Obviousness

Here is an analysis of the obviousness of US patent 8,374,358 under 35 U.S.C. § 103.

Person Having Ordinary Skill in the Art (PHOSITA)

A person having ordinary skill in the art (PHOSITA) for this patent would have a Master's degree in Electrical Engineering or a related field, with a focus on digital signal processing. This individual would have 2-3 years of practical experience in audio processing, particularly in the areas of adaptive filtering, noise cancellation, and microphone array processing (beamforming). A PHOSITA would be familiar with standard algorithms like the Normalized Least Mean Square (NLMS) algorithm and architectures like the Generalized Sidelobe Canceller (GSC).

Analysis of Independent Claim 1

Claim 1: A method for determining a noise reference signal for noise compensation and/or noise reduction...

This claim would have been obvious over the teachings of Gannot et al. ("Beamforming methods for multi-channel speech enhancement") in view of the knowledge of a PHOSITA regarding common techniques for improving numerical stability in adaptive filters.

1. Gannot et al. Disclosures:
   Gannot teaches a method for multi-channel speech enhancement using a blocking matrix within a GSC framework. The patent under analysis explicitly describes Gannot's approach, stating that it estimates the transfer functions between a wanted signal and the microphone signals (Col. 10, lines 40-44). The '358 patent presents Gannot's blocking matrix, which includes terms like -G2/G1, -G3/G1, etc. (Col. 10, lines 45-58). This structure directly corresponds to the system shown in FIG. 7 of the '358 patent, which aims to create a noise reference signal by filtering a first microphone signal and subtracting it from a second. To do this, the adaptive filter (715) must model the transfer function H = G2/G1.

   Therefore, Gannot teaches the core elements of claim 1:

   • Receiving a first audio signal (e.g., from microphone 1) and a second audio signal (e.g., from microphone 2).
   • Using adaptive filters to model acoustic transfer functions (G1, G2).
   • Combining these signals to obtain a noise reference signal where the wanted signal is minimized or "blocked".

2. The Problem with Gannot's Approach:
   The '358 patent itself identifies the critical weakness in the Gannot approach: "a blocking matrix comprises an inverse of a first transfer function modeling the transfer between the wanted signal and the first microphone signal, undesired artifacts in the noise reference signal may occur if the first transfer function approaches zero" (Col. 10, lines 60-64). This phenomenon, known as the "comb-filter" effect in room acoustics, causes the transfer function G1 to have zeros at certain frequencies. Attempting to compute 1/G1 at these frequencies leads to division by zero, causing instability and a poor-quality noise reference signal. This was a well-understood problem in the field of signal processing at the time of the invention.

3. Motivation to Modify Gannot:
   A PHOSITA, when implementing the system taught by Gannot, would immediately recognize the potential for instability due to the 1/G1 term. The motivation to solve this known problem would have been high, as it directly impacts the performance and reliability of the noise reduction system.

   The solution proposed in claim 1 of the '358 patent is to replace the single-filter structure which calculates S*G1 * (G2/G1) with a two-filter structure that calculates S*G1*H1 - S*G2*H2. The system then adapts H1 to model G2 and H2 to model G1 to cancel the wanted signal S.

   This modification represents a standard engineering technique for avoiding division and improving numerical stability. Reformulating an equation A/B into a cross-multiplication form (A*D - B*C = 0) is a common method taught in introductory signal processing and control theory to handle potential divisions by zero. A PHOSITA, motivated to solve the known instability of Gannot's approach, would have found it obvious to apply this standard technique. By replacing the problematic division with a more robust cross-multiplication structure using two adaptive filters instead of one, the PHOSITA would arrive at the method described in claim 1.

Analysis of Independent Claim 16

Claim 16: A method for processing an audio signal for noise compensation...

This claim would have been obvious over the combination of Gannot et al. (as modified above) and the teachings of Widrow et al. ("Adaptive noise cancellation: Principles and applications") or the established Generalized Sidelobe Canceller (GSC) framework (e.g., as described in Van Veen and Buckley).

Claim 16 adds the following steps to the method of claim 1:

• Filtering the generated noise reference signal with a third adaptive filter.
• Subtracting this filtered signal from the first audio signal to produce a noise-reduced output.

This is the classic structure of an adaptive noise canceller.

• Widrow is the seminal work in this field and teaches precisely this method: use a noise reference signal as the input to an adaptive filter, and subtract the filter's output from a primary signal to remove correlated noise.
• The GSC architecture (shown in FIG. 4 of the '358 patent) inherently includes this structure. The entire purpose of the blocking matrix (412) is to create noise reference signals that are then fed into an interference canceller (413), which is an array of adaptive filters. The output is then subtracted (414) from the main signal path.

A PHOSITA, having developed the improved noise reference signal generation method from claim 1 (by modifying Gannot), would have been motivated to use it for its intended purpose: noise cancellation. The most well-known and direct way to do this would be to integrate it into the standard Widrow or GSC framework. It would have been entirely obvious to take the superior noise reference signal and apply it within the established noise cancellation architecture, which is precisely what claim 16 describes.

Analysis of Independent Claim 20

Claim 20: A system for audio signal processing...

This system claim recites the hardware/software components necessary to carry out the method of claim 1: a receiver, two adaptive filters, and a subtractor. As the method of claim 1 is rendered obvious by Gannot in view of a PHOSITA's knowledge, a system claim that does little more than implement this obvious method in standard components would also be obvious. The motivation to create the system is the same as the motivation to perform the method: to generate a more stable and accurate noise reference signal. A PHOSITA would know how to implement adaptive filters and subtractors using common components like Digital Signal Processors (DSPs), FPGAs, or general-purpose computers, as listed in the patent's own description (Col. 14, lines 5-29).