Naveen Thumpudi

Quantization matrices based on critical band pattern information for digital audio wherein quantization bands differ from critical bands

Quantization matrices facilitate digital audio encoding and decoding. An audio encoder generates and compresses quantization matrices; an audio decoder decompresses and applies the quantization matrices. The invention includes several techniques and tools, which can be used in combination or separately. For example, the audio encoder can generate quantization matrices from critical band patterns for blocks of audio data. The encoder can compute the quantization matrices directly from the critical band patterns, which can be computed from the same audio data that is being compressed. The audio encoder/decoder can use different modes for generating/applying quantization matrices depending on the coding channel mode of multi-channel audio data. The audio encoder/decoder can use different compression/decompression modes for the quantization matrices, including a parametric compression/decompression mode.

Hybrid low bitrate audio coding using adaptive gain shape vector quantization

Audio coding at low bitrates typically suffers from artifacts caused by bandwidth truncation. In this paper we present a novel scheme to code audio signals at low bitrates which uses a traditional scalar quantization followed by entropy coding to code some portions of the spectrum (typically the lower portion). The other portions (typically the higher portions) of the spectrum are coded at a low bitrate using an adaptive gain shape vector quantizer where the codebook for vector quantization is formed by unmodified or modified versions of the portions of the spectrum which have already been coded. Fixed pre-trained codebooks are also available for use in certain cases. The use of such a scheme results in an audio codec which has been shown to be among the best audio codecs available at low bitrates. In addition, the decoder complexity of this audio codec is significantly lower than any other codec of equal quality at low bitrates.