Rate control for coding audio frames

• US 20040230425A1
• Filed: 05/16/2003
• Published: 11/18/2004
• Est. Priority Date: 05/16/2003
• Status: Abandoned Application

• Current Assignee: ESS Technology Incorporated (Semiconductor Holding Corp.)
• Original Assignee: Divio, Inc. (Semiconductor Holding Corp.)
• Inventors: Wang, Johnny, Chrysafis, Christos, Yu, Siu-Leong
• Application Number:
  US10/439,972
• Publication Number:
  US 20040230425A1
• Time in Patent Office: Days
• US Class Current: 704/223
• CPC Class Codes: G10L 19/035 Scalar quantisation

Abstract

To determine the number of bits to encode a current audio frame, in accordance with a running average of the common scale factors for all preceding audio frames, a common scale factor for the-current frame is computed. The current frame is encoded using the computed common scale factor if the same falls within a defined range, and the number of bits required to so encode the frame also falls within a calculated range. If, the number of bits required to so encode the frame falls outside the calculated range, an energy level associated with the current frame and a running average of the energies of all previous frames is computed, which in turn, are used to compute a target bit rate. Thereafter, a common scale factor which results in coding of the current frame using a number of bits close to the target bit rate is obtained.

Claims

1. A method for encoding of a current audio frame, the method comprising:

establishing minimum bit rate B_min and maximum bit rate B_max for the current frame, B_min and B_max being defined by a number of bits U_n stored in a buffer, maximum number of bits that the buffer is adapted to store U_max and an average bit rate B_avg;

establishing a running average of common scale factors θ

_n of audio frames preceding the current audio frame;

computing a common scale factor Q_n for the current frame using θ

_n;

encoding the current frame using Q_n if Q_n falls within a range defined by a minimum common scale factor value Q_min and a maximum common scale factor value Q_max; and

verifying that encoding the current frame using Q_n requires a number of bits B_n that falls within a range defined by B_min and B_max.

2. The method of claim 1 further comprising:

computing an energy level e_n associated with the current frame if B_n does not falls within B_min and B_max;

computing a running average of energies E_n of the audio frames preceding the current audio frame;

computing a target bit rate B_1n associated with the current frame using e_n and E_n;

determining a common scale factor Q_n that results in a number of bits close to B_1n when the current frame is encoded therewith.

3. The method of claim 2 wherein said B_min and B_max are defined in accordance with the following:

4. The method of claim 3 wherein the common scale factor Q_n is computed using the running average of common scale factors θ

_n of audio frames preceding the current audio frame in accordance with the following;

5. The method of claim 4 wherein said Q_min and Q_max are defined as follows:

6. The method of claim 5 wherein the energy level en associated with the current frame is defined by:

7. The method of claim 6 wherein the target bit rate B_1n is defined by:

8. The method of claim 2 further comprising:

updating the number of bits in the buffer after the current frame is encoded.

9. The method of claim 7 wherein Q_opt is determined using a bisection algorithm.

10. The method of claim 2 further comprising:

assigning a value to each of a plurality of scale factors q_k associated with the current audio frame.

11. The method of claim 2 wherein the current frame is received in a multi-channel system and wherein the common scale factor Q_n is used for encoding the current frame associated with each channel of the multi-channel system.

12. The method of claim 11 further comprising:

assigning a value to each of a plurality of scale factors q_k of the current associated with a first channel of the multi-channel system; and

defining offsets between scale factors of the first channel and those of other channels of the multi-channel system.

13. an apparatus adapted to set bit rate for encoding of a current audio frame, the apparatus comprising:

a module adapted to establish minimum bit rate B_min and maximum bit rate B_max for the current frame, B_min and B_max being defined by a number of bits U_n stored in a buffer, maximum number of bits that the buffer is adapted to store U_max and an average bit rate B_avg;

a module adapted to establish a running average of common scale factors θ

_n, of audio frames preceding the current audio frame;

a module adapted to compute a common scale factor Q_n for the current frame using θ

_n;

a module adapted to encode the current frame using Q_n if Q_n falls within a range defined by a minimum common scale factor value Q_n and a maximum common scale factor value Q_max; and

a module adapted to verify that encoding the current frame using Q_n requires a number of bits B_n that falls within a range defined by B_min and B_max.

14. The apparatus of claim 13 further comprising:

a module adapted to compute an energy level en associated with the current frame if B_n does not falls within B_min and B_max;

a module adapted to compute a running average of energies E_n of the audio frames preceding the current audio frame;

a module adapted to compute a target bit rate B_1n associated with the current frame using e_n and E_n; and

a module adapted to determine a common scale factor Q_opt that results in a number of bits close to B_1n when the current frame is encoded therewith.

15. The apparatus of claim 14 wherein said B_min and B_max are defined in accordance with the following:

16. The apparatus of claim 15 wherein the common scale factor Q_n is computed using the running average of common scale factors θ

_n of audio frames preceding the current audio frame in accordance with the following;

17. The apparatus of claim 16 wherein said Q_min and Q_max are defined as follows:

18. The apparatus of claim 17 wherein the energy level e_n associated with the current frame is defined by:

19. The apparatus of claim 18 wherein the target bit rate B_1n is defined by: