A method of encoding one or more parent blocks of values, the number of values being the length of each block, the method comprising for each parent block: (a) determining a first sum of values in the parent block; (b) splitting the parent block into smaller subblocks; (c) for at least one of the subblocks, determining a second sum of the values in the subblock, selecting a likelihood table from the plurality of likelihood tables based on said first sum of values in the parent block and encoding the second sum using the likelihood table; (d) designating each subblock a parent block; (e) carrying out steps (a), (b), (c) and (d) until at least one parent block reaches a predetermined condition.
1. A method for encoding speech according to a source filter model, whereby speech is modelled to comprise a source signal filtered by a time varying filter, the method comprising:
receiving, using a computing device, a speech signal;
deriving, using the computing device, from the speech signal a frame of excitation quantization indices, each index being represented by a value and the frame comprising a plurality of blocks; and
encoding, using the computing device, one or more parent blocks of values, the number of values being the length of each block, the method comprising for each parent block:
(a) determining a first sum of values in the parent block;
(b) splitting the parent block into smaller subblocks;
(c) for at least one of the subblocks, determining a second sum of the values in the subblock, selecting a likelihood table from the plurality of likelihood tables based on said first sum of values in the parent block and encoding the second sum using the likelihood table;
(d) designating each subblock a parent block;
(e) carrying out steps (a), (b), (c) and (d) until at least one parent block reaches a predetermined condition.
2. The method of claim 1 , wherein the likelihood table is selected based on also the length of the parent block.
3. The method of claim 1 , wherein said splitting comprises splitting the parent block into smaller subblocks of equal size.
4. The method of claim 1 , wherein said encoding comprises entropy encoding.
5. The method of claim 1 , wherein said encoding comprises arithmetic encoding.
6. The method of claim 1 , wherein said predetermined condition is that all subblocks have a length of one.
7. The method of claim 1 , wherein said predetermined condition is that the sum of the values in the first subblock equals zero.
8. The method of claim 1 , wherein said determining comprises using a known value for the first sum.
9. The method of claim 1 , wherein said determining comprises determining a sum of the values of summation.
10. The method of claim 1 further comprising storing an encoded result of step (b), and each step (d) until a final result is generated after the final splitting and encoding step for the block.
11. A system for encoding speech according to a source filter model, whereby speech is modelled to comprise a source signal filtered by a time varying filter, the system comprising:
means for receiving a speech signal:
means for deriving from the speech signal a frame of excitation quantization indices, each index being represented by a value and the frame comprising a plurality of blocks; and
an encoder stored on a hardware storage device comprising:
means for splitting the parent block into smaller subblocks;
means for summing the values in a subblock to generate a sum;
a store holding likelihood tables, each likelihood table holding for each possible sum of values a probability associated with that sum;
means for encoding the sum of the values in the subblock using a likelihood table located in the store;
means for selecting from the store of likelihood tables a table based on the sum of the parent subblock, said encoding means being arranged to encode the sum of a subblock split from the parent block based on the selected likelihood table; and
storage means for holding the result of said encoding.
12. The system of claim 11 , wherein said means for selecting comprises means for selecting the table based also on the length of the parent block.
13. The system of claim 11 , wherein said means for splitting comprises means for splitting the parent block into smaller subblocks of equal size.
14. The system of claim 11 , wherein said means for encoding comprises means for entropy encoding.
15. The system of claim 11 , wherein said means for encoding comprises means for arithmetic encoding.
16. A system for decoding speech according to a source filter model, whereby speech is modelled to comprise a source signal filtered by a time varying filter, the system comprising:
means for receiving an encoded speech signal including a frame of excitation quantization indices, each index being represented by a value and the frame comprising a plurality of blocks; and
a decoder stored on a hardware storage device comprising:
means for obtaining a first sum of value in the parent block;
means for splitting a parent block into smaller subblocks;
means for selecting a likelihood table from a plurality of stored tables based on the first sum of the values in the parent block, each likelihood table holding for each possible second sum of values in the subblock a probability associated with that sum; and
means for decoding the bitstream based on the likelihood table to generate the second sum of values for the subblock.