From Bose Portable PA Encyclopedia
- Setting the Trim Control
- Set the Trim control on the power stand to the 0 (zero) position.
- Connect the audio source to the Analog Input
- Adjust the volume of the source device output to the reference or nominal output level.
- On analog consoles this may be marked as unity or 0 dB.
- On digital consoles this may be marked as -18 dBFS[1][2]. The exact value (-18 dBFS to -20 dBFS) may vary depending your location[3].
- Refer to the manual for the source device for details.
- If the source device does not have metering or indicators, set the output as high as you can without hearing distortion or seeing red indicator lights.
- While playing/singing as loud as you will during your performance, increase the Trim level so that the Signal/Clip indicator glows green or yellow. Occasional flickers of red are okay.
- If the Signal/Clip indicator glows solid red or you hear distortion, decrease the Trim level so that it glows only green or yellow.