Pioneer Dj DDJ-FLX4 Portable 2-Channel rekordbox DJ and Serato Controller (Graphite) - Manual (Page 29)

Part names and functions
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6 EQ (HI, MID, LOW) knobs
Boost or reduce the relevant frequency for the selected channel.
7 MIC LEVEL knob
Adjusts the volume of input sound from the [MIC] input terminal.
8 CFX knobs
When the [SMART CFX] button is off:
Control the filter effect for each channel.
When a knob is set to the center position, the sound is unchanged.
Turn counterclockwise:
Gradually decreases the low-pass filter's cutoff frequency.
Turn clockwise:
Gradually increases the high-pass filter's cutoff frequency.
When the [SMART CFX] button is on:
Control Smart CFX for each channel.
When a knob is set to the center position, the sound is unchanged.
9 SMART CFX button
Press:
Turns Smart CFX mode (Preset 1) on/off.
[SHIFT] + press:
Turns Smart CFX mode (Preset 2) on/off.
10 Headphones CUE buttons (channel)
Press:
Play the sound of the relevant channel through your headphones.
[SHIFT] + press:
Hold the [SHIFT] button and tap the headphones [CUE] button to set the
tempo of the respective deck in time with your tapping. (Tapping function)