Yamaha QY100 Owner's Manual page 37

For Guitarists: Outstanding Amp Simulation & Effects
x Adjust the input gain.
Use the GAIN control on the rear panel to adjust the QY100
input gain to match your guitar. If the PEAK indicator LED next to
the [PARAMETER] button light more than just occasionally as you
play, the GAIN setting is too high. The PEAK indicator should flash
only briefly on the highest transient peaks.
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