Audio signal encoding apparatus and method and decoding apparatus and method which eliminate bit allocation information from the encoded data stream to thereby enable reduction of encoding/decoding delay times without increasing the bit rate

A method of encoding a digital audio signal to generate each of successive frames constituting an encoded bitstream by:

• applying mapping processing to convert a set of data samples of said digital audio signal which are to be conveyed by one frame into a plurality of sets of sub-band samples, said plurality of sets corresponding to respective ones of a plurality of sub-bands,
• operating on said sets of sub-band samples to calculate a plurality of scale factors respectively corresponding to said sub-bands,
• for each of said sub-bands, comparing said corresponding scale factor with a scale factor corresponding to said sub-band, of a preceding one of said frames, and when coincidence is detected as a result of said comparison, setting a scale factor flag which is predetermined as corresponding to said each sub-band to a first condition, while when non-coincidence is detected as a result of said comparison, setting said scale factor flag to a second condition,
• calculating respective sets of bit allocation information corresponding to each of said sub-bands, from said scale factors,
• for each of said sub-bands, quantizing the corresponding sub-band samples in accordance with the bit allocation information and the scale factor which have been calculated for said sub-band, and
• selecting each of said scale factors for which said coincidence was detected, encoding said selected scale factors and quantized sub-band samples, and assembling said each frame as a formatted bit sequence which includes respective sets of bits expressing said scale factor flags, said encoded selected scale factors, and said encoded quantized sub-band samples, while excluding said bit allocation information.

An apparatus for encoding a digital audio signal as a sequence of frames constituting an encoded bitstream, comprising:

• mapping means coupled to receive said digital audio signal, for applying a mapping operation to a set of samples of said digital audio signal which are to be conveyed by one frame, to obtain a plurality of sets of sub-band samples, said sets of sub-band samples corresponding to respective ones of a fixed plurality of sub-bands,
• scale factor calculation means for operating on said sets of sub-band samples to calculate a plurality of scale factors respectively corresponding to said sub-bands,
• bit allocation information calculation means for operating on said scale factors to calculate a plurality of sets of bit allocation information respectively corresponding to said sub-bands,
• quantization means for quantizing each of said sets of sub-band samples in accordance with the corresponding bit allocation information and scale factors, to obtain respective sets of quantized sub-band samples corresponding to said sub-bands,
• frame packing means for encoding said scale factors and quantized sub-band samples, and assembling said each frame as a formatted bit sequence which includes respective sets of bits expressing said encoded scale factors and said encoded quantized sub-band samples, while excluding said bit allocation information.

An apparatus for encoding a digital audio signal as a sequence of frames constituting an encoded bitstream, comprising:

• mapping means coupled to receive said digital audio signal, for applying a mapping operation to a set of samples of said digital audio signal which are to be conveyed by one frame, to obtain a plurality of sets of sub-band samples, said sets of sub-band samples corresponding to respective ones of a fixed plurality of sub-bands,
• scale factor calculation means for operating on said sets of sub-band samples to calculate a plurality of scale factors respectively corresponding to said sub-bands,
• scale factor judgement means including memory means having a plurality of memory locations predetermined as respectively corresponding to said sub-bands, for comparing each of said scale factors of a frame with a corresponding scale factor which is stored in said memory and is of a preceding one of said frames, for setting a scale factor flag which is predetermined as corresponding to said each scale factor to a first condition when coincidence is detected as a result of said comparison, and for setting said scale factor flag to a second condition, selecting said each scale factor to be encoded, and writing said scale factor into the corresponding one of said memory locations, when non-coincidence is detected as a result of said comparison,
• bit allocation information calculation means coupled to receive said scale factors from said scale factor calculation means, for operating on said scale factors of said each frame to calculate sets of bit allocation information which correspond to respective ones of said sub-bands,
• quantization means for quantizing said set of sub-band samples corresponding to a frame, by utilizing for the sub-band samples corresponding to each of said sub-bands a corresponding one of said sets of bit allocation information, and
• frame packing means for encoding said ones of the scale factors which have been selected to be encoded, and encoding said quantized sub-band samples, and assembling said each frame as a formatted bit sequence which includes respective sets of bits expressing said scale factor flags, said encoded scale factors and said encoded quantized sub-band samples, while excluding said bit allocation information.

An encoding and decoding system for transmitting a digital audio signal as an encoded bitstream, comprising in combination:

• a digital audio signal encoding apparatus having
• mapping means coupled to receive said digital audio signal, for applying a mapping operation to a set of samples of said digital audio signal which are to be conveyed by one frame, to obtain a plurality of sets of sub-band samples, said sets of sub-band samples corresponding to respective ones of a fixed plurality of sub-bands,
• scale factor calculation means for operating on said sets of sub-band samples to calculate a plurality of scale factors respectively corresponding to said sub-bands,
• bit allocation information calculation means for operating on said scale factors to calculate a plurality of sets of bit allocation information respectively corresponding to said sub-bands,
• quantization means for quantizing each of said sets of sub-band samples in accordance with the corresponding bit allocation information and scale factors, to obtain respective sets of quantized sub-band samples corresponding to said sub-bands,
• frame packing means for encoding said scale factors and quantized sub-band samples, and assembling said each frame as a formatted bit sequence which includes respective sets of bits expressing said encoded scale factors and said encoded quantized sub-band samples, while excluding said bit allocation information;
• and
• a digital audio signal decoding apparatus having
• frame unpacking means for operating on each of said frames to separate said scale factors and said quantized sub-band samples from said each frame,
• bit allocation information calculation means coupled to receive said scale factors from said frame unpacking means, for operating on said scale factors of said each frame to calculate said bit allocation information,
• data reconstruction means coupled to receive said quantized samples and said bit allocation information of said each frame, for operating on said bit allocation information and said scale factors to recover a set of dequantized sub-band samples,
• inverse mapping means for applying inverse transform processing to said dequantized sub-band samples, to recover a set of successive samples of said digital audio signal.

An encoding and decoding system for transmitting a digital audio signal as an encoded bitstream, comprising in combination

• a digital audio signal encoding apparatus having
• mapping means coupled to receive said digital audio signal, for applying a mapping operation to a set of samples of said digital audio signal which are to be conveyed by one frame, to obtain a plurality of sets of sub-band samples, said sets of sub-band samples corresponding to respective ones of a fixed plurality of sub-bands,
• scale factor calculation means for operating on said sets of sub-band samples to calculate a plurality of scale factors respectively corresponding to said sub-bands,
• scale factor judgement means including memory means having a plurality of memory locations predetermined as respectively corresponding to said sub-bands, for comparing each of said scale factors of a frame with a corresponding scale factor which is stored in said memory and is of a preceding one of said frames, for setting a scale factor flag which is predetermined as corresponding to said each scale factor to a first condition when coincidence is detected as a result of said comparison, and for setting said scale factor flag to a second condition, selecting said each scale factor to be encoded, and writing said scale factor into the corresponding one of said memory locations, when non-coincidence is detected as a result of said comparison,
• bit allocation information calculation means coupled to receive said scale factors from said scale factor calculation means, for operating on said scale factors of said each frame to calculate sets of bit allocation information which correspond to respective ones of said sub-bands,
• quantization means for quantizing said set of sub-band samples corresponding to a frame, by utilizing for the sub-band samples corresponding to each of said sub-bands a corresponding one of said sets of bit allocation information, and
• frame packing means for encoding said ones of the scale factors which have been selected to be encoded, and encoding said quantized sub-band samples, and assembling said each frame as a formatted bit sequence which includes respective sets of bits expressing said scale factor flags, said encoded scale factors and said encoded quantized sub-band samples, while excluding said bit allocation information;
• and
• a digital audio signal decoding apparatus having
• frame unpacking means for operating on each of said frames to separate said scale factor flags, said selected scale factors and said quantized sub-band samples from said each frame,
• scale factor restoration means including memory means having a plurality of memory locations predetermined as respectively corresponding to said sub-bands, coupled to receive said scale factor flags and said selected scale factors of said each frame, for judging the condition of each of said scale factor flags and when scale factor flag is judged to be in said first condition, reading out a scale factor from a memory location corresponding to the sub-band of said scale factor flag, and outputting said scale factor, while when said scale factor flag is judged to be in said second condition, outputting the corresponding one of said selected scale factors conveyed by said each frame, and writing said corresponding one of the selected scale factors into said memory location,
• bit allocation information calculation means coupled to receive said scale factors produced from scale factor restoration means, for operating on said scale factors of said each frame to calculate said bit allocation information,
• data reconstruction means coupled to receive said quantized samples and said bit allocation information of said each frame, for operating on said bit allocation information and said scale factors to recover a set of dequantized sub-band samples, and
• inverse mapping means for applying inverse transform processing to said dequantized sub-band samples, to recover a set of successive samples of said digital audio signal.