The BA7725S and BA7725FS are analog companders designed for KARAOKE echo systems, and logarithmically compress the signal level by 1 / 2 and then logarithmically expand it by a factor of 2. These ICs can be used in combination with the BU9252S or BU9252F to create a digital echo system. These ICs have an internal line mixer amplifier for mixing line input and echo signals. The internal electronic volume control makes it possible to adjust the mixer level and loop level mixer with an external DC voltage.