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  1.   How to Reduce Audible Noise in Stepper Motors
    1.     Trademarks
    2. 1 Introduction
    3. 2 Details of the Test Setup
    4. 3 Sources of Noise in a Stepper Motor
      1. 3.1 Magnetic Noise
      2. 3.2 Mechanical Noise
      3. 3.3 Electrical Noise
        1. 3.3.1 Effects of Current Ripple and Decay Mode
        2. 3.3.2 Effects of PWM Chopper Frequency
        3. 3.3.3 Effects of Current Zero-cross Error
        4. 3.3.4 Effects of Step Resolution and Step Frequency
        5. 3.3.5 Effects of Resonant Frequency
    5. 4 Summary
    6. 5 References

3.3.5 Effects of Resonant Frequency

Each stepper motor has a resonant frequency. This is the reason why a stepper motor does not stop immediately when it performs a step, but continues to move slightly forward and backward. The amount of time the motor oscillates is called its settling time. The rate of oscillation matches the resonant frequency. The result is a motor that vibrates and has jitter and noise. If the system damping is low, the resonance can overpower the magnetic field between the stator and the rotor, resulting in lost steps and audible noise.

Once again, microstepping offers an easy and safe way to eliminate resonance, because by increasing the level of microstepping, step frequency can be made higher than the resonant frequency. Dampers are also used to reduce resonances and audible noise. Dampers work by absorbing shock to reduce impulses and dissipating the kinetic energy in resonances. This can eliminate noise, enhance the system transient response and reduce settling time.