Complex sentence: In the mid- 1970s Market consulted with Battle in an attempt to create an upgrade the EP-3 designated the EP-4 by adding features such as an input meter, tone controls, and a compander circuit to lower the noise of the tape playback.
Split into simpler sentences: In the mid- 1970s Market consulted with Battle in an attempt to upgrade the EP-3 by adding features such as an input meter and tone controls. They also added a compander circuit to lower the noise of the tape playback.