TL Audio PA-1 - Manual (Page 9)

Phase Reverse.
Channel A features a phase reverse switch, which may be used to correct a phase error
introduced elsewhere in a stereo signal path being processed by the Pre-Amplifier. A
phase error typically appears as a loss of low frequency signal content, due to
cancellation of out of phase components.
LED Level Indicators.
Each channel has a 3 segment LED meter to indicate the internal operating level of the
Pre-Amplifier. The meters monitor the pre-fade headroom level, illuminating at the
following points:
Signal: -20dBu,
Peak:
+18dBu,
Clip: +24dBu (2dB of headroom remaining).