Prior art — US Patent 8374358

Prior Art Analysis for US Patent 8,374,358

This analysis details the prior art references cited by the USPTO examiner during the prosecution of US patent 8,374,358. Each reference is examined for its potential to anticipate the claims of the '358 patent under 35 U.S.C. § 102.

A prior art reference anticipates a patent claim if it discloses, either explicitly or inherently, each and every element of that claim. The '358 patent's independent claims (1, 16, and 20) center on a method and system for generating a noise reference signal by using two adaptive filters on two separate audio signals and adapting the filters to minimize a "wanted" signal component in the combined output.

U.S. Patent Citations

1. US Patent 7,248,701 B2

Full Citation: US Patent 7,248,701 B2, "System and method for adaptively generating a noise reference in a multi-microphone environment," filed by Chen et al. on February 15, 2005, and issued on July 24, 2007. Assigned to Sony Corporation.
Brief Description: This patent describes a system for generating a noise reference signal for noise cancellation in a multi-microphone setup. It uses a primary microphone signal and one or more secondary microphone signals. An adaptive filter is used to model the transfer function between the desired speech signal at the primary and secondary microphones. This model is then used to subtract the estimated speech component from a secondary microphone signal, thereby creating a noise reference.
Potential Anticipation: This reference is highly relevant. It discloses receiving multiple audio signals, using an adaptive filter to estimate a wanted signal component, and subtracting it to generate a noise reference. However, a key distinction from claim 1 of the '358 patent is that the '701 patent appears to use a single adaptive filter structure to model the relationship and create the noise reference (as depicted in its figures and description), rather than filtering both the first and second audio signals with separate adaptive filters which are then combined. The '358 patent's use of two distinct adaptive filters (H1 and H2), one for each signal path, which are adapted to model the cross-path transfer functions (G2 and G1 respectively), is a specific implementation not clearly taught in '701. Therefore, while close, it may not anticipate claim 1's requirement of filtering both signals with distinct adaptive filters before combination.

2. US Patent 7,515,708 B2

Full Citation: US Patent 7,515,708 B2, "Method and apparatus for improving signal quality from a microphone array," filed by Bitzer et al. on August 31, 2005, and issued on April 7, 2009. Assigned to Starkey Laboratories, Inc.
Brief Description: This patent details a method for improving the signal-to-noise ratio in microphone arrays, particularly for hearing aids. It describes forming a beamformed signal and then using an adaptive filter to remove noise. The system can adaptively switch between different beamforming modes. The noise reference for the adaptive filter is generated by creating a null in the direction of the desired sound source.
Potential Anticipation: The '708 patent discusses creating a noise reference by steering a null towards the speaker, which is a form of blocking the wanted signal. It uses adaptive filtering to then cancel noise from a primary signal. However, it does not explicitly describe the '358 patent's core novelty: receiving a first and second audio signal, filtering the first with a first adaptive filter, filtering the second with a second adaptive filter, and then combining the two filtered outputs. The '708 patent's method of generating the noise reference appears to be based on beamforming techniques rather than the specific dual-adaptive-filter structure claimed in the '358 patent. Thus, it is unlikely to anticipate the independent claims.

3. US Patent 7,929,915 B2

Full Citation: US Patent 7,929,915 B2, "Apparatus and method for canceling noise," filed by Kim et al. on December 22, 2005, and issued on April 19, 2011. Assigned to LG Electronics Inc.
Brief Description: This patent discloses a noise-canceling apparatus that uses two microphones. The signal from one microphone is delayed and then processed with an adaptive filter. The output is subtracted from the other microphone's signal to cancel out the noise. The system aims to estimate the noise in the primary signal based on the secondary signal.
Potential Anticipation: This reference describes a classic adaptive noise cancellation setup with two microphones and one adaptive filter, similar to the prior art system shown in FIG. 7 of the '358 patent itself. It does not teach the use of two adaptive filters, one for each input signal, which are then combined. The method described in claim 1, involving filtering the first audio signal with a first adaptive filter and the second audio signal with a second adaptive filter, is absent. Therefore, this patent does not anticipate the independent claims of the '358 patent.

4. US Patent Application Publication 2008/0285786 A1

Full Citation: US 2008/0285786 A1, "Method and arrangement for noise reduction," filed by Baumgarte et al. on May 16, 2007, and published on November 20, 2008.
Brief Description: This publication describes a noise reduction system using a microphone array. It focuses on creating a noise reference signal by forming a beam that has a null directed at the desired sound source. This noise reference is then adaptively filtered and subtracted from a main signal beam to reduce noise.
Potential Anticipation: Similar to the '708 patent, this reference focuses on beamforming techniques to generate a noise reference by creating a null. This is a different approach from the specific two-signal, two-filter architecture claimed in the '358 patent. It does not teach filtering both a first and second audio signal with their own respective adaptive filters and then combining the results. Consequently, it does not anticipate claims 1, 16, or 20.

Non-Patent Literature

1. "A robust adaptive beamformer for microphone arrays with a blocking matrix using constrained adaptive filters" by O. Hoshuyama et al., IEEE Transactions on Signal Processing, Vol. 47, No. 10, October 1999.

Brief Description: This article, cited in the '358 patent's background section, describes a generalized sidelobe canceller (GSC) with an adaptive blocking matrix. The goal is to create noise references that are free of the desired signal. It uses adaptive filters within the blocking matrix to subtract the estimated desired signal from microphone inputs.
Potential Anticipation: This reference is highly relevant and describes an advanced method for generating a noise reference. The system in Hoshuyama uses a primary beamformed signal and subtracts filtered versions of it from the individual microphone signals. This can be interpreted as having a filter for each channel. However, the architecture is that of a GSC, where a reference signal (the beamformer output) is filtered and subtracted from other signals. The '358 patent claims a more symmetric structure where two arbitrary audio signals are each passed through their own adaptive filters, and the outputs are combined. The adaptation goal in the '358 patent is to make the transfer function of the first filter model the transfer characteristics of the second signal path, and vice versa. This specific approach of creating a pole-free transfer function to block the wanted signal is the novel step argued in the '358 patent. While Hoshuyama is very close, the specific topology and adaptation goal as described in claim 1 may be considered distinct.

In summary, while the cited prior art addresses the same general problem of creating a noise reference signal in multi-microphone systems, none of the references appear to explicitly disclose the specific architecture recited in the independent claims of US patent 8,374,358: filtering a first audio signal with a first adaptive filter, filtering a second audio signal with a second adaptive filter, and combining the two filtered signals, where both filters are adapted to minimize the wanted signal component in the final combination. This specific dual-filter structure for creating a blocking matrix without introducing potential instability (poles) appears to be the key point of novelty.