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AssigneeLake DSP Pty Limited
InventorDavid S. McGrath
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An improved method and apparatus for filtering an electronic environment with relatively high accuracy and efficiency and relatively short flow-through delay ("latency") is disclosed. Embodiments of the invention may be applied to digital filters implemented in software, hardware or a combination of both for applications such as audio filtering or electronic modelling of acoustic system characteristics. The method disclosed is broadly applicable in the field of signal processing and may be used to advantage, for example, in adaptive filtering; audio reverberation processing; adaptive echo cancellation; spatial processing; virtual reality audio; correlation, radar; radar pulse compression; deconvolution; seismic analysis; telecommunications; pattern recognition; robotics; 3D acoustic modelling; audio post production (including auralization and auto reverberant matching); audio equalization; compression; sonar; ultrasonics; secure communication systems; digital audio broadcast, acoustic analysis, surveillance; noise cancellation; and echo cancellation.
A method for building a digital filter with a long impulse response and low latency, built by operating a number of smaller component filters in parallel and combining their outputs by addition, with each component filter operating with a different delay such that the net operation of the ensemble of said component filters is the same as a single filter with a longer impulse response, and the latency of the ensemble is equal to the shortest latency of said component filters wherein one or more of said component filters is implemented as a time-domain finite impulse response filter, built with multiply and add operations, and the remainder of said component filters are implemented using a fast convolution method, such that time-domain filter(s) provides the lowest latency portion of the ensemble impulse, and fast convolution filter(s) provide longer filter components, wherein said fast convolution filters are built using the Discrete Fourier Transform or the Fast Fourier Transform.
A method for building a digital filter with a long impulse response and low latency built by operating a number of smaller component filters in parallel and combining their outputs by addition, with each component filter operating with a different delay such that the net operation of the ensemble of said component filters is the same as a single filter with a longer impulse response, and the latency of the ensemble is equal to the shortest latency of said component filters wherein one or more of said component filters is implemented as a time-domain finite impulse response filter, built with multiply and add operations, and the remainder of said component filters are implemented using a fast convolution method, such that time-domain filter provides the lowest latency portion of the ensemble impulse response, and fast-convolution filter provide the longer filter components, wherein said fast-convolution filters are built using a Modified Discrete Fourier Transform method comprising the steps of:
A composite electrical filter comprising a plurality of filter modules arranged to receive in parallel an incoming input signal for filtering, an output from each of said filter modules being summed to produce a composite filtered output signal, each of said filter modules having an impulse response that is a selected portion of said impulse response of the composite filter wherein the number of said filter module is N, comprising filters F.sub.1, F.sub.2 . . . F.sub.N and wherein filter modules F.sub.1 is a filter with a very low latency implemented with time domain techniques while all other filter modules F.sub.i are implemented with fast convolution means and these fast convolution filters F.sub.i are composed of a sequence of filters, each with longer filter length than its predecessor and hence each with longer latency, but still preserving the property that d.sub.i+1 =d.sub.i +l.sub.i whereby it is ensured that said composite filter F output formed by summing together N component filter outputs has an impulse response without any "holes" in it.
A digital filter having an impulse response that includes a low latency and a long filter length, said digital filter comprising a plurality of component filters each having an impulse response including a latency and a filter length, each of said component filter having an input connected to an input of said digital filter, and an output connected to a summing means for combining, by addition, each of said outputs to form an output of said digital filter such that the impulse response of said digital filter is the sum of the component impulse responses and the low latency is equal to the shortest one of the component latencies.
A digital filter comprising a plurality of filter modules arranged in parallel and each configured to receive an input signal for filtering, an output of each of said filter modules being summed to produce a composite filtered output signal, each of said filter modules having a corresponding filter length and a corresponding impulse response that is a selected portion of a desired impulse response of said digital filter, wherein the length of each of said filter modules is different, and wherein at least the shortest length filter module is a time-domain low latency filter configured to process at least first portions of said desired impulse response and the longer length filter module is a fast-convolution longer latency filter configured to process subsequent portions of said desired impulse response.
A Fourier transform processor adapted to transform strings of real numbers of use in digital filtering, said processor comprising:
A digital filter with a long impulse response and low latency comprising a smaller number of component filters in parallel and adding means for combining the output of said component filters, with each component filter operating with a different delay such that the net operation of said component filters is the same as a single filter with a longer impulse response, and the latency of said component filters is equal to a shortest latency of the said component filters wherein one or more of said component filters comprise a time-domain finite impulse response filter and multipliers and adders, and the remainder of said component filters comprise a fast convolution means, such that time-domain filter provide the lowest latency portion of said component filters impulse response, and the fast-convolution means provide the longer filter components and said fast-convolution means comprise Discrete Fourier Transformer or the Fast Fourier Transformer.
A digital filter with a long impulse response and low latency comprising a smaller number of component filters in parallel and adding means for combining the output of said component filters, with each component filter operating with a different delay such that the net operation of said component filters is the same as a single filter with a longer impulse response, and the latency of said component filters is equal to a shortest latency of the said component filters wherein one or more of said component filters comprise a time-domain finite impulse response filter and multipliers and adders, and the remainder of said component filters comprise a fast convolution means, such that time-domain filter provide the lowest latency portion of said component filters impulse response, and the fast-convolution means provide the longer filter components and said fast-convolution means comprise a Modified Discrete Fourier Transform processor comprising:
Dependencies are inferred from the claim text.