In June that year, while the companies were still talking, Apple filed U.S. patent application covering a system for suppressing noise in a signal while retaining the user's voice.

Noise Free's complaint alleges Apple "extracted Noise Free's proprietary and confidential object code, determined Noise Free's noise reduction software and measured and duplicated the signal traces from the circuit board and microcontroller," and supplied the information to Audience.

Further, it says the Apple patent filing contains some of the ideas and inventions it disclosed to Apple.

Apple and Noise Free did not return calls for comment.

Noise Free Wireless, based in nearby Santa Clara, is asking the U.S. District Court for the Northern District of California to find Apple misappropriated trade secrets, breached contract, and engaged in unfair business practices. It wants damages for the alleged patent infringement and an invalidation of Apple's patent.