Yamaha QY100 Owner's Manual page 46

For Singers: Cool Vocal Processing
x Adjust the input gain.
Use the GAIN control on the rear panel to adjust the QY100
input gain to match your microphone. If the PEAK indicator LED
next to the [PARAMETER] button light more than just occasionally
as you sing, the GAIN setting is too high. The PEAK indicator
should flash only briefly on the highest transient peaks.
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