Because DCC decoders control loco speed with Pulse Width Modulation (PWM), locos automatically get pulse power control that generally makes locos run better than they would with normal DC Analog control. However, because these pulses are processor controlled, they can be manipulated beyond that - even made to be erratic, if that's what it takes to make a loco run smooth at slow speeds.

Because of the way electric motors work, and because of the roughness in some drive trains, it usually takes more voltage to get a loco started than to keep it running at a slow speed. Further, when running at low speeds, this motor/drive train "stiction" can make a loco run erratically at slow speeds, at best, and not slow at all at worst. While pulse power somewhat helps with this "stiction", more can be done.

Another problem with PWM is that it can cause a buzzing noise in some locos, especially if the frequency matches the resonance of the loco's shell. The way to overcome this is to increase the PWM frequency to beyond that that the human ear can hear.

When the Pulse Width Modulation frequency is increased to provide Quiet Drive, motor torque is lost. This is a fact of life with electric motors. Most manufacturers don't do anything about it. But Train Control Systems decided to try. What they came up with is Dither. It not only returns the torque where it's needed, but also provides a unique feature that makes locos run smoother and better at slow speeds. Athearn type locos benefit most from this, because they have the most to gain.

Dither is a feature unique to Train Control Systems decoders. It was originally developed to return lost torque due to the increased frequency for Quiet Drive. But the side benefit of overcoming "stiction" of lower quality locos is just as important.

Dither adds a little extra voltage with frequencies different than that of the normal Pulse Width Modulation. What this does is provide some extra bumps of power at irregular times. Because "stiction" can be immune to some frequencies, the addition of a second variable frequency can break it.

Dither is programmed with CVs 56 and 57. Factory default for these two CVs is zero (0), which turns Dither off.

CV56 is used to select a frequency. The range for this CV is 0-255, with 0 (zero) being off. The highest frequency addition of 30 extra pulses per second is obtained with a value of 1. The higher the value, the fewer additional pulses are added. A value of 5 is the recommended starting point, but the optimum value is obtained through experimentation. The practical range is 1 through 10.

CV57 controls the amplitude of the additional pulses. The range for this CV is 0-255, with 0 being off and 255 being the highest voltage pulse. The practical range is about 5 through 50. The recommended starting value for this CV is 25 to 30. The optimum setting is again obtained through experimentation.

Dither's extra voltage bumps is provided only in the lower 1/5 of the speed range, where it's needed. However, it can be used in conjunction with V-Start and/or Kick Start to provide whatever is needed to make most any loco start and run smoothly at any speed. Yes, Train Control Systems makes Kick Start available for use with the built-in speed table.

These three features can provide the power manipulation needed to make almost any loco start and run smoothly at any speed. They cannot, however, compensate for poor electrical conductivity getting to the decoder. For more information, refer to Athearn Improvements.

This feature is provided solely by the decoder. Train Control Systems decoders are the only ones that have this feature. So if you want Dither, you must get a Train Control Systems decoder.

Decoders with Dither will work equally well on any DCC system. Dither is programmed in CVs 56 and 57, so requires a system or method to program those CVs.

All of Digitrax's current systems can program any value into these CVs.