Transformative Engineering Audio Injector Allows Signal Substitution in HDMI Path Transformative Engineering's HAI-1 Audio Injector is a patent-pending device that allows a user to substitute audio in an HDMI signal path.RS Staff ⋅ Sep 29, 2015 Transformative Engineering’s HAI-1 Audio Injector is a patent-pending device that allows a user to substitute audio in an HDMI signal path. Typical applications, according to the company, include injecting the center channel information so a TV’s speakers can be used as the center channel. The resulting effect eliminates the need for a separate center-channel speaker. Another use may be injecting a local microphone preamp signal in an educational or corporate environment to utilize the TV’s internal amplifier and speakers. This eliminates the need and cost of a separate amplifier, speakers, and installation. The HAI-1 has one HDMI input and one output, stereo RCA line-level inputs, and high-level speaker audio inputs. In center-channel applications, speaker input would be connected to an AV receiver’s center-channel output. The RCA jacks are used to inject line-level mono or stereo signals into the HDMI signal, and may be used to play independent audio sources such as a local microphone for narration or CD/MP3 player for background music through the TV’s audio system. The HAI-1 also has a USB port for firmware updates.