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From Unreal Wiki, The Unreal Engine Documentation Site
Wrapper for other Sounds or SoundGroups to randomize playback pitch within certain limits. Unlike the properties suggest, volume modification doesn't seem to be applied. Pitch modification is calculated as percentage of original pitch, similar to the following expression:
1.0 + (PitchModification / 100.0) + (FRand() * PitchVariance / 100.0)
 Property group 'Sound'
The sound to modify.
Base pitch modification in percent of original pitch. Typically this value is a negative whole number with half the absolute value of PitchVariance if the modified pitch should be spread around the original pitch, e.g. -5.
Pitch randomization in percent of original pitch. Typically this value is a positive whole number with twice the absolute value of PitchModification if the modified pitch should be spread around the original pitch, e.g. 10.
 Internal variables
Currently used pitch modification.