Barium Duo is a dual channel Peak Signal Meter. Two rows of 20 LED’s which each have a range of 42 dB with dBu and dBFS scale. To allow Barium Duo to read two channels, both input and output of the 500 module are used. To get 2-channels in (left / right) Barium Duo comes with an XLR Female-to-Female adapter for your 500 rack. Left channel comes from the input, right channel comes from the output (using the adapter). As a consequence, Barium Duo does not have signal-through, so you’ll need to split the signal to feed Barium Duo. But Barium Duo has the advantage of 2 channels in one single module (at a low cost).