Is only one deck playing back light shows?
If this is the case you may need to activate the crossfader link button in Serato Video.
Note: You DO NOT need Serato Video running in order to use SoundSwitch.
SoundSwitch requires the X-F Link button in Serato Video to be active in order to sync with the crossfader position.
Step 1: Open Serato Video
Step 2: Check if the X-Fader link button is active
Press to Activate
Also, insure that both LINK buttons are enabled on the upfaders
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