US 6,246,345 B1 · Using gain-adaptive quantization and non-uniform symbol lengths for improved audio coding

Abstract

Techniques like Huffman coding can be used to represent digital audio signal components more efficiently using non-uniform length symbols than can be represented by other coding techniques using uniform length symbols Unfortunately, the coding efficiency that can be achieved by Huffman coding depends on the probability density function of the information to be coded and the Huffman coding process itself requires considerable processing and memory resources. A coding process that uses gain-adaptive quantization according to the present invention can realize the advantage of using non-uniform length symbols while overcoming the shortcomings of Huffman coding. In gain-adaptive quantization, the magnitudes of signal components to be encoded are compared to one or more thresholds and placed into classes according to the results of the comparison. The magnitudes of the components placed into one of the classes are modified according to a gain factor that is related to the threshold used to classify the components. Preferably, the gain factor may be expressed as a function of only the threshold value. Gain-adaptive quantization may be used to encode frequency subband signals in split-band audio coding systems. Additional features including cascaded gain-adaptive quantization, intra-frame coding, split-interval and non-overloading quantizers are disclosed.

Claims46

Dependent claims

A method for encoding an input signal that comprises:

receiving the input signal and generating a subband-signal block of subband-signal components representing a frequency subband of the input signal;
comparing magnitudes of the components in the subband-signal block with a threshold, placing each component into one of two or more classes according to component magnitude, and obtaining a gain factor;
applying the gain factor to the components placed into one of the classes to modify the magnitudes of some of the components in the subband-signal block;
quantizing the components in the subband-signal block;
and
assembling into an encoded signal control information conveying classification of the components and non-uniform length symbols representing the quantized subband-signal components.

3 more elements

An apparatus for encoding an input signal comprising:

an analysis filter having an input that receives the input signal and having an output through which is provided a subband-signal block of subband-signal components representing a frequency subband of the input signal;
a subband-signal block analyzer coupled to the analysis filter that compares magnitudes of the components in the subband-signal block with a threshold, places each component into one of two or more classes according to component magnitude, and obtains a gain factor,
a subband-signal component processor coupled to the subband-signal block analyzer that applies the gain factor to the components placed into one of the classes to modify the magnitudes of some of the components in the subband-signal block;
a first quantizer coupled to the subband-signal processor that quantizes the components in the subband-signal block having magnitudes modified according to the gain factor;
and
a formatter coupled to the first quantizer that assembles non-uniform length symbols representing the quantized subband-signal components and control information conveying classification of the components into an encoded signal.

3 more elements

Dependencies are inferred from the claim text.

Using gain-adaptive quantization and non-uniform symbol lengths for improved audio coding

Life of this patent

Using gain-adaptive quantization and non-uniform symbol lengths for improved audio coding

Life of this patent

Abstract

Claims46