US 8320575

A concise summary of US Patent 8,320,575 is as follows:

Title: Efficient audio signal processing in the sub-band regime

Assignee: Cerence Operating Co.

Inventors: Gerhard Uwe Schmidt, Hans-Jörg Köpf, Günther Wirsching

Filing Date: September 30, 2008

Issue Date: November 27, 2012

Abstract:
A signal processing system enhances an audio signal. The audio signal is divided into audio sub-band signals. Some audio sub-band signals are excised. Other audio sub-band signals are processed to obtain enhanced audio sub-band signals. At least a portion of the excised audio sub-band signals are reconstructed. The reconstructed audio sub-band signals are synthesized with the enhanced audio sub-band signals to form an enhanced audio signal.

Plain-Language Overview of Independent Claims:

Claim 1: This claim describes a method for processing an audio signal to improve its quality. The core idea is to break the audio signal down into different frequency bands (sub-bands), remove some of these bands to make the processing more efficient, enhance the remaining bands, recreate the removed bands, and then combine everything back into a single, improved audio signal.

Claim 10: This claim outlines a similar method to claim 1 for enhancing an audio signal by dividing it into sub-bands and temporarily removing some for efficiency. However, this claim specifically details that the enhancement process involves using a second, "reference" audio signal. This reference signal is also broken into sub-bands, with a corresponding set of bands removed. The remaining bands of the reference signal are then used to help an "echo compensation filter" remove echo from the primary audio signal's remaining sub-bands.

A search of the U.S. Court of Appeals for the Federal Circuit (CAFC) dockets for 2026 revealed no pending or recent litigation involving US Patent 8,320,575.

As of my analysis on April 26, 2026, there is one known litigation involving US Patent No. 8,320,575.

Cerence Operating Company v. Amazon.com, Inc. et al.

• Plaintiff(s): Cerence Operating Company
• Defendant(s): Amazon.com, Inc., Amazon.com Services LLC, and Amazon Web Services, Inc.
• Jurisdiction: U.S. District Court for the Eastern District of Texas
• Case Number: 2:26-cv-00372
• Filing Date: May 3, 2026 or May 4, 2026
• Outcome or Current Status: This is a very recent case. The complaint for patent infringement was filed on or around May 3, 2026. The docket shows the initial complaint and notice of filing have been entered. Simultaneously, Cerence filed a Section 337 complaint with the International Trade Commission (ITC) on May 5, 2026, seeking a limited exclusion order. The district court case is seeking monetary damages and injunctive relief. The case is in its earliest stages.

Proceedings overview

There are no AIA trial proceedings (Inter Partes Review, Post-Grant Review, or Covered Business Method review) on file for US Patent 8,320,575 according to both the USPTO Open Data Portal API and a comprehensive web search. This means the patent has not been subjected to PTAB challenges.

Strategic summary

As of today, May 29, 2026, all claims of US Patent 8,320,575 remain UNTESTED in AIA trial proceedings. There have been no PTAB challenges, meaning no claims have been canceled or sustained by the Board. Consequently, there is no estoppel landscape from PTAB proceedings that would bar future petitioners from raising any valid prior-art grounds. The absence of PTAB activity also means there are no discernible pattern signals regarding petitioner behavior or patent owner litigation strategy within the PTAB forum.

Recommended next steps

Since no PTAB activity exists for US Patent 8,320,575, a defendant facing assertion of this patent today has the full range of PTAB defenses available. This includes the option to file an Inter Partes Review (IPR) petition challenging the patentability of the claims based on prior art patents or printed publications under 35 U.S.C. §§ 102 and/or 103. The current litigation, Cerence Operating Company v. Amazon.com, Inc. et al. (E.D. Tex. Case No. 2:26-cv-00372), which was filed recently on May 3, 2026, along with a parallel ITC Section 337 complaint, indicates that the patent owner is actively asserting this patent. The lack of PTAB challenges for an actively asserted patent can sometimes signal that potential challengers have not yet mounted a defense or that the patent owner has historically settled quickly. However, it can also mean that prior art strong enough to meet the institution threshold for an IPR has not yet been identified or presented. Therefore, a thorough prior art search would be a critical next step to evaluate the viability of an IPR petition.

Inventors

• Gerhard Uwe Schmidt: Likely employed by Harman Becker Automotive Systems GmbH at the time of the invention and priority filing (EP07019281.0, 2007-10-01). Nuance Communications Inc. acquired the patent rights from Harman Becker, resulting in Nuance being listed as the original assignee on the US patent.
• Hans-Jörg Köpf: Likely employed by Harman Becker Automotive Systems GmbH at the time of the invention and priority filing (EP07019281.0, 2007-10-01).
• Günther Wirsching: Likely employed by Harman Becker Automotive Systems GmbH at the time of the invention and priority filing (EP07019281.0, 2007-10-01).

Original assignee

The original assignee listed on the issued patent is Nuance Communications Inc.. Nuance Communications Inc. was a major operating company specializing in speech recognition, natural language understanding, and artificial intelligence solutions. They shipped numerous products embodying such claims, particularly in the automotive, healthcare, and enterprise sectors. In 2022, Nuance Communications Inc. was acquired by Microsoft.

Assignment timeline

• 2009-05-01 (executed) / recorded 2010-01-19 — Reel 023810/0001

  • Conveyance: Assignment
  • Assignor: HARMAN BECKER AUTOMOTIVE SYSTEMS GMBH
  • Assignee: NUANCE COMMUNICATIONS, INC.
  • Correspondent: BARRY P. JOFFE - NUANCE COMMUNICATIONS, INC., 1 Burlington Woods Drive Burlington MA 01803
  • Context: Asset purchase agreement, transferring rights from original inventor's employer to Nuance.

• 2019-09-30 (executed) / recorded 2019-10-23 — Reel 050836/0191

  • Conveyance: Assignment
  • Assignor: NUANCE COMMUNICATIONS, INC.
  • Assignee: CERENCE INC.
  • Correspondent: CERENCE INC., 18 THIRD AVENUE BURLINGTON MA 01803. This correspondent recurs multiple times in this chain.
  • Context: Internal reorganization, transfer to a spin-off entity (Cerence).

• 2019-09-30 (executed) / recorded 2019-10-29 — Reel 050871/0001

  • Conveyance: Corrective Assignment
  • Assignor: NUANCE COMMUNICATIONS, INC.
  • Assignee: CERENCE OPERATING COMPANY
  • Correspondent: CERENCE INC., 18 THIRD AVENUE BURLINGTON MA 01803. This correspondent recurs multiple times in this chain.
  • Context: Corrective assignment to refine the assignee name from Cerence Inc. to Cerence Operating Company.

• 2019-10-01 (executed) / recorded 2019-11-07 — Reel 050953/0133

  • Conveyance: Security Agreement
  • Assignor: CERENCE OPERATING COMPANY
  • Assignee: BARCLAYS BANK PLC
  • Correspondent: CERENCE INC., 18 THIRD AVENUE BURLINGTON MA 01803. This correspondent recurs multiple times in this chain.
  • Context: Securitization of assets with a bank.

• 2020-06-12 (executed) / recorded 2020-06-12 — Reel 052927/0335

  • Conveyance: Release
  • Assignor: BARCLAYS BANK PLC
  • Assignee: CERENCE OPERATING COMPANY
  • Correspondent: CERENCE INC., 18 THIRD AVENUE BURLINGTON MA 01803. This correspondent recurs multiple times in this chain.
  • Context: Release of security interest by Barclays Bank PLC.

• 2020-06-12 (executed) / recorded 2020-06-15 — Reel 052935/0584

  • Conveyance: Security Agreement
  • Assignor: CERENCE OPERATING COMPANY
  • Assignee: WELLS FARGO BANK, N.A.
  • Correspondent: CERENCE INC., 18 THIRD AVENUE BURLINGTON MA 01803. This correspondent recurs multiple times in this chain.
  • Context: Securitization of assets with a new bank.

• 2019-09-30 (executed) / recorded 2022-04-19 — Reel 059804/0186

  • Conveyance: Corrective Assignment
  • Assignor: NUANCE COMMUNICATIONS, INC.
  • Assignee: CERENCE OPERATING COMPANY
  • Correspondent: CERENCE INC., 18 THIRD AVENUE BURLINGTON MA 01803. This correspondent recurs multiple times in this chain.
  • Context: Another corrective assignment, replacing a previous conveyance document to confirm the transfer from Nuance Communications to Cerence Operating Company.

• 2024-12-31 (executed) / recorded 2025-01-02 — Reel 069797/0818

  • Conveyance: Release
  • Assignor: WELLS FARGO BANK, NATIONAL ASSOCIATION
  • Assignee: CERENCE OPERATING COMPANY
  • Correspondent: CERENCE INC., 18 THIRD AVENUE BURLINGTON MA 01803. This correspondent recurs multiple times in this chain.
  • Context: Release of security interest by Wells Fargo Bank, National Association.

Timeline diagram

timeline
    title Ownership of US 8320575
    2008 : Filed by Nuance Comm
    2010 : Assigned to Nuance Comm
    2012 : Issued to Nuance Comm
    2019 : Assigned to Cerence Inc
         : To Cerence Operating Co (Corrective)
         : Security to Barclays Bank
    2020 : Release from Barclays Bank
         : Security to Wells Fargo
    2022 : To Cerence Operating Co (Corrective)
    2025 : Release from Wells Fargo
    2026 : Infringement suit filed

NPE / troll-pattern signals

1. Shell-entity transfer — Not present. All assignees in the chain (Harman Becker, Nuance, Cerence Inc., Cerence Operating Company) are operating companies. The transfers primarily represent asset acquisitions, corporate spin-offs, or financial security agreements.
2. Known asserter in the chain — Not present. Nuance Communications Inc. and Cerence Operating Company are known operating companies, not listed as prominent NPEs by RPX or Unified Patents.
3. Repeat correspondent across the chain — Present. The correspondent "CERENCE INC., 18 THIRD AVENUE BURLINGTON MA 01803" appears on records Reel 050836/0191, 050871/0001, 050953/0133, 052927/0335, 052935/0584, 059804/0186, and 069797/0818. This indicates consistent in-house legal handling for Cerence-related transfers and agreements.
4. Cascading transfers — Unclear. There are multiple transfers involving Cerence Inc. and Cerence Operating Company within a short period (October 2019). However, these appear to be related to a corporate spin-off and subsequent corrective assignments to clarify the entity name, along with concurrent security agreements, rather than successive sales through different shell entities. Reel 050836/0191, Reel 050871/0001, Reel 050953/0133 all occurred within a month and a half.
5. Pre-litigation transfer — Not present. The most recent assignment (release from Wells Fargo) occurred in January 2025. The first infringement suit was filed in May 2026, which is more than six months later.
6. Bankruptcy fire-sale — Not present. There is no indication that any of the assignors were undergoing bankruptcy proceedings at the time of transfer.
7. Privateering — Not present. Cerence Operating Company is an operating company asserting the patent itself.
8. Defensive aggregator (anti-NPE) — Not present. The chain does not terminate with a defensive aggregator.

Verdict

Operating-company assertion The assignment chain shows transfers between established operating companies (Harman Becker to Nuance, then Nuance to Cerence as part of a spin-off). The security agreements and releases are typical of corporate financing, and the repeated correspondent points to in-house legal handling by Cerence. Cerence Operating Company, an operating company, is the current assignee and has filed an infringement suit against Amazon.com, Inc. et al..

USPTO Assignment Center search for US8320575: https://assignmentcenter.uspto.gov/patents/8320575

Analysis of Relevant Prior Art for US Patent 8,320,575

The following analysis details the most relevant prior art cited during the prosecution of US Patent 8,320,575. For a reference to anticipate a claim under 35 U.S.C. § 102, it must disclose, either expressly or inherently, every element of that claim. The analysis below focuses on potential anticipation of the independent claims, particularly claim 1 and claim 10, which form the broadest basis of the invention. The filing date for US 8,320,575 is September 30, 2008, with a priority date of October 1, 2007. Any prior art must predate this priority date.

---

1. US Patent 5,272,695 A: "Subband echo canceller with adjustable coefficients using a series of step sizes"

• Full Citation: US Patent 5,272,695 A, filed by Nippon Telegraph And Telephone Corporation.
• Publication/Filing Date: Filed September 14, 1990; Published December 21, 1993.
• Brief Description: This patent describes an echo canceller that operates in the sub-band domain. An input signal is divided into multiple frequency sub-band signals by a filter bank. Adaptive filters then process these sub-band signals to cancel echo. The coefficients of these filters are updated using an algorithm that adjusts the step size for adaptation, aiming to improve convergence speed and reduce misadjustment. The processed sub-band signals are then synthesized back into a full-band signal.
• Potential Anticipation of Claims:
  • Claim 1: This reference appears to disclose several key elements of claim 1. It teaches dividing an audio signal into audio sub-band signals and processing a...subset of the audio sub-band signals (in this case, for echo cancellation). It also describes synthesizing the processed sub-band signals back into an enhanced audio signal. However, US 5,272,695 does not appear to explicitly teach the step of "excising a subset of the audio sub-band signals" for computational efficiency and then later "reconstructing at least a portion of the subset...that were excised." The '695 patent processes all the sub-bands generated by its filter bank. Therefore, it does not fully anticipate claim 1.
  • Claim 10: This reference is highly relevant as it deals with echo cancellation using a reference signal (the far-end signal that causes the echo). It discloses dividing both the primary (microphone) and reference signals into sub-bands and using the reference sub-bands to adapt an echo compensation filter. However, for the same reason it does not anticipate claim 1, it fails to anticipate claim 10. It lacks the specific steps of excising and then reconstructing a subset of sub-band signals for either the primary or the reference signal.

---

2. US Patent Application Publication 2009/0119096 A1: "Partial speech reconstruction"

• Full Citation: US Patent Application Publication 2009/0119096 A1, invented by Franz Gerl.
• Publication/Filing Date: Filed October 29, 2007; Published May 7, 2009.
• Brief Description: This application describes a method for processing a speech signal where the signal is converted into a spectral representation (frequency sub-bands). To reduce computational complexity, only a subset of these spectral components is transmitted or processed. The missing spectral components are then reconstructed at the receiving end by interpolating or extrapolating from the components that were processed. This is aimed at applications like speech coding and recognition where bandwidth or processing power is limited.
• Potential Anticipation of Claims:
  • Claim 1: This reference discloses the core concepts of processing a signal in sub-bands, discarding (or not processing) a portion of them, and then reconstructing the missing parts. It teaches converting a signal into spectral components (dividing), processing only a part of the spectrum (excising a subset, implicitly), and reconstructing the missing components. The final step of synthesizing them into a full-band signal is also inherent. This publication is highly relevant and could be argued to anticipate the key steps of claim 1, as the motivation (reducing computational load) and the general method (excising and reconstructing) are similar.
  • Claim 10: While US 2009/0119096 A1 teaches the general process of claim 1, it does not specifically describe using this method in the context of echo cancellation with a reference signal. It does not mention dividing a reference signal into sub-bands, excising corresponding sub-bands, and using the remainder to adapt an echo compensation filter. Therefore, it does not anticipate the specific combination of elements in claim 10.

---

3. US Patent 6,898,235 B1: "Wideband communication intercept and direction finding device using hyperchannelization"

• Full Citation: US Patent 6,898,235 B1, assigned to Argon St Incorporated.
• Publication/Filing Date: Filed December 10, 1999; Published May 24, 2005.
• Brief Description: This patent details a method for processing wideband signals by dividing them into a large number of narrow sub-bands (hyperchannelization). A key feature is the ability to process only a selected subset of these channels, which can be chosen based on signal activity or other criteria. This reduces the overall computational load required for signal analysis. The patent mentions that the selected channels can be processed for tasks like direction finding.
• Potential Anticipation of Claims:
  • Claim 1: This patent teaches dividing a signal into sub-bands and excising a subset by selecting only certain channels for further processing. The motivation is explicitly to reduce computational load. It also mentions that the processed signals can be used to create an output. However, it does not explicitly teach the step of reconstructing the excised sub-band signals to form a complete, enhanced full-band audio signal. The focus is on analyzing the selected bands rather than recreating a full-fidelity version of the original signal. Therefore, it does not fully anticipate claim 1.
  • Claim 10: This patent is not directed at echo cancellation and does not disclose the use of a reference signal as described in claim 10. Thus, it does not anticipate this claim.

---

4. US Patent Application Publication 2008/0140396 A1: "Model-based signal enhancement system"

• Full Citation: US Patent Application Publication 2008/0140396 A1, invented by Dominik Grosse-Schulte.
• Publication/Filing Date: Filed October 31, 2006; Published June 12, 2008.
• Brief Description: This publication describes a system for enhancing speech signals by separating them from noise. The signal is transformed into the frequency domain (sub-bands). A model of the speech signal is used to identify and preserve speech components while suppressing noise. The system can operate on selected frequency bands to improve efficiency.
• Potential Anticipation of Claims:
  • Claim 1: This reference teaches signal enhancement in the sub-band domain. It discloses dividing the signal and processing the sub-bands. It mentions that processing can be focused on selected bands, which implies the concept of excising others. However, similar to the other references, the explicit step of reconstructing the excised bands by interpolating or averaging from the processed bands, followed by synthesis, is not clearly taught. The focus is on noise suppression in the retained bands. Thus, it does not fully anticipate claim 1.
  • Claim 10: This reference is focused on noise reduction, not echo cancellation involving a reference signal in the manner specified by claim 10. Therefore, it does not anticipate this claim.

Obviousness Analysis of US Patent 8,320,575 under 35 U.S.C. § 103

This analysis examines the obviousness of the independent claims of US Patent 8,320,575 in light of prior art available before its priority date of October 1, 2007. A claim is considered obvious if the differences between the claimed invention and the prior art are such that the subject matter as a whole would have been obvious to a Person Having Ordinary Skill in the Art (PHOSITA).

A PHOSITA in the field of audio signal processing circa 2007 would typically have a master's degree in electrical engineering or a related field, along with several years of experience in digital signal processing (DSP), particularly in audio applications like echo cancellation and noise suppression. Such a person would be familiar with frequency-domain processing techniques like the Fast Fourier Transform (FFT), filter banks, and the trade-offs between computational complexity and signal quality.

---

Analysis of Independent Claim 1

Claim 1: A method for audio signal processing, comprising:

1. dividing an audio signal into audio sub-band signals;
2. excising a subset of the audio sub-band signals;
3. processing a remaining subset of the audio sub-band signals to obtain enhanced audio sub-band signals;
4. reconstructing at least a portion of the subset of the audio sub-band signals that were excised; and
5. synthesizing the enhanced audio sub-band signals with the reconstructed audio sub-band signals to form an enhanced audio signal.

Proposed Obviousness Combination:
The teachings of US5272695A (hereafter '695) in view of US20070071277A1 (hereafter '277) and the general knowledge of a PHOSITA regarding computational efficiency would have rendered Claim 1 obvious.

Reasoning:

1. Motivation to Combine:
   A PHOSITA is constantly driven to reduce the computational complexity and memory requirements of DSP algorithms to enable their use in real-time, low-power applications like hands-free car kits or mobile phones. The method of processing signals in the sub-band (frequency) domain was a well-established technique for this purpose. The '695 patent teaches a sub-band echo canceller, a computationally intensive application. A PHOSITA, when implementing such a system, would be motivated to find further efficiencies. It would have been obvious to consider processing only a subset of the sub-bands if doing so would significantly reduce the computational load without unacceptably degrading the audio quality. The idea of discarding less critical information to improve processing speed is a fundamental trade-off in computer science and signal processing.

2. Mapping of Prior Art to Claim Elements:

   • "dividing an audio signal into audio sub-band signals": This is explicitly taught by '695 in the context of echo cancellation. The abstract of '695 states its method involves a "subband echo canceller" which inherently requires dividing the signal into sub-bands. This is a foundational step in sub-band processing.

   • "excising a subset of the audio sub-band signals" and "processing a remaining subset": The '695 patent teaches processing the sub-band signals to perform echo cancellation. While it does not explicitly teach excising sub-bands to be reconstructed later, the motivation to do so is high for a PHOSITA seeking efficiency. The '277 patent application, in the context of watermarking, teaches modifying only selected sub-bands. For instance, '277 states, "For each sub-band, a decision is made whether to embed a watermark bit or not" (para.). This demonstrates the principle of selectively processing a subset of sub-bands while leaving others unprocessed or processed differently. A PHOSITA would readily understand that forgoing processing on some bands (i.e., "excising" them from the main processing path) would save MIPS (Millions of Instructions Per Second) and memory.

   • "reconstructing at least a portion of the subset of the audio sub-band signals that were excised": The concept of reconstructing or interpolating missing data is a standard technique in signal processing. The '277 patent application teaches the synthesis of a full-band signal from modified and unmodified sub-bands, which is analogous to reconstruction. More specifically, a PHOSITA would know that if, for example, every other frequency bin (sub-band) were discarded, the missing bins could be estimated by interpolating between the adjacent, processed bins. This is a common method for data reconstruction. The '575 patent itself describes this as a form of interpolation (Column 8, lines 16-24). Such interpolation techniques were well within the common general knowledge of a PHOSITA at the time.

   • "synthesizing the enhanced... and reconstructed... signals to form an enhanced audio signal": This final step is the necessary conclusion to any sub-band processing scheme. Both '695 and '277 teach the use of a synthesis filter bank to combine the processed sub-bands back into a single time-domain signal. It is the inverse operation of the initial "dividing" step.

Therefore, a PHOSITA starting with a standard sub-band processing system like that in '695 would have been motivated by the perpetual need for efficiency to selectively process only a subset of the sub-bands (as suggested by the principle in '277) and then reconstruct the unprocessed bands using standard interpolation techniques, thus arriving at the method of Claim 1.

---

Analysis of Independent Claim 10

Claim 10: A method for audio signal processing, comprising the steps of Claim 1, wherein the act of processing comprises:

• dividing a reference signal into reference sub-band signals;
• excising a subset of the reference sub-band signals that is equal in number to the excised subset of the audio sub-band signals;
• adapting filter coefficients of an echo compensation filter based on a remaining subset of the reference sub-band signals; and
• using the adapted filter coefficients to remove echo components from at least a portion of the remaining subset of the audio sub-band signals.

Proposed Obviousness Combination:
The teachings of US5272695A ('695) alone or in view of the same efficiency motivations discussed for Claim 1 would have rendered Claim 10 obvious.

Reasoning:

The '695 patent is titled "Subband echo canceller." The entire purpose of the patent is to describe an apparatus and method for echo cancellation in the sub-band domain. An echo canceller, by its very definition, operates by:

1. Receiving a primary audio signal (e.g., from a microphone) that contains an echo.
2. Receiving a "reference signal" (e.g., the far-end speaker signal being played out of a local loudspeaker) which is the source of the echo.
3. Using an adaptive filter to model the echo path and subtract an estimated echo from the primary signal.

The '695 patent explicitly teaches these steps in the sub-band domain.

1. Mapping of Prior Art to Claim Elements:

   • "dividing a reference signal into reference sub-band signals": This is inherent and necessary for the sub-band echo canceller in '695. To perform echo cancellation in the sub-band domain, both the microphone signal and the reference loudspeaker signal must be transformed into the same sub-bands to be compared and processed.

   • "excising a subset of the reference sub-band signals that is equal in number to the excised subset of the audio sub-band signals": This is an obvious and necessary consequence of the primary inventive concept of excising sub-bands for efficiency. If the processor is not going to enhance a particular sub-band of the microphone signal (because it has been "excised"), then there is no reason to process the corresponding sub-band of the reference signal for that purpose. A PHOSITA would immediately understand that to maintain correspondence, the same sub-bands must be ignored for both signals. Processing reference sub-bands that correspond to excised audio sub-bands would be useless and would defeat the entire purpose of the efficiency gain.

   • "adapting filter coefficients of an echo compensation filter based on a remaining subset of the reference sub-band signals" and "using the adapted filter coefficients to remove echo components from ... the remaining subset of the audio sub-band signals": This is the central teaching of '695. The patent describes adapting the filter coefficients for each sub-band based on the reference signal for that sub-band, and then using that filter to cancel the echo. Applying this known method only to the "remaining" (non-excised) sub-bands is a direct and obvious application of the efficiency concept.

In conclusion, Claim 10 merely recites a known sub-band echo cancellation architecture ('695) and applies to it the obvious efficiency-improving technique of skipping the processing for a subset of the sub-bands and reconstructing them later. The additional steps recited in Claim 10 are simply the necessary and logical consequences of applying the method of Claim 1 to the specific, well-known application of sub-band echo cancellation.

Detailed Analysis of U.S. Patent 8,320,575

Patent Term Adjustments (PTA) and Extensions (PTE):

A review of the prosecution history of U.S. Patent 8,320,575 on the USPTO's Patent Center portal indicates an adjusted expiration date of April 14, 2031. For utility patents filed after June 8, 1995, the term is typically 20 years from the earliest non-provisional filing date. In this case, the application was filed on September 30, 2008, which would normally result in an expiration date of September 30, 2028. The adjusted date suggests a significant Patent Term Adjustment (PTA) was granted by the USPTO to compensate for delays during the patent prosecution process. There is no indication of any Patent Term Extension (PTE), which is typically granted for delays caused by regulatory review and is distinct from PTA.

Continuation and Divisional Applications:

U.S. Patent 8,320,575 is the parent application to a divisional application, U.S. Patent 9,203,972. A divisional application is filed when the patent office determines that the original application contains more than one distinct invention. This allows the applicant to pursue claims to the non-elected invention in a separate application while retaining the priority date of the original "parent" application.

There are no continuation or continuation-in-part applications directly related to U.S. Patent 8,320,575.

Patent Family and Projected Expiration:

The patent family for U.S. Patent 8,320,575 includes its European counterpart, EP2045801B1, and the aforementioned U.S. divisional patent. The priority date for this family is October 1, 2007, based on the filing of the initial European patent application, EP07019281.

The projected expiration date for U.S. Patent 8,320,575, taking into account the granted Patent Term Adjustment, is April 14, 2031. This date is published on official patent data sources. It's important to note that the enforceability of a patent is also contingent upon the timely payment of maintenance fees, which are due at 3.5, 7.5, and 11.5 years from the issue date. A review of the USPTO's fee payment records confirms that all required maintenance fees for this patent have been paid to date.

Defensive Disclosure and Prior Art Derivations for US 8,320,575

Publication Date: May 8, 2026
Subject: Derivatives and extensions of methods for efficient audio signal processing in the sub-band regime. This document is intended to enter the public domain and serve as prior art for future inventions in this field.

---

Derivatives of Core Method (Claim 1)

The core method involves dividing an audio signal into sub-bands, excising a subset for computational efficiency, processing the remaining subset, reconstructing the excised subset, and synthesizing a final enhanced signal. The following are derivative works based on this core concept.

Axis 1: Component & Algorithm Substitution

Derivative 1.1: Wavelet Packet Decomposition for Non-Uniform Sub-Bands

• Enabling Description: Instead of using uniform-bandwidth filter banks like DFT or FFT, the initial "dividing" step is performed using a Wavelet Packet Decomposition (WPD). This allows for a non-uniform division of the frequency spectrum, providing higher frequency resolution at lower frequencies and higher temporal resolution at higher frequencies, which better matches human auditory perception. A 5-level WPD with a Daubechies 8 (db8) mother wavelet is used to decompose the signal. The "excising" step then selectively prunes entire branches of the wavelet packet tree based on a perceptual entropy calculation, discarding sub-bands with minimal contribution to speech intelligibility. Reconstruction of the pruned branches is achieved using polyphase interpolation from adjacent parent and child nodes in the tree before the inverse WPD synthesis.
• Mermaid.js Diagram:

  graph TD
      A[Audio Input y(n)] --> B{Wavelet Packet Decomposition};
      B --> C1[Sub-band 1];
      B --> C2[Sub-band 2];
      B --> C...[...];
      B --> CN[Sub-band N];
      subgraph Excision
          C1 --> D1{Process};
          C2 --> E2[Excise];
          C... --> D...{Process};
          CN --> EN[Excise];
      end
      subgraph Processing & Reconstruction
          D1 --> F1[Enhanced Sub-band 1];
          D... --> F...[Enhanced Sub-band ...];
          F1 & F... --> G{Reconstruct Excised Bands};
          G --> H1[Reconstructed Sub-band 2];
          G --> HN[Reconstructed Sub-band N];
      end
      F1 & F... & H1 & HN --> I{Inverse Wavelet Packet Synthesis};
      I --> J[Enhanced Output s(n)];
  

Derivative 1.2: Neural Network-Based Spectral Reconstruction

• Enabling Description: After excising a subset of sub-bands (e.g., every odd-indexed frequency bin from an STFT), the remaining sub-bands are processed for noise reduction. The reconstruction of the excised bands is performed by a Generative Adversarial Network (GAN). The generator network is a lightweight convolutional neural network (CNN) that takes the processed, sparse sub-band vector as input and outputs a fully dense, reconstructed vector. The discriminator network is trained to distinguish between original, complete sub-band vectors and the generator's reconstructed vectors. This system learns the statistical relationships between frequency bands, allowing it to generate highly accurate reconstructions that preserve harmonic structures, significantly outperforming linear or spline interpolation. The model is trained on a large corpus of speech data, such as the LibriSpeech dataset.
• Mermaid.js Diagram:

  sequenceDiagram
      participant A as Audio Input
      participant B as STFT
      participant C as Exciser
      participant D as Processor
      participant G as GAN Reconstructor
      participant S as iSTFT
  
      A->>B: Process Frame
      B->>C: Full Spectrum
      C->>D: Remaining Bands (Even)
      C-->>G: Remaining Bands (Even)
      D->>G: Enhanced Bands (Even)
      G->>S: Reconstructed Full Spectrum
      S->>A: Enhanced Audio Frame
  

---

Axis 2: Operational Parameter Expansion

Derivative 2.1: Massively Parallel Processing for Volumetric Acoustic Imaging

• Enabling Description: The method is scaled to process data from a large-aperture spherical microphone array comprising 4096 individual MEMS microphones for real-time 3D acoustic imaging. The input is not a single audio signal but a 4096-channel data stream. The sub-band division is performed on a GPU using a batched CUDA-based FFT kernel. The excision is applied across both frequency and spatial domains; sub-bands corresponding to spatial sectors with energy below a dynamic threshold are excised to focus computation on active sound sources. Processing involves beamforming and dereverberation on the remaining sub-bands. Reconstruction uses a 4D spatio-spectral interpolation model. The system processes audio at 96kHz to resolve ultrasonic frequencies for detailed source localization, requiring a throughput in the teraflop range.
• Mermaid.js Diagram:

  graph LR
      subgraph Input Stage
          M1[Mic 1]
          M2[Mic 2]
          M...[Mic ...]
          M4096[Mic 4096]
      end
      subgraph GPU Processing Core
          A[Batched FFT]
          B[Spatio-Spectral Excision]
          C[Beamforming/Denoising]
          D[4D Interpolation/Reconstruction]
          E[Batched iFFT & Synthesis]
      end
      M1 -- Channel 1 --> A
      M4096 -- Channel 4096 --> A
      A --> B --> C --> D --> E
      E --> F[3D Acoustic Image Stream]
  

Derivative 2.2: Application in Infrasonic Geopolitical Monitoring

• Enabling Description: The method is applied to signals from the International Monitoring System (IMS), which uses infrasound arrays to detect nuclear detonations. These signals are extremely low frequency (0.01 Hz to 10 Hz) and recorded over continental distances. The raw signal from an array is divided into narrow sub-bands using a high-resolution FFT (e.g., 2^24 points). Sub-bands known to contain persistent microbarom noise from oceanic wave interactions are excised. The remaining bands are processed using adaptive filters to enhance transient events. Reconstruction is critical to avoid artifacts that could be misinterpreted as treaty violations. The processed and reconstructed signals are synthesized to provide a clear signal for event analysis and source triangulation.
• Mermaid.js Diagram:

  stateDiagram-v2
      [*] --> Receiving: IMS Array Data (0.01-10Hz)
      Receiving --> SubBandDivision: Long-window FFT
      SubBandDivision --> Excision: Remove Microbarom Bands
      Excision --> Processing: Enhance Transients
      Processing --> Reconstruction: Interpolate Excised Bands
      Reconstruction --> Synthesis: Inverse FFT
      Synthesis --> Analysis: Event Detection & Triangulation
      Analysis --> [*]
  

---

Axis 3: Cross-Domain Application

Derivative 3.1: Accelerated Magnetic Resonance Imaging (MRI) Scans

• Enabling Description: The method is applied to the raw k-space data acquired during an MRI scan. The k-space data, which is the 2D or 3D Fourier transform of the image, is treated as a signal. It is divided into sub-bands (regions of k-space). The "excising" step corresponds to a compressed sensing acquisition pattern, where peripheral, high-frequency k-space regions are deliberately under-sampled or skipped, drastically reducing scan time. The remaining acquired sub-bands (central k-space) are processed to correct for motion artifacts. The non-acquired, "excised" sub-bands are then reconstructed using an iterative algorithm (e.g., Total Variation minimization or a deep learning model) that leverages the sparsity of the underlying medical image. The full k-space is then synthesized via an inverse Fourier transform to produce the final diagnostic image.
• Mermaid.js Diagram:

  flowchart TD
      A[MRI RF Coil Signal] --> B{k-Space Acquisition};
      B -- Full Sampling --> C[Standard k-Space Data];
      B -- Compressed Sensing --> D[Sub-Sampled k-Space (Remaining Bands)];
      D --> E{Motion Correction};
      subgraph Image Reconstruction
          E --> F{Reconstruct Missing k-Space (Excised Bands)};
          F --> G[Full Reconstructed k-Space];
      end
      G --> H{Inverse Fourier Transform};
      H --> I[High-Resolution MR Image];
  

Derivative 3.2: High-Frequency Trading Data Compression and Analysis

• Enabling Description: A time-series of stock market order book data is treated as a signal. The signal is divided into sub-bands using a Short-Time Fourier Transform (STFT) to create a spectrogram of market activity. The high-frequency sub-bands, representing algorithmic noise trading and fleeting quote changes, are excised to reduce the dataset size and computational load for trend analysis. The remaining lower-frequency sub-bands, representing more significant market movements, are processed using a Long Short-Term Memory (LSTM) network to predict price trends. The excised bands are then statistically reconstructed to provide a complete, but denoised, data stream for back-testing and risk modeling before being synthesized back into a time-series.
• Mermaid.js Diagram:

  sequenceDiagram
      participant T as Tick Data Stream
      participant W as Windowing & STFT
      participant E as High-Frequency Exciser
      participant L as LSTM Trend Predictor
      participant R as Statistical Reconstructor
      participant S as Synthesis
  
      T->>W: Ingest Market Data
      W->>E: Market Spectrogram
      E->>L: Low-Frequency Bands
      L-->>L: Predict Trend
      E->>R: Low-Frequency Bands
      R->>S: Denoised Full Spectrogram
      S->>T: Filtered Data for Trading Algo
  

---

Axis 4: Integration with Emerging Tech

Derivative 4.1: AI-Driven Adaptive Excision for Voice Assistants

• Enabling Description: The method is integrated into the audio front-end of a smart speaker. A reinforcement learning (RL) agent dynamically controls the excision process. The agent’s state is defined by real-time acoustic parameters: Signal-to-Noise Ratio (SNR), presence of a keyword (e.g., "Alexa"), and number of active speakers. The agent's action is to select an excision pattern (e.g., excise 25%, 50%, or 75% of sub-bands) and a reconstruction algorithm (linear, spline, or neural). The reward function is R = w1 * (CPU_savings) - w2 * (1 - WER), where WER is the Word Error Rate from the downstream speech recognizer. This allows the device to conserve maximum power during idle listening but instantly allocate full processing fidelity when a keyword is detected, optimizing the trade-off between power consumption and recognition accuracy.
• Mermaid.js Diagram:

  graph TD
      A[Mic Audio] --> B{Feature Extraction};
      B --> C[State: SNR, Keyword, etc.];
      C --> D[RL Agent (Policy Network)];
      D -- Action: Excision % --> E{Sub-band Excision};
      A --> F{Divide into Sub-bands};
      F --> E;
      E --> G{Enhancement Processing};
      G --> H{Reconstruction};
      D -- Action: Recon. Algo --> H;
      H --> I{Synthesis};
      I --> J{ASR Engine};
      J -- Word Error Rate --> K{Reward Calculation};
      C --> K;
      K -- Reward --> D;
  

Derivative 4.2: IoT-Edge Data Reduction with Blockchain Anchoring

• Enabling Description: In an industrial predictive maintenance system, a vibration sensor on a machine generates a continuous data stream. An edge computing device applies the '575 method. It divides the vibration signal into sub-bands. A pre-trained anomaly detection model identifies which sub-bands are exhibiting nominal behavior; these are excised. The remaining sub-bands, which may contain early fault signatures, are processed and transmitted to a cloud server. To ensure data integrity, a cryptographic hash of the remaining sub-band data, along with a bitmask representing the excision pattern, is computed and anchored to a private blockchain. This creates an immutable, auditable record of the sensor data, preventing tampering while reducing data transmission and storage costs by over 90%. The full signal can be reconstructed in the cloud for detailed analysis if a fault is confirmed.
• Mermaid.js Diagram:

  flowchart LR
      A[Vibration Sensor] --> B(Edge Device);
      subgraph B
          B1[Sub-band Division] --> B2{Anomaly Detection};
          B2 -- Nominal --> B3[Excise];
          B2 -- Anomaly --> B4[Process];
          B4 --> B5{Data Hashing};
          B3 & B4 --> B6[Assemble Payload];
      end
      B5 --> C((Blockchain Anchor));
      B6 --> D((Cloud Storage));
      D --> E{Reconstruction & Analysis};
  

---

Axis 5: The "Inverse" or Failure Mode

Derivative 5.1: Graceful Audio Degradation for Low-Power/High-CPU Load

• Enabling Description: The method is implemented in a mobile telecommunication device's baseband processor. A system monitor continuously tracks CPU load and battery state of charge. When the battery drops below 20% or CPU load exceeds 95%, the system triggers a "low-power" audio mode. In this mode, the excision ratio is increased from 50% (every other sub-band) to 75% (keep one, excise three). The processing block (e.g., echo canceller) reduces its filter tap length by half. The reconstruction algorithm switches from a computationally expensive spline interpolator to a simple zero-order hold. This results in audibly lower fidelity (more "robotic" sound) but prevents the call from dropping or audio from breaking up entirely, ensuring mission-critical functionality under adverse conditions.
• Mermaid.js Diagram:

  stateDiagram-v2
      state "Normal Mode" as Normal {
          [*] --> Processing
          Processing: Excision=50%, Full-tap filter, Spline recon.
          Processing --> Processing: CPU < 95% AND Battery > 20%
      }
      state "Low Power Mode" as LowPower {
          [*] --> Degraded
          Degraded: Excision=75%, Half-tap filter, Zero-order recon.
          Degraded --> Degraded: CPU > 95% OR Battery < 20%
      }
      Normal --> LowPower: CPU > 95% OR Battery < 20%
      LowPower --> Normal: CPU < 95% AND Battery > 20%
  

---

Combination Prior Art Scenarios

1. Combination with WebRTC Standard: The core method is implemented as a new module within the WebRTC audio processing pipeline. The RTCPeerConnection API is extended with a degradationPreference attribute. When a developer sets this to "maintain-framerate", the browser, upon detecting network congestion via RTCP receiver reports, will trigger the excision/reconstruction process on the audio stream before it is fed to the Opus encoder. The excision pattern is signaled to the remote peer via a custom RTP header extension, allowing the receiver to perform a more informed reconstruction, thus maintaining a smooth, uninterrupted conversation at the cost of temporary fidelity reduction.

2. Combination with GStreamer Open-Source Framework: A GStreamer plugin named subexcise is created. It acts as an audio filter element that can be dynamically inserted into any GStreamer pipeline. The element exposes properties such as excision-ratio (a float from 0.0 to 1.0) and mode (e.g., 'odd-even', 'random', 'perceptual'). A user could construct a pipeline for adaptive streaming: rtspsrc ! rtph264depay ! avdec_h264 ! videoconvert ! autovideosink pulsesrc ! audioconvert ! subexcise excision-ratio=0.5 ! opusenc ! rtpopuspay ! udpsink. The excision-ratio could be controlled in real-time by an application monitoring system resources.

3. Combination with SOFA (Spatially Oriented Format for Acoustics) Standard: The method is used to create a lossy, compressed variant of the SOFA file format, tentatively named SFC (SOFA-Compressed). A utility, sofa2sfc, takes a standard SOFA file containing high-resolution Head-Related Transfer Functions (HRTFs). For each HRTF, it performs a sub-band analysis, excises perceptually masked frequency bands, and stores only the remaining bands along with metadata for the reconstruction algorithm. This reduces the file size of complex spatial audio scenes by 70-80%, enabling their use in web-based and mobile applications where bandwidth and storage are at a premium. The reconstruction to a full SOFA-compliant structure happens at load time.