# Motor PWM Frequency?



## DavefromMD (Jul 25, 2013)

What is motor PWM frequency (CV9) and what exactly does it do?

I see it can be set, but how do you know what to set it to?

What effect does it have on a locomotive?


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## D&J Railroad (Oct 4, 2013)

That is a feature that was designed back in the early days of DCC to make the motor stop singing at low speed. Pulse Width Modulation. It varies the width of the electric pulse to the motor depending on the CV setting to quiet the motor. Most new motors don't have that problem anymore.


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## Mark R. (Jan 26, 2013)

It's actually not the motors that don't have that problem any more, it's the decoders. Older decoders pulsed at a lower frequency that you could actually hear - the original Atlas decoders were noted for this. DCC decoder manufacturers increased the frequency to cure this. It's still there, but the frequency is high enough, the human ear cannot pick it up .... although your dog might think otherwise ! 

Mark.


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