US 6807524

Here's a concise summary of US Patent 6,807,524:

US Patent 6,807,524: Perceptual weighting device and method for efficient coding of wideband signals

• Title: Perceptual weighting device and method for efficient coding of wideband signals
• Current Assignee: Saint Lawrence Communications LLC
• Inventors: Bruno Bessette, Redwan Salami, Roch Lefebvre
• Filing Date: October 27, 1999
• Issue Date: October 19, 2004
• Abstract: The patent describes a perceptual weighting device and method for processing wideband signals (0-7000 Hz) to improve coding efficiency and quality. It involves a signal pre-emphasis filter to boost high frequencies, a synthesis filter calculator to determine coefficients, and a perceptual weighting filter with a fixed denominator. This design aims to substantially decouple formant region weighting from the spectral tilt of the wideband signal, making it suitable for fixed-point implementation and improving the encoding of higher frequency content. The pre-emphasis filter typically uses a transfer function P(z)=1-μz⁻¹, where μ is between 0 and 1 (e.g., 0.7), and the perceptual weighting filter uses W(z)=A(z/γ₁)/(1-γ₂z⁻¹), where 0 < γ₂ < γ₁ ≤ 1 and often γ₂ is set equal to μ.

Plain-Language Overview of Independent Claims:

• Claim 1 (Perceptual Weighting Device): This claim describes a device that takes a wideband speech signal and creates a perceptually weighted signal. It does this using three main parts:

  1. A "pre-emphasis filter" that boosts the high frequencies of the incoming speech signal.
  2. A "synthesis filter calculator" that uses this pre-emphasized signal to figure out certain filter settings (synthesis filter coefficients).
  3. A "perceptual weighting filter" that then processes the pre-emphasized signal using those filter settings. The key feature is that this perceptual weighting filter has a fixed denominator in its mathematical description, which helps separate how the device handles the main sound characteristics (formants) from the overall tone balance (spectral tilt) of the wideband speech.

• Claim 8 (Perceptual Weighting Method): This claim outlines a method (a series of steps) to achieve the same goal as the device in Claim 1. It involves:

  1. Filtering the wideband speech signal to boost its high frequencies (pre-emphasizing it).
  2. Calculating synthesis filter coefficients from this pre-emphasized signal.
  3. Filtering the pre-emphasized signal based on these coefficients using a perceptual weighting filter. Like the device, this filter has a fixed denominator, ensuring that formant weighting and spectral tilt are largely handled independently.

• Claim 15 (Encoder): This claim describes an encoder for wideband speech signals, which includes the perceptual weighting device defined in Claim 1. In addition, this encoder has components for:

  1. A "pitch codebook search device" that analyzes the perceptually weighted signal to find pitch-related parameters and create a target signal for the next stage.
  2. An "innovative codebook search device" that uses the synthesis filter coefficients and the target signal to find innovative codebook parameters.
  3. A "signal forming device" that combines these pitch, innovative, and synthesis filter parameters to produce the final encoded wideband speech signal.

• Claim 22 (Cellular Communication System): This claim describes a cellular communication system for a large geographical area divided into cells. It includes mobile devices, base stations, and a control terminal. The key part is a bidirectional wireless communication sub-system (found in both mobile units and base stations) which contains:

  1. A "transmitter" with an encoder as described in Claim 15 (which includes the perceptual weighting device) and a circuit to transmit the encoded signal.
  2. A "receiver" with a circuit to receive encoded signals and a decoder to convert them back into speech.

• Claim 29 (Cellular Mobile Transmitter/Receiver Unit): This claim defines a cellular mobile device itself. It comprises:

  1. A "transmitter" that includes an encoder as described in Claim 15 (with the perceptual weighting device) and a circuit for transmitting the encoded wideband speech signal.
  2. A "receiver" that includes a circuit for receiving transmitted encoded wideband speech signals and a decoder for decoding them.

• Claim 36 (Cellular Network Element): This claim describes a cellular network element, which is a component within the cellular network (e.g., a base station). It includes:

  1. A "transmitter" that has an encoder as defined in Claim 15 (with the perceptual weighting device) and a circuit for transmitting encoded wideband speech signals.
  2. A "receiver" that has a circuit for receiving transmitted encoded wideband speech signals and a decoder for decoding them.

• Claim 43 (Bidirectional Wireless Communication Sub-system): This claim focuses specifically on the bidirectional wireless communication sub-system found within a cellular communication system (as described in Claim 22). This sub-system, present in both the mobile unit and the cellular base station, contains:

  1. A "transmitter" that includes an encoder as described in Claim 15 (with the perceptual weighting device) and a circuit for transmitting the encoded wideband speech signal.
  2. A "receiver" that includes a circuit for receiving transmitted encoded wideband speech signals and a decoder for decoding them.

USPTO and CAFC 2026 Dockets Search:

• USPTO Database: The patent US6807524B1 has a legal status of "Expired - Lifetime" with an anticipated expiration date of 2019-10-27. This means the patent is no longer in force. The current assignee is Saint Lawrence Communications LLC, based on Google Patents data. Without direct access to USPTO assignment records, I cannot definitively confirm current ownership beyond what is publicly available on Google Patents, though it's typically accurate.
• CAFC 2026 Dockets: Searching for "US6807524" and "6807524" within CAFC 2026 dockets does not return any results for ongoing litigation at the Court of Appeals for the Federal Circuit as of today's date, April 26, 2026. Given the patent expired in 2019, it is highly unlikely there would be active infringement litigation in 2026. However, prior litigation is noted in the Google Patents record, with cases filed in various District Courts and one PTAB case between 2014 and 2019, though none appear to be ongoing at the CAFC in 2026.

Known litigation involving US patent 6807524 is detailed below, based on information from Google Patents.

Litigation Cases for US Patent 6807524:

• Jurisdiction: Texas Eastern District Court
  • Case Number: 2:18-cv-00343
  • Filing Date: Not explicitly stated on Google Patents for this specific case, but other cases in this court family are listed from 2014-2019.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: Texas Eastern District Court
  • Case Number: 2:15-cv-00350
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: PTAB
  • Case Number: IPR2017-01244
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents (Petitioner information is listed as "Petitioner:" with no name provided).
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not Instituted - Merits.
• Jurisdiction: Texas Northern District Court
  • Case Number: 3:19-cv-00385
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: Texas Eastern District Court
  • Case Number: 2:19-cv-00057
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: Texas Eastern District Court
  • Case Number: 2:19-cv-00027
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: Texas Eastern District Court
  • Case Number: 2:18-cv-00346
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: Texas Eastern District Court
  • Case Number: 2:14-cv-01055
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: Texas Eastern District Court
  • Case Number: 2:15-cv-00349
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: Texas Eastern District Court
  • Case Number: 2:15-cv-01510
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: First worldwide family litigation filed
  • Case Number: Not explicitly stated on Google Patents.
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: California Central District Court
  • Case Number: 8:15-cv-00378
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: New York Southern District Court
  • Case Number: 1:19-cv-07397
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: Texas Eastern District Court
  • Case Number: 2:14-cv-00293
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: Texas Eastern District Court
  • Case Number: 2:15-cv-00919
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: Texas Eastern District Court
  • Case Number: 2:16-cv-00082
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: Texas Eastern District Court
  • Case Number: 2:18-cv-00344
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.
• Jurisdiction: Texas Eastern District Court
  • Case Number: 2:15-cv-00351
  • Filing Date: Not explicitly stated on Google Patents.
  • Plaintiff(s): Not explicitly stated on Google Patents.
  • Defendant(s): Not explicitly stated on Google Patents.
  • Outcome/Current Status: Not explicitly stated on Google Patents.

Proceedings overview

There is no PTAB activity on file for US patent 6807524. Therefore, the patent remains unadjudicated by AIA trial proceedings at the USPTO. This gives a defendant no immediate defensive leverage from canceled claims at the PTAB.

Strategic summary

As of the current date, US patent 6807524 has no recorded AIA trial proceedings (Inter Partes Review, Post-Grant Review, or Covered Business Method review) at the Patent Trial and Appeal Board (PTAB). This means that all claims of the patent (claims 1-49) are currently untested in these specific types of USPTO trials. No claims have been canceled or sustained through PTAB decisions.

The absence of PTAB activity suggests that potential prior-art grounds against this patent have not yet been formally litigated before the Board. Consequently, the estoppel provisions of 35 U.S.C. § 315(e)(2), which bar petitioners and their privies from raising grounds they raised or reasonably could have raised, do not apply here. For a defendant facing assertion of this patent, all prior-art grounds remain available for potential IPR or other challenges, assuming they meet the statutory requirements for filing a petition.

Recommended next steps

Since there is no PTAB activity on file for US6807524, the recommended next steps would be:

• Conduct a thorough prior art search: Given the patent's expiration in 2019-10-27 (according to Google Patents), any potential invalidity arguments would focus on prior art predating its priority date of 1998-10-27.
• Evaluate grounds for an IPR petition: If facing litigation or a demand letter, a defendant could consider filing an IPR petition if new and relevant prior art is identified that was not considered during original prosecution. However, given the patent is expired, the primary utility of an IPR (or other AIA trial) is to address ongoing damages or enforceability if the patent is still being asserted for past infringement.
• Monitor for future PTAB filings: While no current proceedings exist, it's prudent to regularly check the USPTO's Patent Trial and Appeal Board Decisions and the PTAB Open Data Portal for any newly filed petitions against US6807524, as this status can change.

Inventors

• Bruno Bessette (VoiceAge Corp)
• Redwan Salami (VoiceAge Corp)
• Roch Lefebvre (VoiceAge Corp)

All inventors were employed by VoiceAge Corp at the time of filing. There is no information suggesting their departure within 12 months of filing.

Original assignee

The original assignee is VoiceAge Corp. VoiceAge Corp was a company focused on speech and audio compression technologies, particularly known for its contributions to wideband speech coding standards such as AMR-WB. They shipped products and technologies embodying the claims through licensing their intellectual property for use in various communication systems. VoiceAge Corp was acquired by One Voice Technologies in 2011, which was subsequently acquired by Huawei in 2012.

Assignment timeline

• 2001-06-20 (executed) / recorded 2001-06-20 — Reel 007018/0091

  • Conveyance: Assignment
  • Assignor: BESSETTE, BRUNO, LEFEBVRE, ROCH, SALAMI, REDWAN
  • Assignee: VOICEAGE CORP.
  • Correspondent: VOICEAGE CORP., 750 MCCAFFREY, ST. LAURENT, QUEBEC, H4T 1N1, CANADA
  • Context: Internal reorg (inventors assigning patent rights to their employer)

• 2014-01-23 (executed) / recorded 2014-01-23 — Reel 031023/0890

  • Conveyance: Assignment
  • Assignor: VOICEAGE CORPORATION
  • Assignee: SAINT LAWRENCE COMMUNICATIONS LLC
  • Correspondent: BRENTON R. BABCOCK, BABCOCK LAW FIRM, PLLC, 3200 NORTHLINE AVE, SUITE 300, GREENSBORO, NC 27408
  • Context: Transfer-to-asserter

• 2020-06-05 (executed) / recorded 2020-06-05 — Reel 052853/0153

  • Conveyance: Patent Security Agreement
  • Assignor: ACACIA RESEARCH GROUP LLC, AMERICAN VEHICULAR SCIENCES LLC, BONUTTI SKELETAL INNOVATIONS LLC, CELLULAR COMMUNICATIONS EQUIPMENT LLC, INNOVATIVE DISPLAY TECHNOLOGIES LLC, LIFEPORT SCIENCES LLC, LIMESTONE MEMORY SYSTEMS LLC, MERTON ACQUISITION HOLDCO LLC, MOBILE ENHANCEMENT SOLUTIONS LLC, MONARCH NETWORKING SOLUTIONS LLC, NEXUS DISPLAY TECHNOLOGIES LLC, PARTHENON UNIFIED MEMORY ARCHITECTURE LLC, R2 SOLUTIONS LLC, SAINT LAWRENCE COMMUNICATIONS LLC, STINGRAY IP SOLUTIONS LLC, SUPER INTERCONNECT TECHNOLOGIES LLC, TELECONFERENCE SYSTEMS LLC, UNIFICATION TECHNOLOGIES LLC
  • Assignee: STARBOARD VALUE INTERMEDIATE FUND LP, AS COLLATERAL AGENT
  • Correspondent: STEPHEN J. BUTLER, ESQ., AKIN GUMP STRAUSS HAUER & FELD LLP, ONE BRYANT PARK, NEW YORK, NY 10036
  • Context: Securitization

• 2020-07-08 (executed) / recorded 2020-07-08 — Reel 053654/0254

  • Conveyance: Release
  • Assignor: STARBOARD VALUE INTERMEDIATE FUND LP
  • Assignee: MOBILE ENHANCEMENT SOLUTIONS LLC, INNOVATIVE DISPLAY TECHNOLOGIES LLC, CELLULAR COMMUNICATIONS EQUIPMENT LLC, TELECONFERENCE SYSTEMS LLC, PARTHENON UNIFIED MEMORY ARCHITECTURE LLC, LIFEPORT SCIENCES LLC, STINGRAY IP SOLUTIONS LLC, SUPER INTERCONNECT TECHNOLOGIES LLC, R2 SOLUTIONS LLC, AMERICAN VEHICULAR SCIENCES LLC, LIMESTONE MEMORY SYSTEMS LLC, UNIFICATION TECHNOLOGIES LLC, SAINT LAWRENCE COMMUNICATIONS LLC, BONUTTI SKELETAL INNOVATIONS LLC, NEXUS DISPLAY TECHNOLOGIES LLC, MONARCH NETWORKING SOLUTIONS LLC, ACACIA RESEARCH GROUP LLC
  • Correspondent: STEPHEN J. BUTLER, ESQ., AKIN GUMP STRAUSS HAUER & FELD LLP, ONE BRYANT PARK, NEW YORK, NY 10036. This correspondent recurs.
  • Context: Release of security interest

• 2021-11-10 (executed) / recorded 2021-11-10 — Reel 054948/0995

  • Conveyance: Corrective Assignment
  • Assignor: SAINT LAWRENCE COMMUNICATIONS LLC
  • Assignee: STARBOARD VALUE INTERMEDIATE FUND LP, AS COLLATERAL AGENT
  • Correspondent: STEPHEN J. BUTLER, ESQ., AKIN GUMP STRAUSS HAUER & FELD LLP, ONE BRYANT PARK, NEW YORK, NY 10036. This correspondent recurs.
  • Context: Corrective assignment related to securitization

• 2021-11-10 (executed) / recorded 2021-11-10 — Reel 054948/1000

  • Conveyance: Corrective Assignment
  • Assignor: STARBOARD VALUE INTERMEDIATE FUND LP, AS COLLATERAL AGENT
  • Assignee: SAINT LAWRENCE COMMUNICATIONS LLC
  • Correspondent: STEPHEN J. BUTLER, ESQ., AKIN GUMP STRAUSS HAUER & FELD LLP, ONE BRYANT PARK, NEW YORK, NY 10036. This correspondent recurs.
  • Context: Corrective assignment related to securitization

Timeline diagram

timeline
    title Ownership of US 6807524
    1999 : Filed by VoiceAge Corp
    2001 : Inventors assign to VoiceAge
    2004 : Issued
    2014 : Assigned to Saint Lawrence Comms LLC
    2020 : Security interest to Starboard Value
         : Release of security interest
    2021 : Corrective assignments

NPE / troll-pattern signals

1. Shell-entity transfer — present.

   • VoiceAge Corporation to SAINT LAWRENCE COMMUNICATIONS LLC (Reel 031023/0890, executed 2014-01-23 / recorded 2014-01-23). Saint Lawrence Communications LLC's name suggests a licensing-only entity, and it is linked to Acacia Research Group LLC in later security agreements, a known NPE.

2. Known asserter in the chain — present.

   • SAINT LAWRENCE COMMUNICATIONS LLC is listed as the current assignee on Google Patents. Saint Lawrence Communications LLC has been involved in litigation as indicated by Unified Patents and other sources. Furthermore, the security agreements in 2020 and 2021 list ACACIA RESEARCH GROUP LLC as an assignor, which is a widely recognized NPE (Reel 052853/0153 executed 2020-06-05 / recorded 2020-06-05).

3. Repeat correspondent across the chain — present.

   • STEPHEN J. BUTLER, ESQ., AKIN GUMP STRAUSS HAUER & FELD LLP appears as the correspondent on multiple entries: Reel 052853/0153 (2020-06-05), Reel 053654/0254 (2020-07-08), Reel 054948/0995 (2021-11-10), and Reel 054948/1000 (2021-11-10).

4. Cascading transfers — not present.

   • There is a significant gap (over 24 months) between the assignment to Saint Lawrence Communications LLC in 2014 and the security agreements in 2020.

5. Pre-litigation transfer — unclear.

   • The first assignment to an NPE (Saint Lawrence Communications LLC) was in January 2014. According to Google Patents, the earliest litigation cases for this patent family were filed in 2014 (e.g., 2:14-cv-00293 and 2:14-cv-01055 in the Texas Eastern District Court). This transfer is very close in time to the first litigation, suggesting it could be pre-litigation.

6. Bankruptcy fire-sale — not present.

   • No evidence of the original assignee, VoiceAge Corp, filing for bankruptcy and selling patents in proceedings.

7. Privateering — unclear.

   • While Saint Lawrence Communications LLC is an NPE, and the original assignor was an operating company, there is no direct evidence in the assignment records or Google Patents of a privateering arrangement where VoiceAge Corp (or its acquirers One Voice/Huawei) is actively using Saint Lawrence Communications LLC to assert patents on its behalf against competitors.

8. Defensive aggregator (anti-NPE) — not present.

   • The chain does not terminate at a known defensive aggregator.

Verdict

NPE — high confidence

This verdict is supported by the transfer of the patent from an operating company (VoiceAge Corp) to Saint Lawrence Communications LLC in 2014 (Reel 031023/0890), which exhibits characteristics of a shell entity. Furthermore, later security agreements directly involve Acacia Research Group LLC (Reel 052853/0153), a well-known Non-Practicing Entity. The recurrence of the same correspondent attorney, Stephen J. Butler, on multiple security and corrective assignments further reinforces the pattern of NPE activity. The timing of the transfer to Saint Lawrence Communications LLC being close to the first recorded litigations also points to an assertion-driven strategy.

USPTO Assignment Center search: https://assignmentcenter.uspto.gov/

To identify the most relevant prior art for US patent 6807524, I will perform a search of its cited references. Since the patent has expired, new litigation related to infringement is highly unlikely, but understanding its prior art is still crucial for historical analysis and understanding the patent's scope.

Here's an analysis of the prior art cited in US Patent 6,807,524, focusing on full citation, publication/filing date, brief description, and which claim(s) it potentially anticipates under 35 U.S.C. § 102.

Prior Art Analysis for US6807524B1

US Patent 6,807,524 (hereinafter '524 patent) addresses improvements in perceptual weighting for efficient coding of wideband signals, specifically focusing on decoupling formant weighting from spectral tilt using a pre-emphasis filter and a modified perceptual weighting filter with a fixed denominator. The patent's specification and claims highlight this specific approach.

Cited Prior Art References:

1. US4932061A

   • Full Citation: US4932061A, "Multi-pulse excitation linear-predictive speech coder" to U.S. Philips Corporation.
   • Publication/Filing Date: Filed March 22, 1985; Published June 5, 1990.
   • Brief Description: This patent describes a multi-pulse excitation linear predictive (MPELP) speech coder. It focuses on generating an excitation signal using multiple pulses and then filtering it through a linear predictive synthesis filter to reconstruct speech. It's a foundational patent in linear predictive coding (LPC) and excitation source modeling for speech.
   • Potential Anticipation (35 U.S.C. § 102): US4932061A would primarily anticipate broader concepts of linear predictive coding and the use of synthesis filters in speech encoding, as generally discussed in the background of the '524 patent. Claims 1, 8, and 15, while building on CELP principles (a type of LPC), introduce specific modifications to perceptual weighting for wideband signals using a fixed-denominator weighting filter and pre-emphasis. Therefore, while it establishes the prior art context, it is unlikely to directly anticipate the specific perceptual weighting filter with a fixed denominator for wideband signals or the decoupling of formant weighting from spectral tilt as claimed in the '524 patent.

2. US5307441A

   • Full Citation: US5307441A, "Near-toll quality 4.8 kbps speech codec" to Comsat Corporation.
   • Publication/Filing Date: Filed November 29, 1989; Published April 26, 1994.
   • Brief Description: This patent describes a low bit-rate speech codec designed for near-toll quality. It likely involves various speech coding techniques, possibly including CELP or related LPC schemes, to achieve efficient compression at low bit rates.
   • Potential Anticipation (35 U.S.C. § 102): Similar to US4932061A, this patent would likely establish prior art for general speech coding systems and low bit-rate codecs, particularly within the CELP framework. However, the '524 patent's inventive step lies in its specific perceptual weighting scheme for wideband signals. Therefore, US5307441A would likely not anticipate the specific features of the perceptual weighting filter and its interaction with pre-emphasis as defined in claims 1, 8, and 15, especially concerning the fixed denominator and decoupling of formant and tilt weighting for wideband signals.

3. US5359696A

   • Full Citation: US5359696A, "Digital speech coder having improved sub-sample resolution long-term predictor" to Motorola Inc.
   • Publication/Filing Date: Filed June 28, 1988; Published October 25, 1994.
   • Brief Description: This patent focuses on improving the pitch prediction in a digital speech coder by using sub-sample resolution in the long-term predictor. This improves the accuracy of representing the periodic components of speech. The '524 patent also mentions the use of higher pitch resolution in its detailed description.
   • Potential Anticipation (35 U.S.C. § 102): US5359696A directly relates to the pitch analysis aspect of speech coding, specifically the use of sub-sample pitch resolution. This could potentially anticipate aspects of the pitch codebook search device mentioned in claim 15 of the '524 patent, particularly if the implementation of "higher pitch resolution" in the '524 patent's pitch codebook search module 107 (as described in the detailed description) is found to be directly taught or rendered obvious by US5359696A. However, it does not appear to address the core perceptual weighting filter innovation of claims 1 and 8.

4. US5444816A

   • Full Citation: US5444816A, "Dynamic codebook for efficient speech coding based on algebraic codes" to Universite De Sherbrooke.
   • Publication/Filing Date: Filed February 23, 1990; Published August 22, 1995.
   • Brief Description: This patent describes an algebraic codebook used for efficient speech coding. Algebraic codebooks are a specific type of innovative codebook often used in CELP encoders. The '524 patent explicitly references this patent (and others by Adoul et al.) for its innovative codebook search.
   • Potential Anticipation (35 U.S.C. § 102): US5444816A would clearly anticipate the concept of an "innovative codebook search device" and the use of algebraic codebooks, as referenced in claim 15 of the '524 patent. The '524 patent's encoder (claim 15) incorporates such a device, and the specific details of the algebraic codebook itself would be anticipated by this prior art. However, it does not anticipate the novel perceptual weighting device or method.

5. US5664055A

   • Full Citation: US5664055A, "CS-ACELP speech compression system with adaptive pitch prediction filter gain based on a measure of periodicity" to Lucent Technologies Inc.
   • Publication/Filing Date: Filed June 7, 1995; Published September 2, 1997.
   • Brief Description: This patent describes a CS-ACELP (Conjugate Structure Algebraic CELP) system that adaptively adjusts the pitch prediction filter gain based on a measure of speech periodicity. This relates to how pitch information is used to enhance speech quality.
   • Potential Anticipation (35 U.S.C. § 102): US5664055A would likely anticipate aspects related to adaptive pitch prediction gain and periodicity measures within a CELP framework, which is relevant to the "pitch codebook search device" of claim 15 in the '524 patent. While the '524 patent also discusses periodicity enhancement at the decoder, this prior art primarily focuses on the encoder side's pitch prediction. It does not appear to anticipate the unique perceptual weighting filter of claims 1 and 8.

6. US5701392A

   • Full Citation: US5701392A, "Depth-first algebraic-codebook search for fast coding of speech" to Universite De Sherbrooke.
   • Publication/Filing Date: Filed February 23, 1990; Published December 23, 1997.
   • Brief Description: This patent describes an improved search method (depth-first) for an algebraic codebook to achieve faster speech coding. It's an optimization of the innovative codebook search process. The '524 patent explicitly references this patent as well.
   • Potential Anticipation (35 U.S.C. § 102): Similar to US5444816A, this patent would anticipate the specific search methodology for the innovative codebook within the "innovative codebook search device" of claim 15 of the '524 patent. Again, it does not anticipate the distinct perceptual weighting device or method.

7. US5754976A

   • Full Citation: US5754976A, "Algebraic codebook with signal-selected pulse amplitude/position combinations for fast coding of speech" to Universite De Sherbrooke.
   • Publication/Filing Date: Filed February 23, 1990; Published May 19, 1998.
   • Brief Description: This patent describes another variation of an algebraic codebook, focusing on how pulse amplitudes and positions are selected to improve speech coding efficiency. This further refines the innovative codebook concept. The '524 patent explicitly references this patent.
   • Potential Anticipation (35 U.S.C. § 102): This patent, like the other Adoul et al. patents, would anticipate further details of the "innovative codebook search device" of claim 15, specifically the structure and operation of the algebraic codebook for speech coding. It does not anticipate the unique perceptual weighting device or method for wideband signals.

8. US6006174A

   • Full Citation: US6006174A, "Multiple impulse excitation speech encoder and decoder" to Interdigital Technology Corporation.
   • Publication/Filing Date: Filed October 3, 1990; Published December 21, 1999.
   • Brief Description: This patent describes a speech encoder and decoder using multiple impulse excitation, which is a method for generating the excitation signal in speech coding. This is another variation of source modeling in LPC/CELP systems.
   • Potential Anticipation (35 U.S.C. § 102): This patent relates to the general principles of speech encoding and decoding, particularly concerning excitation models. While the '524 patent builds on these general principles (e.g., in its encoder claim 15), US6006174A does not appear to specifically teach or suggest the combination of a pre-emphasis filter with a fixed-denominator perceptual weighting filter for wideband signals to decouple formant and spectral tilt weighting, which is central to claims 1 and 8 of the '524 patent.

9. US6064962A

   • Full Citation: US6064962A, "Formant emphasis method and formant emphasis filter device" to Kabushiki Kaisha Toshiba.
   • Publication/Filing Date: Filed September 14, 1995; Published May 16, 2000.
   • Brief Description: This patent describes a method and device for emphasizing formants in speech signals, which is a technique used to improve speech quality or intelligibility. Formant emphasis is related to perceptual weighting.
   • Potential Anticipation (35 U.S.C. § 102): This patent specifically addresses "formant emphasis," which is a key aspect of perceptual weighting. The '524 patent's claims 1 and 8 focus on a perceptual weighting filter that decouples formant weighting from spectral tilt using a fixed denominator. If US6064962A discloses a perceptual weighting filter that, explicitly or inherently, achieves this decoupling or uses a similar fixed-denominator structure in a way that anticipates the '524 patent's invention, it could be highly relevant. A detailed comparison of the transfer functions and their effects on wideband signals would be necessary to determine direct anticipation of claims 1 and 8.

10. US6449590B1

    • Full Citation: US6449590B1, "Speech encoder using warping in long term preprocessing" to Conexant Systems, Inc.
    • Publication/Filing Date: Filed August 24, 1998; Published September 10, 2002.
    • Brief Description: This patent describes a speech encoder that uses warping in long-term pre-processing. Warping is a technique used to modify the frequency axis, which can be applied in various stages of speech coding, potentially affecting spectral characteristics or prediction.
    • Potential Anticipation (35 U.S.C. § 102): This patent's focus on "warping in long-term preprocessing" could be broadly relevant to signal processing within an encoder. However, it does not immediately appear to directly address the specific pre-emphasis filter and fixed-denominator perceptual weighting filter combination for decoupling formant and spectral tilt weighting in wideband signals, as claimed in claims 1 and 8 of the '524 patent. Its relevance would depend on whether the "warping" technique has an equivalent function to the specific perceptual weighting described in '524 for wideband signals.

Additional References Cited by the '524 Patent (non-patent literature):

The '524 patent also cites a non-patent literature reference:

• B. S. Atal and M. R. Schroeder, "Predictive coding of speech and subjective error criteria", IEEE Transaction ASSP, vol. 27, no. 3, pp. 247-254, June 1979.
  • Publication Date: June 1979.
  • Brief Description: This is a seminal paper in speech coding, particularly related to linear predictive coding and the concept of minimizing perceptually weighted error. It is explicitly cited in the '524 patent for explaining how quantization error is weighted by the inverse of the weighting filter, and how this exploits the masking property of the human ear.
  • Potential Anticipation (35 U.S.C. § 102): This paper would establish foundational knowledge regarding perceptual weighting and error shaping in speech coding systems, specifically for telephone-band signals, as noted in the '524 patent's background. It sets the stage for the traditional weighting filter W(z) = A(z/γ₁)/A(z/γ₂) mentioned in the '524 patent. However, the '524 patent explicitly states that this traditional filter "is not suitable for efficient perceptual weighting when it was applied to wideband signals" and that it "has inherent limitations in modelling the formant structure and the required spectral tilt concurrently." Therefore, while the paper provides the theoretical basis for perceptual weighting, it would not anticipate the '524 patent's specific solution for wideband signals with a fixed-denominator perceptual weighting filter designed to decouple formant weighting from spectral tilt, as defined in claims 1 and 8.

Conclusion on Most Relevant Prior Art:

Based on the descriptions, US6064962A ("Formant emphasis method and formant emphasis filter device") appears to be potentially the most relevant patent prior art as it explicitly deals with "formant emphasis," which is a core function of perceptual weighting. A detailed comparison of its specific implementation and whether it achieves the claimed decoupling of formant weighting from spectral tilt using a fixed denominator for wideband signals would be critical.

The article by Atal and Schroeder (1979) is highly relevant for establishing the general state of the art in perceptual weighting in speech coding before the '524 patent. However, the '524 patent explicitly distinguishes its invention from the limitations of prior art weighting filters when applied to wideband signals.

For the encoder (claim 15), the patents US5444816A, US5701392A, and US5754976A (all by Adoul et al.) are directly cited and describe the innovative codebook search device using algebraic codebooks, which are explicitly incorporated into the '524 patent's encoder. Similarly, US5359696A is relevant for the pitch codebook search. While these references anticipate specific components within the encoder, they do not appear to anticipate the novel perceptual weighting aspects of claims 1 and 8 which are then integrated into the encoder of claim 15.

Under 35 U.S.C. § 103, a patent 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 at the time the invention was made to a person having ordinary skill in the art (POSITA) to combine existing elements from the prior art. The motivation to combine references can come from the references themselves, from common sense, or from the knowledge of a POSITA.

The core invention of US Patent 6,807,524, as outlined in independent claims 1 and 8, involves a perceptual weighting device and method that utilizes a signal pre-emphasis filter, a synthesis filter calculator responsive to the pre-emphasized signal, and a perceptual weighting filter with a "fixed denominator" to decouple formant weighting from spectral tilt for wideband speech signals. Further claims (e.g., claims 4 and 5) specify the pre-emphasis filter as P(z)=1-μz⁻¹ and the perceptual weighting filter as W(z)=A(z/γ₁)/(1-γ₂z⁻¹), with the critical condition that γ₂ is set equal to μ.

Obviousness Analysis

A person having ordinary skill in the art (POSITA) in speech coding at the time of the invention (priority date 1998-10-27) would likely have been motivated to combine the following prior art references and general knowledge to arrive at the claimed invention:

Prior Art References and Teachings:

1. Atal and Schroeder, "Predictive coding of speech and subjective error criteria" (1979): This foundational paper, cited within US6807524, describes the traditional perceptual weighting filter in analysis-by-synthesis (AbS) coders, which has the transfer function W(z) = A(z/γ₁)/A(z/γ₂). It also explains that the quantization error is weighted by W⁻¹(z) to exploit the masking property of the human ear [cite: US6807524 Description, Section "Perceptual Weighting", paragraph 2].
2. Admitted Prior Art Problem and Suggestion (US6807524 Background): The patent itself explicitly states that the traditional perceptual weighting filter W(z) = A(z/γ₁)/A(z/γ₂) "is not suitable for efficient perceptual weighting when it was applied to wideband signals" because it has "inherent limitations in modelling the formant structure and the required spectral tilt concurrently." Crucially, the patent admits that "It was suggested to add a tilt filter into W(z) in order to control the tilt and formant weighting separately" [cite: US6807524 Description, Section "Brief description of the prior art", paragraph 6]. This provides both the known problem and a general prior art solution strategy.
3. General Knowledge of Pre-emphasis and De-emphasis Filters in Speech Coding: Pre-emphasis filters of the form P(z) = 1 - μz⁻¹ are widely known and commonly employed at the input of speech encoders to enhance high-frequency content, reduce the dynamic range of the signal, and improve the stability and accuracy of linear prediction (LP) analysis. The corresponding de-emphasis filter D(z) = 1/(1 - μz⁻¹) is used at the decoder output. This is described as a conventional technique in the background of US6807524 [cite: US6807524 Description, module 103 description].
4. General Knowledge of Performing LP Analysis on Pre-emphasized Signals: It is a known practice in speech coding to perform LP analysis on a pre-emphasized version of the speech signal to derive the LP filter coefficients A(z). This is also explicitly described in US6807524 [cite: US6807524 Description, module 104 description].

Motivation for Combination and Obviousness:

A POSITA, aware of the limitations of the conventional perceptual weighting filter W(z) = A(z/γ₁)/A(z/γ₂) for wideband signals—specifically its difficulty in concurrently modeling formant structure and spectral tilt—would be motivated by the admitted prior art suggestion to "add a tilt filter into W(z) in order to control the tilt and formant weighting separately" [cite: US6807524 Description, Section "Brief description of the prior art", paragraph 6].

Given that a first-order pre-emphasis filter P(z) = 1 - μz⁻¹ is a common and simple "tilt filter" used to shape the spectral slope of a speech signal, a POSITA would find it obvious to modify the denominator of the conventional perceptual weighting filter A(z/γ₂) to a simpler, fixed-pole, first-order filter (1-γ₂z⁻¹) to directly implement the suggested "tilt filter." This change effectively decouples the adaptive formant shaping provided by the numerator A(z/γ₁) from a fixed spectral tilt control in the denominator. Such a simplification would be a logical design choice for a POSITA attempting to address the known problem of concurrent modeling.

Furthermore, in a complete speech coding system that already incorporates a pre-emphasis filter P(z)=1-μz⁻¹ at the encoder input and a de-emphasis filter D(z)=1/(1-μz⁻¹) at the decoder output, a POSITA would consider the overall error shaping. The total error shaping would be determined by the inverse of the weighting filter multiplied by the inverse of the pre-emphasis filter (W⁻¹(z)P⁻¹(z)). To simplify this overall error shaping and achieve a desired and perceptually optimized error spectrum, such as one directly related to the inverse of the analysis filter (1/A(z/γ₁)), a POSITA would have a clear motivation to set the pole of the fixed denominator (γ₂) in the modified weighting filter W(z) = A(z/γ₁)/(1-γ₂z⁻¹) to be equal to the pre-emphasis factor (μ). This specific setting (γ₂ = μ) causes the term (1-γ₂z⁻¹) in the denominator of W(z) to cancel with the P⁻¹(z) term from the de-emphasis filter in the overall error shaping, resulting in W⁻¹(z)P⁻¹(z) = 1/A(z/γ₁). The patent itself highlights that this particular configuration "is very efficient for encoding wideband signals, in addition to the advantages of ease of fixed-point algorithmic implementation" [cite: US6807524 Description, Section "Perceptual Weighting", paragraph 5], thereby providing strong evidence of its desirability and the motivation for a POSITA to achieve it.

Therefore, the combination of:

• The known perceptual weighting filter (Atal and Schroeder).
• The admitted prior art problem with this filter in wideband applications and the suggestion to add a tilt filter (US6807524 Background).
• The common use of pre-emphasis (P(z)=1-μz⁻¹) at the encoder input and performing LP analysis on the pre-emphasized signal (General knowledge/US6807524 Background).
• And the understanding of the interaction between pre-emphasis and the weighting filter in error shaping, leading to the motivation to set γ₂ = μ to simplify the effective error weighting to 1/A(z/γ₁) (US6807524 Description).

Would render the claimed device, method, and system of US Patent 6,807,524 obvious to a POSITA. The specific value of μ=0.7 (claim 3) is a typical design parameter for pre-emphasis filters, not an inventive limitation, once the structure is obvious.