Pioneer Dj DDJ-FLX10 4-Channel DJ Controller for rekordbox and Serato DJ Pro (Black) - Manual (Page 57)

Part names and functions
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5 BEAT FX select knob
Changes the FX.
6 BEAT FX CH select knob
Changes the channel that the effect will be applied to.
7 BEAT FX LEVEL/DEPTH knob
Adjusts the parameter of FX.
8 BEAT FX ON/OFF button
Press:
Turns FX on/off.
9 BEAT FX indicators
Light up for the channel selected with the BEAT FX CH select knob.
When
[MST] is selected, the indicators of all channels light up.
When FX is turned on, the indicator flashes on the channel to which the effect
is applied.
10 COLOR knobs
Change the parameter of Sound Color FX for each channel.
11 SOUND COLOR FX buttons
Turn Sound Color FX on/off.
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Read: Using Sound Color FX (page 148)