# US 10,311,884 B2 · Advanced quantizer > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,311,884 B2 - Document ID: US10311884B2 - Status: Granted - Kind: B2 - Application number: 15/933,108 - Filed: 2018-03-22 - Published: 2018-07-26 - Granted: 2019-06-04 - Earliest claimed: 2013-04-05 - Assignees: Dolby International AB - Applicants: Dolby International AB - Inventors: Janusz Klejsa; Lars Villemoes; Per Hedelin - Web page: https://patentgrep.com/patent/US10311884B2 ## CPC - G10L 19/035: Scalar quantisation - G10L 19/005: Correction of errors induced by the transmission channel, if related to the coding algorithm - G10L 19/028: Noise substitution, i.e. substituting non-tonal spectral components by noisy source (comfort noise for discontinuous speech transmission G10L19/012) - G10L 19/20: using sound class specific coding, hybrid encoders or object based coding - G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING ## Abstract The present document relates an audio encoding and decoding system (referred to as an audio codec system). In particular, the present document relates to a transform-based audio codec system which is particularly well suited for voice encoding/decoding. A quantization unit configured to quantize a first coefficient of a block of coefficients is described. The block of coefficients comprises a plurality of coefficients for a plurality of corresponding frequency bins. The quantization unit is configured to provide a set of quantizers. The set of quantizers comprises a plurality of different quantizers associated with a plurality of different signal-to-noise ratios, referred to as SNR, respectively. The plurality of different quantizers includes a noise-filling quantizer; one or more dithered quantizers; and one or more un-dithered quantizers. The quantization unit is further configured to determine an SNR indication indicative of a SNR attributed to the first coefficient, and to select a first quantizer from the set of quantizers, based on the SNR indication. In addition, the quantization unit is configured to quantize the first coefficient using the first quantizer. ## Claims ### Claim 1 A transform-based audio encoder configured to encode an audio signal into a bitstream; the encoder comprising hardware implementing a quantization unit configured to determine a plurality of quantization indices by quantizing a plurality of coefficients from a block of coefficients using a dithered quantizer; wherein the plurality of coefficients is associated with a plurality of corresponding frequency bins; wherein the block of coefficients is derived from the audio signal; a dither generator configured to select one of M pre-determined dither realizations, and configured to generate a plurality of pseudo-random dither values for quantizing the plurality of coefficients, respectively, based on the selected dither realization; wherein M is an integer greater than one; and an entropy encoder configured to select a codebook from M pre-determined codebooks, and configured to entropy encode the plurality of quantization indices using the selected codebook; wherein the M pre-determined codebooks are associated with the M pre-determined dither realizations, respectively; wherein the M pre-determined codebooks have been trained using the M pre-determined dither realizations, respectively; wherein the entropy encoder is configured to select the codebook associated with the dither realization selected by the dither generator; and wherein the transform-based audio encoder is configured to insert coefficient data indicative of the entropy encoded quantization indices into the bitstream. ### Claim 2 (depends on 1) The transform-based speech encoder of claim 1, wherein the number M of pre-determined dither realizations is 10, 5, 4 or less. ### Claim 3 (depends on 1) The transform-based speech encoder of any of claims 1, wherein the M pre-determined codebooks comprise variable-length Huffman codewords. ### Claim 4 A transform-based audio decoder configured to decode a bitstream to provide a reconstructed audio signal; the decoder comprising hardware implementing a dither generator configured to select one of M pre-determined dither realizations, and configured to generate a plurality of dither values based on the selected dither realization; wherein M is an integer greater than one; wherein the plurality of dither values is used by an inverse quantization unit comprising a dithered quantizer configured to determine a corresponding plurality of quantized coefficients based on a corresponding plurality of quantization indices; and an entropy decoder configured to select a codebook from M pre-determined codebooks and configured to entropy decode coefficient data from the bitstream using the selected codebook, to provide the plurality of quantization indices; wherein the M pre-determined codebooks are associated with the M pre-determined dither realizations, respectively; wherein the M pre-determined codebooks have been trained using the M pre-determined dither realizations, respectively; and wherein the entropy decoder is configured to select the codebook associated with the dither realization selected by the dither generator; wherein the entropy decoder is configured to determine the reconstructed audio signal based on the plurality of quantized coefficients. ### Claim 5 A method for encoding an audio signal into a bitstream; the method comprising determining a plurality of quantization indices by quantizing a plurality of coefficients from a block of coefficients using a dithered quantizer; wherein the plurality of coefficients is associated with a plurality of corresponding frequency bins; wherein the block of coefficients is derived from the audio signal; selecting one of M pre-determined dither realizations; generating a plurality of dither values for quantizing the plurality of coefficients, based on the selected dither realization; wherein M is an integer greater one; selecting a codebook from M pre-determined codebooks; entropy encoding the plurality of quantization indices using the selected codebook; wherein the M pre-determined codebooks are associated with the M pre-determined dither realizations, respectively; wherein the M pre-determined codebooks have been trained using the M pre-determined dither realizations, respectively; wherein the selected codebook is associated with the selected dither realization; and inserting coefficient data indicative of the entropy encoded quantization indices into the bitstream. ### Claim 6 A method for decoding a bitstream to provide a reconstructed audio signal; the method comprising selecting one of M pre-determined dither realizations; generating a plurality of dither values based on the selected dither realization; wherein M is an integer greater one; wherein the plurality of dither values is used by an inverse quantization unit comprising a dithered quantizer to determine a corresponding plurality of quantized coefficients based on a corresponding plurality of quantization indices; selecting a codebook from M pre-determined codebooks; entropy decoding coefficient data from the bitstream using the selected codebook, to provide the plurality of quantization indices; wherein the M pre-determined codebooks are associated with the M pre-determined dither realizations, respectively; wherein the M pre-determined codebooks have been trained using the M pre-determined dither realizations, respectively; and wherein the selected codebook is associated with the selected dither realization; and determining the reconstructed audio signal based on the plurality of quantized coefficients. ### Claim 7 A method for encoding a speech signal into a bitstream; the method comprising: receiving a plurality of sequential blocks of transform coefficients comprising a current block and one or more previous blocks; wherein the plurality of sequential blocks is indicative of samples of the speech signal; determining a current block of flattened transform coefficients by flattening the corresponding current block of transform coefficients using a corresponding current block envelope; determining a current block of estimated flattened transform coefficients based on one or more previous blocks of reconstructed transform coefficients and based on one or more predictor parameters; wherein the one or more previous blocks of reconstructed transform coefficients have been derived from the one or more previous blocks of transform coefficients; determining a current block of prediction error coefficients based on the current block of flattened transform coefficients and based on the current block of estimated flattened transform coefficients; and determining coefficient data for the bitstream based on quantization indices associated with the current block of prediction error coefficients; encoding the speech signal into the bitstream based on the coefficient data. ### Claim 8 A method for decoding a bitstream to provide a reconstructed speech signal; the method comprising determining a current block of estimated flattened transform coefficients based on one or more previous blocks of reconstructed transform coefficients and based on one or more predictor parameters derived from the bitstream; determining a current block of quantized prediction error coefficients based on coefficient data comprised within the bitstream; determining a current block of reconstructed flattened transform coefficients based on the current block of estimated flattened transform coefficients and based on the current block of quantized prediction error coefficients; determining a current block of reconstructed transform coefficients by providing the current block of reconstructed flattened transform coefficients with a spectral shape, using a current block envelope; and determining the reconstructed speech signal based on the current block of reconstructed transform coefficients.