If there is no sound, or the volume is too low, on the Roland GO:MIXER PRO-X, check the following.
HEADPHONE/SMARTPHONE OUT knob
This knob controls both the headphone volume and the overall volume recorded to your smartphone. If it is turned down, you will not hear sound and it will not be recorded. Raise the knob, adjusting it so the sound does not distort.
SMARTPHONE IN/OUT jack requires battery power
If you are using the SMARTPHONE IN/OUT jack (3.5mm analog connection) instead of USB, the GO:MIXER PRO-X must be running on battery power. It will not function over this jack when powered only by the smartphone via USB.
Smartphone volume
If your smartphone's own volume is turned down, you will not hear playback sound. Adjust the volume on your smartphone.
Note: Audio recorded through the GO:MIXER PRO-X may sound softer on playback than it did while recording. This is expected behavior, not a malfunction.