein the point density pattern is comprised of a plurality of regions in the shaped lattice structure and each of the regions is representable of a hypercube each having a plurality of edges comprising one or more lattice points of the shaped lattice structure, and wherein the codebook index is indicative of the number of lattice points on the edges of the hypercubes.

10. The method of claim 1, wherein the codebook index is provided by an encoding means to a decoding means having information indicative of the shaped lattice structure for allowing the decoding means to synthesize a speech signal from the codebook index based on the shaped lattice structure.

11. The method of claim 1, wherein the sound signal comprises a speech signal.

13. The apparatus of claim 12, wherein the pitch value is indicative of a differential pitch period.

14. The apparatus of claim 12, wherein the pitch value in at least one of the signal segments is indicative of an absolute pitch period and the pitch value in each of the remaining signal segments is indicative of a differential pitch period.

15. The apparatus of claim 12, wherein the signal segments are arranged in successive subframes.

16. The apparatus of claim 15, wherein the successive subframes sequentially comprise a first subframe and three second subframes, and wherein the pitch value in the first subframe is indicative of an absolute pitch period and the pitch value in each of the second subframes is indicative of a differential pitch period.

17. The apparatus of claim 15, wherein each of the signal frames comprises four subframes, and wherein the pitch value in each of the four subframes is indicative of a differential pitch period.

18. The apparatus of claim 12, wherein the point density pattern is comprised of a plurality of regions in the shaped lattice structure and each of the regions is representable of a hypercube each having a plurality of edges comprising one or more lattice points of the shaped lattice structure, and wherein the codebook index is indicative of the number of lattice points on the edges of the hypercubes.

12. An apparatus for encoding a sound signal in a plurality of signal frames each having a pitch period indicative of the sound signal in the respective signal frame, wherein each signal frame comprises a plurality of signal segments each representing a dimension in a pitch space, and the sound signal in each of the signal segments is characterized by a pitch value, and wherein the pitch values are representable by a point distribution pattern characteristic of the sound signal in a lattice structure for defining codebook indices in the pitch space, and the lattice structure is shaped based on the point distribution pattern for defining a shaped lattice structure, said apparatus comprising:

means, responsive to the sound signal, for obtaining an open-loop estimate of the pitch period by an open-loop search from the shaped lattice structure considering all of the dimensions of the pitch space for providing an open-loop search value indicative of the open-loop estimate; and

means, responsive to the open-loop search value, for refining the open-loop estimate in each of the dimensions in the pitch space separately by a closed-loop search from the shaped lattice structure for obtaining a closed-loop search value indicative of the pitch value in the respective signal segment.

19. A system for coding a sound signal in a plurality of signal frames each having a pitch period indicative of the sound signal in the respective signal frame, wherein each signal frame comprises a plurality of signal segments each representing a dimension in a pitch space, and the sound signal in each of the signal segments is characterized by a pitch value, and wherein the pitch values are representable by a point distribution pattern characteristic of the sound signal in a lattice structure for defining codebook indices in the pitch space, and the lattice structure is shaped based on the point distribution pattemfor defining a shaped lattice structure, said system comprising:

an encoder having;

means, responsive to the sound signal, for obtaining an open-loop estimate of the pitch period by an open-loop search from the shaped lattice structure considering all of the dimensions of the pitch space for providing an open-loop search value indicative of the open-loop estimate; and

means, responsive to the open-loop search value, for refining the open-loop estimate in each of the dimensions in the pitch space separately by a closed-loop search from the shaped lattice structure for obtaining a closed-loop search value indicative of the pitch value in the respective signal segment for providing information indicative of the shaped lattice structure and the codebook indices; and

a decoder having means, responsive to the information, for synthesizing a further sound signal from the codebook indices based on the shaped lattice structure.