The SPEED knob smoothly changes the playback speed from forward to reverse when turned counterclockwise. Moving the knob closer to the middle will cause the pitch to drop as the audio is slowed down, similar to an analog recording.
When playback is reversed, short segments of the live audio are read backwards, simulating studio tricks where a tape is flipped over to create a reverse guitar solo. Tensor analyzes your playing to automatically adjust the size and timing of the reversed segments.