Yamaha U1-SILENT Owner's Manual page 22

Example: Using AUX IN
■ When connected to other sound modules or playback devices (such as CD
players):
You can use the Silent Piano function together with the sound received from the connected devices.
You can use the VOLUME control on this unit to simultaneously adjust the volume of its electronic sound and
the sound received through its AUX IN jack. Adjust the output volume on the connected device to balance the
sounds.
USB
IN MIDI
OUT MIDI
OUT IN
AUX
Caution
Do not connect the output jack of an analog recording device to this unit's AUX IN jack if you have connected this
unit's AUX OUT jack to the input jack of the same recording device. Doing so will cause feedback of the audio signal
which may damage both components.
16
Other sound modules
OR
CD player etc