Hollins M. (Aug, 2017). Pacinian Signals Determine the Direction and Magnitude of the Effect of Vibration on Pain. Perception, 46(8), 987-999.
"Intermittent vibration was used to minimize peripheral vibratory adaptation. Pain records at 12 and 50 Hz were similar; pooling them revealed significant hypoalgesia at the highest amplitude. At 80 Hz, in contrast, the middle amplitude produced hypoalgesia, but a significant shift toward hyperalgesia occurred at the highest amplitude."
High frequency, low amplitude is best at pain relief.