Lossless bandsplitting and bandjoining using allpass filters
AssigneeMQA Limited
InventorsPeter Graham Craven, Malcolm Law
Life of this patent
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Abstract
Methods and devices are described for lossless bandsplitting and bandjoining of streams of signal samples using allpass filtering. The bandsplitting operation reformats an original stream into two intermediate streams representing even and odd samples of the original stream, and then matrix filters these to provide two output substreams representing higher frequency components and lower frequency components of the original stream. Conversely, the bandjoining operation matrix filters two subband streams to provide two quantised intermediate substreams, and then interleaves the filtered streams to furnish an output stream, such that the intermediate substreams are the even and odd samples of the output stream.
Claims31
A method of splitting an original stream of quantised signal samples having an original sample rate into two output substreams of quantised signal samples having half the original sample rate, the two output substreams representing higher frequency components and lower frequency components of the original stream respectively, the method comprising the steps of:
- reformatting the original stream into two intermediate streams representing even and odd samples of the original stream respectively;
- filtering and matrixing the two intermediate streams to provide the two output substreams,
- wherein the step of filtering and matrixing comprises:
- using a quantiser to produce a quantised signal having samples;
- producing the quantised signal samples in reverse time order;
- and
- producing the quantised signal samples in dependence on feedback derived from previously produced samples of the quantised signal;
- and
- wherein each output substream is related to each intermediate stream by a respective transfer function comprising maximum phase poles.
A method of joining two subband streams of quantised signal samples each having a subband sample rate, the method furnishing an output stream of quantised signal samples having twice the subband sample rate, the output stream having higher frequency components and lower frequency components represented by the two subband streams respectively, the method comprising the steps of:
- matrixing and filtering the two subband streams to provide two quantised intermediate substreams;
- and,
- interleaving the two quantised intermediate to furnish the output stream, such that the intermediate substreams are respectively the even and odd samples of the output stream,
- wherein each intermediate substream is related to each subband stream by a respective transfer function that is infinite impulse response ‘IIR’ comprising maximum phase zeros;
- and
- wherein the step of matrixing and filtering incorporates quantisation configured to ensure that the output stream contains the information required to allow the quantised signal samples of each subband stream to be recovered exactly by a suitably initialised bandsplitter.
A bandsplitter comprising:
- an input adapted to receive an input stream of signal samples at a sample rate;
- two outputs adapted to furnish two output streams, each output stream having half the sampling rate of the input stream;
- a de-interleaving unit having an input and two outputs, wherein the input of the de-interleaving unit is coupled to the input of the bandsplitter, and wherein the outputs of the de-interleaving unit contain even-numbered and odd-numbered samples of the input stream respectively;
- two allpass filters each having a first input and an output, wherein the first input of each allpass filter is coupled to a respective output of the de-interleaving unit;
- and
- a lossless sum-and-difference unit having two inputs and two outputs, wherein each of the inputs to the sum-and-difference unit is coupled to a respective one of the outputs of the two allpass filters, and wherein each of the outputs of the sum-and-difference unit is coupled to a respective one of the outputs of the bandsplitter,
- wherein each allpass filter is adapted to receive the samples of the input stream in reverse time order.
A bandjoiner comprising:
- two inputs adapted to receive a first and a second stream of input quantised signal samples;
- an output adapted to furnish an output stream having a sampling rate twice that of each input stream;
- a sum-and-difference unit having two inputs and two outputs configured respectively as a sum output and a difference output;
- two allpass filters each having an first input and an output;
- and,
- an interleaving unit having two inputs and an output,
- wherein the inputs of the sum-and-difference unit are connected to the inputs of the bandjoiner;
- wherein the first input of each of the two allpass filters is connected to, respectively, the sum output and the difference output of the sum-and-difference unit;
- wherein the inputs of the interleaving unit are coupled to the outputs of the allpass filter;
- and,
- wherein the output of the interleaving unit is coupled to the output of the bandjoiner,
- wherein the bandjoiner is lossless.
Dependencies are inferred from the claim text.