Hybrid Audio, LLC v. ASUS Computer International, Inc.

Background

Hybrid Audio, LLC brought a patent-infringement suit against ASUS Computer International, Inc., and other defendants. Hybrid accused ASUS of infringing United States Reissue Patent No. RE40,281, which concerns audio signal processing. The patent describes methods that split a signal into subbands using filter banks arranged in a tree structure; the subbands may approximate frequency bands of the human auditory system.

The order addressed claim construction, which is the court’s interpretation of disputed words and phrases in patent claims. The parties initially identified 19 disputed terms, although the court’s Standing Order required permission to identify more than 10. By the time of the order, the parties had narrowed the dispute to the meaning of “signal processing.”

Agreed and Undisputed Terms

The court adopted the parties’ agreement to use several provisional constructions from an earlier related case. These included definitions for “filter banks,” “tree structured array,” “sub-band component,” “root node,” “leaf node,” “synthesis,” and “modulating.” The court also adopted constructions for “cosine modulation” and “polyphase components.”

The parties agreed that “plurality of filter banks” and “splitting signal into subbands using a plurality of filter banks” required no construction beyond the definition of “filter banks.” For seven other terms—“audio information,” “audio signal,” “signal is an audio signal,” “first level,” “second level,” “512 samples,” and “window comprising 512 samples”—neither party proposed a definition. The court declined to construe those terms separately and stated that their plain and ordinary dictionary meanings would apply.

Construction of “Signal Processing”

Hybrid proposed defining “signal processing” as “digital signal processing.” ASUS proposed the plain and ordinary meaning without limiting the term to digital processing. The court concluded that the patent’s specification showed that the claimed signal-processing methods use digital signals.

The court noted that the patent says an input signal is preferably digital and that an analog signal must pass through an analog-to-digital converter before being processed through the filter banks. The specification also describes the signals as digitized and states that signals stored in a shift register represent the next signal segment in digital form. ASUS identified nothing contrary and did not show that digital implementation was merely one optional embodiment.

Ruling

The court construed “signal processing” to mean “digital signal processing.” The order interpreted the patent language but did not decide whether ASUS infringed the patent.