Case: 18-2382   Document: 45     Page: 1    Filed: 02/07/2020




   United States Court of Appeals
       for the Federal Circuit
                 ______________________

                      APPLE INC.,
                       Appellant

                            v.

      ANDREA ELECTRONICS CORPORATION,
                     Appellee
              ______________________

                  2018-2382, 2018-2383
                 ______________________

     Appeals from the United States Patent and Trademark
 Office, Patent Trial and Appeal Board in Nos. IPR2017-
 00626, IPR2017-00627.
                  ______________________

                Decided: February 7, 2020
                 ______________________

     JEFFREY PAUL KUSHAN, Sidley Austin LLP, Washing-
 ton, DC, argued for appellant. Also represented by THOMAS
 ANTHONY BROUGHAN, III, CHRISTIN SULLIVAN MILLER.

    WILLIAM D. BELANGER, Pepper Hamilton LLP, Boston,
 MA, argued for appellee. Also represented by BRADLEY
 THOMAS LENNIE, GOUTAM PATNAIK, Washington, DC.
                ______________________

      Before DYK, PLAGER, and STOLL, Circuit Judges.
 PLAGER, Circuit Judge.
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 2                           APPLE INC. v. ANDREA ELECS. CORP.




     The patent at issue in this appeal, U.S. Patent No.
 6,363,345 (“the ’345 patent”), relates to certain aspects of
 digital audio processing. On September 19, 2016, Andrea
 Electronics Corp. (“Andrea or Appellee”), assignee of the
 ’345 patent, sued Apple, Inc. (“Apple or Appellant”) for in-
 fringement of the ’345 patent in the Eastern District of
 New York. J.A. 1151–70. On January 9, 2017, Appellant
 Apple filed two inter partes review (“IPR”) petitions—the
 ’626 IPR and ’627 IPR—with the U.S. Patent and Trade-
 mark Office, challenging the validity of claims 1–25 and
 38–47 of the patent.
      The Patent Trial and Appeal Board (“Board”) insti-
 tuted review of both petitions and consolidated the pro-
 ceedings. In its ’626 IPR Final Written Decision, the Board
 concluded that, in light of the prior art cited by Apple, all
 challenged claims except claims 4–11 and 39–47 of the ’345
 patent are unpatentable. In the course of reaching that
 conclusion, the Board declined to consider certain argu-
 ments in Apple’s ’626 IPR reply brief applicable to claims
 6–9 on the ground that Apple was raising new arguments
 in its reply brief that were not entitled to consideration at
 that late stage in the proceedings.
     In its ’627 IPR Final Written Decision, the Board con-
 cluded that, in light of other cited art, all challenged claims
 of the ’345 patent except claims 6–9, 17–20, 24, and 47 are
 unpatentable. In reaching that conclusion, the Board
 adopted a claim construction of the claim term “periodi-
 cally” in favor of Andrea that supported its analysis. Be-
 tween the two IPRs, the Board held that all challenged
 claims except claims 6–9 are unpatentable.
     With regard to the ’626 IPR Board decision, Apple ap-
 peals the Board’s conclusion that claims 6–9 are surviving
 claims, arguing that had the Board properly considered its
 reply brief arguments, that would not have been the out-
 come. With regard to the ’627 IPR Board decision, Apple
 argues that the Board erred in its conclusion that, based on
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 APPLE INC. v. ANDREA ELECS. CORP.                           3



 the prior art cited, claims 6–9 are not unpatentable as ei-
 ther anticipated or obvious.
     With respect to the ’626 IPR, for the reasons we shall
 explain, we conclude that the Board erred in refusing to
 consider Apple’s reply arguments. Accordingly, we vacate
 the Board’s decision in the ’626 IPR, and remand for recon-
 sideration of Apple’s reply brief arguments addressing the
 indicated prior art reference.
      With respect to the ’627 IPR, we find that the Board’s
 decision with regard to the validity of the patent claims in
 its ’627 IPR Final Written Decision was correctly reached.
 We therefore affirm the Board with respect to the ’627 IPR.
                       I. BACKGROUND
                A. Digital Audio Processing
      Because an understanding of the issues and our dispo-
 sition of them require some familiarity with the technology
 of sound and digital audio processing, we begin with that.
 Sound is the physical vibrations of a medium, such as air.
 These vibrations are often depicted in the form of a sinus-
 oidal wave, a “sine wave,” with time on the x-axis (horizon-
 tal), and the amplitude of the signal (roughly, volume) on
 the y-axis (vertical).




 J.A. 833.
 In addition to the amplitude, the frequency (cycles per pe-
 riod of time) of a sound wave is a particularly relevant
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 4                          APPLE INC. v. ANDREA ELECS. CORP.




 factor for human hearing. While amplitude roughly corre-
 sponds to volume, frequency corresponds to the pitch of the
 sound.
      Music and speech are generally comprised of sound at
 different frequencies (e.g., a musical chord consists of sev-
 eral notes played simultaneously). When multiple notes
 are played at the same time, the graphical representation
 of the resulting signal may look different from a simple sine
 wave:




 J.A. 836. The resulting graph is a composite of several dif-
 ferent sine waves, each corresponding to an individual fre-
 quency and amplitude. To determine which frequencies
 make up the signal, the signal can be converted to the fre-
 quency domain via a well-known mathematical formula
 called a “Fourier transform.”
     Digital signal processing frequently uses Fourier
 transforms to convert sounds between the time domain and
 frequency domain because it is computationally easier to
 make certain modifications to the signal in the frequency
 domain than in the time domain. This conversion to the
 frequency domain results in a histogram, in which the sig-
 nal is divided into “frequency bins” and each bin corre-
 sponds to one of the frequencies present in the signal. The
 magnitude of a particular frequency is represented on the
 y-axis.
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                     B. The ’345 Patent
      The patent at issue, the ’345 patent, describes a
 method, system, and apparatus that utilizes Fourier trans-
 forms and a process known as “spectral subtraction” for
 noise cancellation and reduction purposes. The disclosed
 system converts an audio signal to the frequency domain
 via Fourier transforms, sets separate thresholds for each
 “frequency bin” in order to distinguish the background
 noise, and then employs “spectral subtraction” to remove
 ambient noise without affecting speech and its characteris-
 tics. ’345 patent, col. 6 ll. 10–13.
     In order to determine the appropriate threshold for
 each frequency bin, the system sets two minimum values,
 which are described as a “future minimum” and a “current
 minimum.” ’345 patent, col. 6 ll. 23–41. At predetermined
 time intervals (e.g., every five seconds), the future mini-
 mum value is initialized as the value of the current magni-
 tude of the signal. ’345 patent, col. 6 ll. 24–28. Over that
 time interval, the future minimum is compared with the
 current magnitude value of the signal. If the observed
 magnitude is less than the value of the future minimum,
 then the future minimum is set equal to that newly ob-
 served lower value. ’345 patent, col. 6 ll. 24–32.
      At the start of each time interval, the current minimum
 is set as the value of the future minimum that was deter-
 mined over the previous time interval. ’345 patent, col. 6
 ll. 34–38. The current minimum value then follows the
 minimum value of the signal over the next time interval by
 comparing its value with the current magnitude value.
 ’345 patent, col. 6 ll. 34–38. The final current minimum
 value is used to calculate the adaptive threshold.
     This adaptive threshold is used in a process known as
 “spectral subtraction,” in which the value of the estimated
 “noise magnitude” is subtracted from the current magni-
 tude value of the bin. The result is a cleaner signal with
 some of the noise removed.
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 6                          APPLE INC. v. ANDREA ELECS. CORP.




                   C. The Claims at Issue
     Claims 6–9 of the ’345 patent are the only claims at is-
 sue in this appeal. Claims 6–9 depend from claim 5, which
 depends from claim 4, which depends from claim 1:
     1. An apparatus for cancelling noise, comprising:
     An input for inputting an audio signal which in-
     cludes a noise signal;
     A frequency spectrum generator for generating the
     frequency spectrum of said audio signal thereby
     generating frequency bins of said audio signal; and
     A threshold detector for setting a threshold for each
     frequency bin using a noise estimation process and
     for detecting for each frequency bin whether the
     magnitude of the frequency bin is less than the cor-
     responding threshold, thereby detecting the posi-
     tion of noise elements for each frequency bin.
 ’345 patent, col. 9 ll. 34–46 (emphasis added).
     Claim 4 adds features to the threshold detector, noting
 that the threshold detector “sets the threshold for each fre-
 quency bin in accordance with a current minimum value of
 the magnitude of the corresponding frequency bin; said
 current minimum value being derived in accordance with
 a future minimum value of the magnitude of the corre-
 sponding frequency bin.” ’345 patent, col. 9 ll. 54–60.
      Claim 5 adds that the “future minimum value is de-
 termined as the minimum value of the magnitude of the
 corresponding frequency bin within a predetermined pe-
 riod of time.” Thus claims 6–9 depend ultimately from
 claim 5, and place specific limits on how the “current min-
 imum value” or “future minimum value” are determined.
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 APPLE INC. v. ANDREA ELECS. CORP.                           7



 Claim 6 recites:
     The apparatus according to claim 5, wherein said
     current minimum value is set to said future mini-
     mum value periodically.
 ’345 patent, col. 9, ll. 65–67.
 Claim 7 recites:
     The apparatus according to claim 6, wherein said
     future minimum value is replaced with the current
     magnitude value when said future minimum value
     is greater than said current magnitude value.
 ’345 patent, col. 10, ll. 1–4.
 Claim 8 recites:
     The apparatus according to claim 6, wherein said
     current minimum value is replaced with the cur-
     rent magnitude value when said current minimum
     value is greater than said current magnitude
     value.
 ’345 patent, col. 10, ll. 5–8.
 Claim 9 recites:
     The apparatus according to claim 5, wherein said
     future minimum value is set to a current magni-
     tude value periodically; said current-magnitude
     value being the value of the magnitude of the cor-
     responding frequency bin.
 ’345 patent, col. 10, ll. 9–12.
                          II. The Issues
            A. The ’626 and ’627 IPR Proceedings
     As noted, Apple filed its two IPR petitions—the ’626
 IPR and the ’627 IPR—challenging claims 1–25 and 38–47
 of the ’345 patent. Relevant to this appeal, Apple alleged
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 8                           APPLE INC. v. ANDREA ELECS. CORP.




 that the challenged claims would have been anticipated or
 obvious in light of three pieces of prior art.
      In its ’626 IPR petition, Apple alleged that claims 6–9
 of the ’345 patent would have been obvious over Hirsch and
 Martin. Apple alleged in its ’627 IPR petition that claims
 6–9 are anticipated by Helf or would have been obvious
 over Helf and Martin. The Board instituted review on all
 challenged claims and grounds raised in both petitions and
 consolidated the two proceedings.
 The three pieces of prior art are:
 a. Rainer Martin, An Efficient Algorithm to Estimate the
  Instantaneous SNR of Speech Signals (1993) (“Martin”)
     Martin describes an algorithm for “instantaneous[ly]”
 estimating the “signal-to-noise” ratio of speech signals.
 J.A. 924. The Martin algorithm can be split into three ma-
 jor parts: (1) computation of a smoothed short time power
 estimate 𝑃𝑃�x(i) of signal x(i); (2) computation of the noise
 power estimate Pn(i); and (3) computation of the estimated
 signal-to-noise ratio of signal x(i) at time i, SNRx(i). J.A.
 924–25. The algorithm tracks varying noise power levels
 during speech activity over a defined number (“L”) of digi-
 tal samples, wherein each set of L samples corresponds to
 a portion of the signal, a “window,” e.g., 0.625 seconds. J.A.
 925. Each window of length L is further divided into addi-
 tional windows, or sub-windows (“W”). J.A. 925.
     One important consideration of the algorithm is
 whether the signal’s power is monotonically increasing for
 a given period of time—that is, whether “the minimum
 power of the last W windows . . . is monotonically increas-
 ing” for that period of time. J.A. 925. Martin requires at
 least two sub-windows (W ≥ 2) in order to determine
 whether a signal’s power level is monotonically increasing.
 J.A. 15. Under Martin’s approach, a scheme with no sub-
 windows (i.e., W = 1) cannot be used to determine whether
 the signal is monotonically increasing.
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 APPLE INC. v. ANDREA ELECS. CORP.                            9



  b. H.G. Hirsch & C. Ehrlicher, Noise Estimation Tech-
  niques for Robust Speech Recognition (1995) (“Hirsch”)
     The Hirsch reference describes improvements to the
 spectral subtraction process and provides algorithms for
 estimating the noise level of an audio signal. J.A. 920–21.
 Like the ’345 patent, one of the Hirsch algorithms utilize
 an “adaptive threshold” for each frequency bin of the audio
 signal to distinguish between noise and speech. Hirsch ex-
 plains that one advantage of using an adaptive threshold
 is that the methods estimate the noise levels “without an
 explicit speech pause detection.” J.A. 920. Hirsch refers to
 Martin as a “known” approach “to avoid the problem of
 speech pause detection and to estimate the noise charac-
 teristics just from a past segment of noisy speech.” J.A.
 920, 923.
            c. U.S. Patent No. 5,550,924 (“Helf”)
     Helf describes a system for “reducing the background
 noise of an input audio signal.” J.A. 964, col. 1, ll. 39–40.
 Helf’s claimed system similarly utilizes Fourier transforms
 to convert an audio signal into the frequency domain before
 calculating the estimated noise in each frequency bin. J.A.
 964, col. 1, ll. 54–61.
     Helf has two approaches for estimating the background
 noise in an audio signal: (1) a “stationary estimator” to
 compute a noise estimate, “Bk”; and (2) a “running mini-
 mum estimator” to compute a noise estimate “Mk.” Helf
 explains that the first approach, the method utilizing a sta-
 tionary estimator, is more accurate but requires one second
 intervals of solely background noise. J.A. 966, col. 6, ll. 33–
 39.
     The second approach, the method utilizing a running
 minimum estimator, is less accurate but develops back-
 ground noise estimates in ten seconds under any condi-
 tions. J.A. 966, col. 6, ll. 37–39. This approach calculates
 the differences between the noise estimate, Mk, and
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 10                          APPLE INC. v. ANDREA ELECS. CORP.




 previous background noise estimates according to a for-
 mula. J.A. 967, col. 8, ll. 54–57. If the overall difference
 exceeds a threshold, then Mk is used as the new back-
 ground noise estimate. This approach will only occur if two
 steps are met: (1) the noise estimates from the stationary
 estimator have not been updated for more than ten sec-
 onds; and (2) when the calculated value “D” of the Helf pa-
 tent exceeds a particular threshold. J.A. 967, col. 8, ll. 33–
 60.
                       1. The ’626 IPR
     In its ’626 IPR petition, Apple argued that Martin dis-
 closes the “current minimum” and “future minimum” limi-
 tations required by claims 6–9. According to Apple,
 Martin’s “noise floor estimation process” algorithm uses a
 “current minimum,” Pn(i), and a “future minimum,” PMmin,
 to track the minimum signal power, Px(i), during a prede-
 termined period. Apple asserted that a person having or-
 dinary skill in the art (a “POSA”) would have understood
 that Martin’s algorithm could also be used to track the
 “magnitude” of the noise signal, as required by claims 6–9
 of the ’345 patent. As an example, Apple’s expert witness,
 Dr. Hochwald, derived certain estimated noise floor values,
 Pn(i), and minimum observed noise power values, PMmin, by
 inputting certain variables. In this example, Dr. Hochwald
 assumed that there are no sub-windows (W = 1). J.A. 130–
 131.
     In its Patent Owner Response, Andrea argued that
 Martin does not disclose a “future minimum,” as required
 by claims 6–9. In support of this position, Andrea ex-
 plained that in both the “monotonically increasing” and the
 “non-monotonically increasing” applications of the algo-
 rithm, there is no future minimum and similarly utilized
 an example of the algorithm to demonstrate its point. J.A.
 280–91. Unlike Dr. Hochwald, however, Andrea’s expert
 witness, Dr. Douglas, applied Martin’s algorithm in the
 context of multiple sub-windows (W ≥ 2) because a
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 APPLE INC. v. ANDREA ELECS. CORP.                          11



 determination of whether a signal’s power is monotonically
 increasing over window length L requires at least two sub-
 windows. J.A. 925.
      Apple rebutted Andrea’s arguments on reply, respond-
 ing that Andrea mischaracterized Martin and read non-ex-
 istent limitations into the claims. First, Apple argued that
 where Martin is configured to use one sub-window (W = 1),
 it is not necessary to determine whether the sound is mon-
 otonically increasing. J.A. 463. Therefore, when there is
 only one sub-window, Martin discloses a future minimum
 because the Pn(i) value (current minimum) is set to the
 same PMmin value (future minimum), irrespective of which
 update equation is used. J.A. 464.
     Apple further argued that even under Andrea’s “multi-
 ple-sub-windows” application of the algorithm, the Martin
 algorithm still teaches a future minimum. J.A. 465–68.
 Apple contended that the claims do not specify the period
 over which the future minimum must be calculated, and as
 a result, in a scenario where a signal is monotonically in-
 creasing, Martin satisfies the claims. J.A. 467. Apple ar-
 gued that in cases where a signal is not monotonically
 increasing, the claims do not prohibit calculating the future
 minimum over a particular data window or using the min-
 imum of a previous sub-window as the “future minimum.”
      Apple submitted a reply expert declaration to support
 its analysis of the Martin algorithm in the context of mul-
 tiple sub-windows. Andrea subsequently deposed Apple’s
 expert witness for a second time but did not request au-
 thorization to file a sur-reply or move to strike any portion
 of Apple’s reply briefing. J.A. 252.
     During oral argument, the Board questioned whether
 Apple’s reply raised new arguments that were not other-
 wise discussed in the petition. J.A. 536–38 (13:5–15:18).
 In response, Apple pointed to the two pages in its petition
 addressing how the Martin algorithm teaches a noise floor
 estimation process that uses a “current minimum” and a
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 12                         APPLE INC. v. ANDREA ELECS. CORP.




 “future minimum” to track the minimum signal power dur-
 ing a predetermined period. J.A. 537 (14:3–21), J.A. 128–
 29.
                       2. The ’627 IPR
      In its ’627 IPR petition, Apple argued that Helf dis-
 closes the “periodically” limitation of claims 6–9. Claims
 6–9 recite a current and future minimum, wherein the two
 values are set “periodically.” In proposing a construction
 for the term, Apple relied on a definition provided by Web-
 ster’s Dictionary that defined “periodically” as “1: at regu-
 lar intervals of time” and “2: from time to time.” J.A. 2483.
 Apple took the position that both of these definitions apply
 to the term “periodically” in the context of the ’345 patent.
     With respect to its anticipation and obviousness argu-
 ments, Apple stated that Helf discloses a current minimum
 and future minimum that is set “periodically,” or “from
 time to time.” Reasoning that Helf’s running minimum es-
 timator sets the background noise estimate, Nk, (current
 minimum) to the running minimum estimate, Mk, (future
 minimum) whenever the difference between these values
 exceeds a threshold, Apple argued that this setting occurs
 “periodically,” or “from time to time.” J.A. 2483.
     Alternatively, Apple contended that Helf discloses the
 “periodically” limitation because, in cases where the sta-
 tionary estimator approach is not available (e.g., the audio
 signal continuously contains speech without any pauses),
 the current background noise estimate approach is set to
 the minimum estimate, Mk, 10 seconds after the system
 starts. J.A. 2483. Apple also argued that a POSA would
 have modified Helf’s system, in light of Martin, to update
 the current and future minimum values “at regular inter-
 vals of time.” Appellant Br. 62–63.
     In response, Andrea argued that the term “periodi-
 cally” should only be construed as “occurring at regular in-
 tervals of time,” and not “from time to time.” J.A. 2614. In
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 APPLE INC. v. ANDREA ELECS. CORP.                            13



 support of its position, Andrea explained that the ’345 pa-
 tent written description’s use of the term is only consistent
 with the first definition of “periodically.” J.A. 2615. For
 example, the written description only references the term
 once, when describing an embodiment of the invention,
 wherein “[t]he future and current minimum values are cal-
 culated continuously and initiated periodically, for exam-
 ple, every 5 seconds as determined in step 724 and control
 is advanced to steps 722 and 726 wherein the new future
 and current minimum are calculated.” ’345 patent, col. 8
 ll.36–40.
     Based on its proposed construction of “periodically,”
 Andrea argued that Helf does not disclose the “periodi-
 cally” limitation because Helf’s running minimum estima-
 tor does not set the current background noise estimate to
 the minimum estimate Mk at regular intervals of time. See
 J.A. 2632.
           3. The Board’s Final Written Decisions
     In its Final Written Decisions for the ’626 and ’627
 IPRs, the Board concluded that Apple had demonstrated
 that claims 1–5, 10–25, and 38–47 of the ’345 patent are
 unpatentable. The Board held, however, that in neither of
 the two IPRs had Apple demonstrated that claims 6–9 of
 the ’345 patent are unpatentable.
     With respect to the ’626 IPR, the Board concluded that
 a POSA would not have found it obvious to modify Hirsch’s
 system, based on a scenario from Martin where there are
 no sub-windows (W = 1). Importantly, the Board refused to
 consider Apple’s responsive arguments in its reply where it
 considered the Martin algorithm with multiple sub-win-
 dows (W ≥ 2), finding that these arguments raised a new
 theory of unpatentability for the first time in its reply brief.
     With respect to the ’627 IPR, the Board adopted An-
 drea’s proposed claim construction for “periodically” and
 construed the term to mean “at regular intervals of time.”
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 14                          APPLE INC. v. ANDREA ELECS. CORP.




 Based on this construction, the Board concluded that Apple
 failed to prove that Helf, alone or in combination with Mar-
 tin, discloses the “periodically” limitation as required by
 claims 6–9 of the ’345 patent.
                       III. DISCUSSION
  A. Was the Board Correct When It Determined That Ap-
  ple’s Reply Brief in the ’626 IPR Raised a New Theory of
                       Unpatentability?
     The Board’s determinations that a party exceeded the
 scope of a proper reply are reviewed for abuse of discretion.
 See Ericsson Inc. v. Intellectual Ventures I LLC, 901 F.3d
 1374, 1379 (Fed. Cir. 2018); Intelligent Bio-Sys., Inc. v. Il-
 lumina Cambridge Ltd., 821 F.3d 1359 (Fed. Cir. 2016).
 Apple contends that the Board abused its discretion by re-
 fusing to consider arguments and evidence that Apple ad-
 vanced in its ’626 IPR reply brief.
      “It is of the utmost importance that petitioners in the
 IPR proceedings adhere to the requirement that the initial
 petition identify ‘with particularity’ the ‘evidence that sup-
 ports the grounds for the challenge to each claim.’” See In-
 telligent Bio-Sys., 821 F.3d at 1369 (citing 35 U.S.C.
 § 312(a)(3)). And “[a] reply may only respond to arguments
 raised in the corresponding opposition, patent owner pre-
 liminary response, or patent owner response.” 37 C.F.R.
 § 42.23(b). Therefore, in determining whether Apple ap-
 propriately advanced its arguments regarding the applica-
 tion of the Martin algorithm with multiple sub-windows
 (W ≥ 2), we must consider: whether the petitioner’s reply
 brief is responsive to arguments originally raised in its pe-
 tition; or whether the reply arguments are responsive to
 arguments raised in the patent owner’s response brief.
    Andrea contends that the Board correctly precluded
 Apple’s arguments applying the Martin algorithm with
 multiple sub-windows because Apple’s ’626 IPR petition
 was “intentionally” premised on a scenario in which there
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 APPLE INC. v. ANDREA ELECS. CORP.                          15



 were no sub-windows (W = 1). Andrea argues that Apple’s
 multiple sub-window discussion is a “new theory of un-
 patentability,” particularly because the accompanying ex-
 pert declaration to Apple’s petition relied solely upon a
 scenario wherein W = 1.
     We disagree. Apple’s legal ground did not change in its
 reply—its reply still asserted that claims 6–9 would have
 been obvious over Hirsch and Martin. Moreover, Apple’s
 reply relies on the same algorithm from the same prior art
 reference to support the same legal argument: that Martin
 discloses the “current minimum” and “future minimum”
 limitations of the asserted claims.
     Indeed, Apple’s reply arguments regarding Martin are
 not the types of arguments that we have previously found
 to raise a “new theory of unpatentability.” For example, in
 Ariosa Diagnostics v. Verinata Health, Inc., the Board re-
 jected the petitioner’s reliance on its reply submissions be-
 cause the petitioner discussed “previously unidentified
 portions of a prior-art reference to make a meaningfully
 distinct contention.” 805 F.3d 1359, 1367 (Fed. Cir. 2015).
 The reply declaration pointed to an embodiment of the
 prior art that was not discussed in the petition. Id. Ac-
 cordingly, we held that the Board reasonably determined
 that the reply declaration raised a new argument that was
 not otherwise addressed in the petition.
     Similarly, in Intelligent Bio-Systems, we concluded
 that the reply brief and accompanying declaration ex-
 ceeded the scope of the petition when the petitioner cited
 several new non-patent literature references and argued
 that a POSA would have considered the claim obvious for
 reasons other than those described in the originally relied-
 upon prior art. 821 F.3d at 1369.
     Unlike the above cases, Apple’s reply does not cite any
 new evidence or “unidentified portions” of the Martin ref-
 erence. Apple’s reply brief merely demonstrates another
 example of the same algorithm to further explain why
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 16                          APPLE INC. v. ANDREA ELECS. CORP.




 Martin discloses the “current minimum” and “future mini-
 mum” limitations of claims 6–9. The Board “pars[es] [the
 petitioner’s] arguments on reply with too fine of a filter.”
 See Ericsson Inc., 901 F.3d at 1380. It is unreasonable to
 hold petitioners to such a high standard that, if they choose
 to rely on one example of an algorithm, they must either
 discuss all potential permutations of the variables or risk
 waiving the opportunity to further discuss other relevant
 examples in their reply. Chamberlain Grp., Inc. v. One
 World Techs., Inc., 944 F.3d 919, 925 (Fed. Cir. 2019) (“Par-
 ties are not barred from elaborating on their arguments on
 issues previously raised.”).
      Further, any ambiguity as to whether Apple raised a
 new argument on reply is eliminated when we consider
 whether Apple’s reply arguments are responsive to argu-
 ments raised in Andrea’s Patent Owner Response. 1 As we
 have regularly held, “the petitioner in an inter partes re-
 view proceeding may introduce new evidence after the pe-
 tition stage if the evidence is a legitimate reply to evidence
 introduced by the patent owner.” Anacor Pharm., Inc. v.
 Iancu, 889 F.3d 1372, 1380–81 (Fed. Cir. 2018).
      In its opposition, Andrea argued that Apple’s argument
 is inherently flawed because Martin requires at least two
 sub-windows in order to perform one step of the algorithm.
 Andrea’s response brief devoted at least seven pages to its
 discussion about why the Martin algorithm, in the context
 of multiple sub-windows, does not disclose a “future mini-
 mum.” J.A. 287–293. Apple’s reply squarely responds to
 Andrea’s Patent Owner Response. In addition to rebutting
 Andrea’s arguments addressing the W = 1 scenario, Apple
 argued that Andrea’s multiple sub-window discussion


      1 Notably, neither the Board nor Andrea addressed
 whether Apple’s reply arguments are responsive to those
 arguments raised in Andrea’s Patent Owner response. J.A.
 15; Appellee Br. 50–65.
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 APPLE INC. v. ANDREA ELECS. CORP.                          17



 “reads non-existent limitations into the claims” and why
 the algorithm, even in the context of multiple sub-windows,
 discloses a “future minimum.” J.A. 465–68.
     Stepping back a bit of distance persuades us that the
 Board’s decision to ignore Apple’s responsive arguments to
 issues raised by Andrea in its Patent Owner Response is
 not supported as a matter of law; the conclusion that the
 reply brief constitutes an impermissible new matter is an
 abuse of discretion.
  B. Would a POSA Have Understood the Claim Term “Pe-
     riodically” to Mean “At Regular Intervals of Time”?
     The Court reviews the construction of a claim term by
 the Board without deference. Teva Pharm. USA, Inc. v.
 Sandoz, Inc., 574 U.S. 318, 332–33 (2015). Subsidiary fac-
 tual findings are reviewed for substantial evidence.
 Knowles Elecs. LLC v. Iancu, 886 F.3d 1369, 1374 (Fed. Cir.
 2018). When this court reviews the claim construction of a
 patent claim term in an IPR appeal after the patent has
 expired, such as in this case, we apply the standard estab-
 lished in Phillips, not the “broadest reasonable interpreta-
 tion.” See In re CSB-System Int’l, Inc., 832 F.3d 1335, 1342
 (Fed. Cir. 2016); Microsoft Corp. v. Enfish, LLC, 662 F.
 App’x 981, 984 (Fed. Cir. 2016).
     Apple argues that, with respect to the ’627 IPR, the
 Board erred because it did not construe “periodically” to
 also mean “from time to time.” Appellant Br. 51.
     We disagree. The written description’s only use of the
 term “periodically” supports the Board’s construction. The
 written description recites: “The future and current mini-
 mum values are calculated continuously and initiated pe-
 riodically, for example, every 5 seconds as determined in
 step 724 and control is advanced to steps 722 and 726
 wherein the new future and current minimum are calcu-
 lated.” ’345 patent, col. 8, ll. 36–38 (emphases added). The
 written description affirmatively illustrates calculating the
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 18                         APPLE INC. v. ANDREA ELECS. CORP.




 future and current minimum values “every 5 seconds” or
 within a “regular interval of time.” ’345 patent, col. 8, ll.
 36–38.
     We recognize that preferred embodiments do not act as
 claim limitations, but when the invention as claimed covers
 only the preferred embodiment described in the written de-
 scription, it is questionable whether a patentee may assert
 a proposed construction that is broader than the plain lan-
 guage of the claim. See Phonometrics, Inc. v. N. Telecom
 Inc., 133 F.3d 1459, 1466 (Fed. Cir. 1998) (“Although
 claims are not necessarily restricted in scope to what is
 shown in a preferred embodiment, neither are the specifics
 of the preferred embodiment irrelevant to the correct
 meaning of claim limitations.”). Here, the written descrip-
 tion’s only reference to “periodically” supports the Board’s
 conclusion that a POSA would have understood this term
 to mean “at regular intervals of time” rather than “from
 time to time.”
     Apple also argues that the “periodically” term should
 be construed to mean “from time to time” because the ’345
 patent discloses setting the future minimum value to a cur-
 rent magnitude value whenever “the smoothed estimate [of
 the current magnitude Y(n)] is less than the calculated fu-
 ture minimum value.” Appellant Br. 51–52 (citing ’345 pa-
 tent, col. 8, ll. 36–40). Apple contends that this “smoothed
 estimate” update is an example of setting the minimum
 values “from time to time,” and argues that in order “to be
 consistent” with the intrinsic evidence, “periodically” must
 be construed to encompass both ways of updating the val-
 ues. Apple asserts that to adopt the Board’s limited con-
 struction would affirm “a claim construction that excludes
 the preferred embodiment.” Reply Br. 7.
     This argument is unconvincing. Even assuming that
 the ’345 patent addresses different ways of setting the fu-
 ture and current minimum values, Apple conflates the
 written description’s disclosures of two different methods
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 APPLE INC. v. ANDREA ELECS. CORP.                              19



 of setting minimum values with the separate limitation of
 setting these values on a periodic basis. In fact, claims 6–
 9 of the ’345 patent do not capture the “smoothed estimate
 value” method described in the ’345 patent—nor do they
 need to.
     As we have held, “[when] the patent describes multiple
 embodiments, every claim does not need to cover every em-
 bodiment. This is particularly true [when] the plain lan-
 guage of a limitation of the claim does not appear to cover
 that embodiment.” Pacing Techs., LLC v. Garmin Int’l,
 Inc., 778 F.3d 1021, 1026 (Fed. Cir. 2015) (internal cita-
 tions omitted). The plain language of the claims-at-issue
 does not cover the “smoothed estimate” method. Rather,
 other claims, such as claims 23, 36, and 45 of the ’345 pa-
 tent, which do not include the “periodically” term, discuss
 a method of determining future minimum values based on
 “the step of smoothing the estimate of each frequency bin.”
 See, e.g., ’345 patent, col. 12, ll. 4–54. We decline to extend
 the scope of the “periodically” term beyond the plain text of
 the intrinsic record.
      Nor does the extrinsic evidence help Apple’s position.
 The Board relied on the testimony of Dr. Douglas, Andrea’s
 expert witness, who opined that the Board’s construction is
 the “only . . . definition . . . consistent with the specification
 of the ’345 patent and its use in the particular field of audio
 signal processing.” J.A. 33. Specifically, Dr. Douglas ex-
 plained that the “period” of an audio signal is the amount
 of time it takes for a signal to repeat, and that this amount
 of time occurs at regular intervals. Id.
     Moreover, Apple’s expert witness admitted during his
 deposition that, “out of the context of the ’345 [patent],” the
 definition of “periodically” is “at regular time intervals.”
 J.A. 33. When asked what he perceived “periodically” to
 mean in the context of the ’345 patent written description,
 Apple’s expert simply responded that “all I can do is read
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 20                          APPLE INC. v. ANDREA ELECS. CORP.




 what it says,” which is “that “[i]t’s doing something period-
 ically, for example, every five seconds.” Id.
      We have regularly held that extrinsic evidence in the
 form of expert testimony can “provide background on the
 technology at issue” and “ensure that the court’s under-
 standing of the technical aspects of the patent is consistent
 with that of a person of skill in the art, or to establish that
 a particular term in the patent or the prior art has a par-
 ticular meaning in the pertinent field.” Phillips v. AWH
 Corp., 415 F.3d 1303, 1318 (Fed. Cir. 2005). Here both par-
 ties’ experts offered testimony in favor of the Board’s con-
 struction of “periodically” as limited to “at regular intervals
 of time.” We find that the Board’s subsidiary factual find-
 ings with respect to how a person skilled in the art would
 have understood the “periodically” limitation are sup-
 ported by substantial evidence. Knowles Elecs., 886 F.3d
 at 1374.
     Accordingly, because the ’345 patent’s written descrip-
 tion and the claim language support a construction of “pe-
 riodically” as “at regular intervals of time” and not “from
 time to time,” and because there is substantial evidence
 that a person skilled in the art would have understood the
 term to be limited to “at regular intervals of time,” we con-
 clude that the Board did not err in its construction of the
 “periodically” term.
    C. In the ’627 IPR Proceedings, Did Apple Satisfy Its
  Burden of Proving That Claims 6–9 of the ’345 Patent Are
         Anticipated or Would Have Been Obvious?
     Apple argues that, even under the Board’s construction
 of “periodically,” the Board erred in its ’627 IPR finding
 that Apple failed to prove that claims 6–9 are anticipated
 or would have been obvious.
     We disagree. With respect to its anticipation argu-
 ment, Apple asserts that Helf discloses the “periodically”
 limitation because its running minimum estimator sets the
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 APPLE INC. v. ANDREA ELECS. CORP.                          21



 background noise estimate, Nk, to the minimum estimate,
 Mk, at regular intervals of time. Appellant Br. 58. But sub-
 stantial evidence supports the Board’s findings that Helf’s
 running minimum estimator does not meet the “periodi-
 cally” limitation. See Nobel Biocare Servs. AG v. Instradent
 USA, Inc., 903 F.3d 1365, 1375 (Fed. Cir. 2018) (“Anticipa-
 tion is a question of fact that we review for substantial ev-
 idence.”).

      As described above, Helf discloses two approaches for
 estimating the background noise in an audio signal: (1) a
 stationary estimator method; and (2) a running minimum
 estimator method. Helf’s running minimum estimator
 method is a “back-up” approach. That is, the Helf system
 does not employ the running minimum estimator method
 unless the system cannot employ the stationary estimator
 approach. J.A. 966, col. 6, ll. 33–39. Helf explains that the
 system is set up in this configuration because the station-
 ary minimum estimator is “more accurate,” but requires
 one second intervals of solely background noise. J.A. 966,
 col. 6, ll. 35–39.

     Accordingly, the system employs a “running minimum
 estimator” in the alternative, which is less accurate but de-
 velops background noise estimates in ten seconds “under
 any conditions.” J.A. 966, col. 6, ll. 37–39. The background
 noise estimate update will not occur unless other condi-
 tions are met, such as when an algorithm determines that
 the difference between Mk and the past background noise
 estimate exceeds a certain threshold. J.A. 967, col. 8, ll.
 10–60.

     Under this configuration, Helf cannot satisfy the “peri-
 odically” limitation because it does not update the noise es-
 timate Mk or Nk, which Apple alleges is the “current
 minimum,” at regular intervals of time. The running min-
 imum estimator approach only updates the background
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 22                          APPLE INC. v. ANDREA ELECS. CORP.




 noise estimate if the stationary estimator approach is una-
 vailable and if certain conditions are met.

      In response, Apple argues that in situations where only
 the running minimum estimator can operate, the back-
 ground noise estimate, Nk, is set to the minimum estimate,
 Mk, “10 seconds after the system starts.” Appellant Br. 58
 (citing J.A. 967, col. 8, ll. 33–43). Apple contends that the
 update that occurs “10 seconds after the system starts” oc-
 curs “periodically.” Appellant Br. 58. But this update does
 not occur “at a regular interval.” It occurs once, after the
 running minimum estimator is activated.

     Although Apple insists that the “periodically” limita-
 tion also may be met if the Helf system is “power-cycled on
 and off,” Reply Br. 26, such an argument is unavailing. Not
 only does the suggestion of “power-cycling” the system de-
 feat the purpose of the “periodically” limitation, but it also
 requires a user to power-cycle the Helf system at regular
 intervals because any delay would modify the amount of
 time between each background noise estimate update. We
 decline to read such a strained interpretation of the prior
 art so as to obviate the claimed limitation.
     Similarly, we find that the Board did not err in its con-
 clusion that Helf, in combination with Martin, does not dis-
 close the “periodically” limitation. Apple asks us to
 overrule the Board’s fact-intensive inquiry as to whether a
 person skilled in the art would have been motivated to com-
 bine Helf and Martin to develop a system that updates the
 current and future minimum values “at regular intervals.”
 We decline that invitation. Corning v. Fast Felt Corp., 873
 F.3d 896, 902 (Fed. Cir. 2017).
     Substantial evidence supports the Board’s finding, par-
 ticularly when Dr. Hochwald’s testimony on the motivation
 to combine issue consisted of one paragraph of conclusory
 statements. See J.A. 2935–36.
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 APPLE INC. v. ANDREA ELECS. CORP.                          23



     Having determined that substantial evidence supports
 the Board’s finding that a person skilled in the art would
 not have been motivated to combine Martin with Helf so as
 to modify the running minimum estimator by adding up-
 dates to the background noise estimate, Nk, and the run-
 ning minimum estimate, Mk, “every ten seconds during
 operation of the running minimum estimator,” we conclude
 that Helf, in combination with Martin, does not render ob-
 vious the “periodically” limitation, as required by claims 6–
 9 of the ’345 patent. 2
                       IV. CONCLUSION
     For the reasons stated above, we vacate the Board’s
 findings in the ’626 IPR and remand for consideration of
 the arguments raised by Apple in its ’626 IPR reply brief.
 We affirm the Board’s findings in the ’627 IPR.
   AFFIRMED-IN-PART, VACATED-IN-PART, AND
                 REMANDED




     2    Apple also argues that the Board’s rejection of Ap-
 ple’s proposed modification for Helf, in light of Martin, only
 relates to claim 6 and not claim 9 because claim 9 specifies
 updates to the “future minimum value” (as opposed to up-
 dates to the “current minimum value”). Appellant Br. 64;
 Reply Br. 31. Apple misunderstands the Board’s reason-
 ing. The Board concluded that a person skilled in the art
 would not have modified the “running minimum estimator”
 to update at regular ten second intervals—such a conclu-
 sion applies equally to both the background noise estimate
 and running minimum estimate Mk that are set by the run-
 ning minimum estimator. J.A. 47–48.
