methods and apparatuses are provided to identify and extract a torque ripple signal found in the back - emf signal from an electric motor . the torque ripple signal is used in a feedback control loop to reduce the amount and effects of torque ripple in the motor and the motor system . a motor controller is provided to reduce torque ripple in an electric motor . the motor controller is suitable for controlling the speed or torque or other related parameters associated with the electric motor . a disc drive apparatus for use in information storage and retrieval systems is provided . the disc drive apparatus includes an electric motor , an information storage disc , and a motor controller . a method is provided for reducing the effects of torque ripple in an electric motor by sampling the back - emf signal generated by the electric motor , extracting the torque ripple signal from the back - emf signal , and generating an ac component signal proportional to the torque ripple signal . this ac component signal is then used to create an error - correcting feedback control signal that can be used to modify the drive signal supplied to the motor such that the torque ripple in the motor is reduced . this method may be embodied using analog or digital circuitry , or a combination thereof .