BEMF can tell the decoder how fast the motor is turning, which
is related by the gears to how fast the wheels are turning.
In diesel sound decoders, the question is which of the 8
notches of the motor sound should be being generated. Simply,
the decoder will divide the speed ranges into 8 parts and assign
a sound to each one.
But a diesel running in, say notch 5, will sound different if it is
pulling hard or if it is running light. Sophisticated sound decod-
ers use user input and BEMF to decide where in the range of
notch 5 sounds it should be.
Some decoders allow the user to manually move through the
notches, for more realistic operation. All seem to come with an
automatic selection process enabled.
Now comes the conundrum of steam locomotives. The chuff
should be directly related to specific mechanical positions on
the loco, either wheel position on rod locos or motor rotation
on geared locos.
12
12: SoundTraxx 810038
chuff cam mounted on
the inside of an HO
steam driver – this is a
cam for an articulated
style of loco with two
sets of cylinders and
drivers.
DCC Impulses Column - 9
MRH-Feb 2013
