A disk drive is disclosed for connecting to a host, the host comprising loopback circuitry operable to loop a pattern received from the disk drive back to the disk drive. The disk drive comprises interface circuitry including a transmitter driver operable to transmit transmission signals at a transmission amplitude, and a receiver driver operable to receive reception signals. The transmitter driver is configured to transmit at an initial transmission amplitude, and a calibration pattern is transmitted to the host through the transmitter driver. The reception signals received by the receiver driver are monitored to detect a loopback pattern representing a loopback of the calibration pattern. The loopback pattern is processed to detect an error, and the transmission amplitude is adjusted in response to the error.