Fast frame optimization in an audio encoder

• US 6,952,677 B1
• Filed: 04/15/1998
• Issued: 10/04/2005
• Est. Priority Date: 04/15/1998
• Status: Expired due to Term

• Current Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV)
• Inventors: George, Sapna, Alvarez-Tinoco, Antonio Mario, Absar, Mohammed Javed
• Primary Examiner(s): To, Doris H.
• Assistant Examiner(s): Opsasnick, Michael N.
• Application Number:
  US09/673,463
• Time in Patent Office: 2,729 Days
• Field of Search: 704/229, 704/230, 704500-504, 708/203
• US Class Current: 704/500
• CPC Class Codes: G10L 19/002 Dynamic bit allocation for perceptual audio coders G10L19/032

Abstract

In a transform encoder for audio data, encoded data in the form of mantissas, exponents and coupling data is packed into fixed length frames in an output bitstream. The fields within the frame for carrying the different forms of data are variable in length, and apace within the frame must be allocated between them to fit all of the required information into the frame. The space required by the various data types depends on certain encoding parameters, which are calculated for a particular frame before the data is encoded, thus ensuring that the encoded data will fit into the frame before the computationally expensive encoding process is carried out. Information in relation to, for example, transform length, coupling parameters and exponent strategy are determined, which allows the space required for the coupling and exponent data to be calculated. The mantissa encoding parameters can then be iteratively determined so that the encoded mantissas will fit into the frame with the other encoded data. The determined encoding parameters are stored and the audio data is encoded according to those parameters after it has been determined that the encoded data will fit into the frame.

Claims

1. A method of processing input audio data for compression into an encoded bitstream comprising a series of fixed size frames, each of the fixed size frames having a plurality of variable size fields containing coded data of different types, the method including the steps of:

receiving input data to be coded into a frame of the output bitstream;

preprocessing the input data to determine at least one first coding parameter to be used for coding the input data into at least one of the variable size fields in the frame, wherein the value of the at least one first coding parameter affects the data space size required for the at least one variable size field;

storing the at least one first coding parameter determined in the preprocessing step;

allocation data space in the frame for at least one other of the variable size fields on the basis of the determined at least one first coding parameter;

determining at least one second coding parameter for coding data into the at least one other variable sized field on the basis of said allocated space; and

coding the input data into the variable sized fields of the frame using the first and second coding parameters, wherein a transform coding technique is employed such that the coded data includes exponent data and mantissa data, wherein the input audio data includes a plurality of channels and the coded data includes coupling parameters relating to the plurality of channels.

2. A method as claimed in claim 1, wherein the frame is arranged in a plurality of data blocks, each block having the plurality of variable size fields corresponding to different coded data types.

3. A method as claimed in claim 1, wherein the at least one second coding parameter comprises at least one parameter required for coding the mantissa data.

4. A method as claimed in claim 3, wherein the at least one first coding parameter includes an exponent strategy for coding said exponent data.

5. A method as claimed in claim 3, wherein the at least one first coding parameter includes a block switch parameter indicating a transform length for the transform encoding technique.

6. A method as claimed in claim 5, wherein the block switch parameter is determined according to the detection of transients in the input audio data.

7. A method as claimed in claim 1, wherein the input audio data is coded substantially in accordance with the AC-3 audio coding standard.

8. A method of processing input audio data for compression into an encoded bitstream comprising a series of fixed size frames, each of the fixed size frames having a plurality of variable size fields containing coded data of different types, the method including the steps of:

receiving input data to be coded into a frame of the output bitstream;

preprocessing the input data to determine at least one first coding parameter to be used for coding the input data into at least one of the variable size fields in the frame, wherein the value of the at least one first coding parameter affects the data space size required for the at least one variable size field;

storing the at least one first coding parameter determined in the preprocessing step;

allocation data space in the frame for at least one other of the variable size fields on the basis of the determined at least one first coding parameter;

determining at least one second coding parameter for coding data into the at least one other variable sized field on the basis of said allocated space; and

coding the input data into the variable sized fields of the frame using the first and second coding parameters, wherein a transform coding technique is employed such that the coded data includes exponent data and mantissa data wherein the at least one second coding parameter comprises at least one parameter required for coding the mantissa data, and wherein the at least one first coding parameter includes a coupling strategy between multiple channels in the input audio data.

9. A method for transform encoding audio data having a plurality of channels for transmission or storage in a fixed length frame of an encoded data bitstream, the frame including variable length fields for encoded exponents, encoded mantissas and coupling data, the method including the steps of:

obtaining input audio data for a frame;

determining a transform length parameter for the audio data;

determining coupling parameters for the audio data;

determining an exponent strategy for the audio data;

calculating space required in the frame for the exponent and coupling data fields on the basis of the determined transform length parameter, coupling parameters and exponent strategy;

calculating space available in the frame for the encoded mantissa field according to the calculated space required in the frame for the exponent and coupling data fields;

determining a mantissa encoding parameter on the basis of the calculated available space; and

encoding the audio data into exponent data, mantissa data and coupling data utilizing the transform length parameter, coupling parameters, exponent strategy and mantissa encoding parameter, and packing the encoded audio data into the respective fields in the frame.

10. A method as claimed in claim 9, wherein the mantissa encoding parameter is determined according to an iterative bit allocation algorithm utilizing a power spectral density function and a raw masking curve function for the input audio data, as well as the calculated available space.

11. A method as claimed in claim 9, wherein the audio data is encoded substantially in accordance with the AC-3 audio coding standard, and wherein two mantissa encoding parameters are determined, being csnroffset and fsnroffset.

12. A method as claimed in claim 9 wherein the transform length parameter is determined by a block switch parameter and the block switch parameter is determined by the detection of a transient in the audio input data.

13. A transform audio encoder for encoding audio data having a plurality of channels for transmission or storage in a fixed length frame of an encoded data bitstream, the frame including variable length fields for encoded exponents, encoded mantissas and coupling data, the encoder including:

an input buffer for storing input audio data for a frame;

means for determining a transform length parameter, coupling parameters and an exponent strategy for the audio data;

means for calculating space required in the frame for the exponent and coupling data fields on the basis of the determined transform length parameter, coupling parameters and exponent strategy;

means for calculating space available in the frame for the encoded mantissa field according to the calculated space required in the frame of the exponent and coupling data fields;

means for determining a mantissa encoding parameter on the basis of the calculated available space; and

encoding means for encoding the audio data into exponent data, mantissa data and coupling data utilizing the transform length parameter, coupling parameters, exponent strategy and mantissa encoding parameter, and packing the encoded audio data into the respective fields in the frame.

14. A transform audio encoder as claimed in claim 13, including a storage means for storing the transform length parameter, coupling parameters, exponent strategy and mantissa encoding parameter for use by the encoding means in encoding the audio data.