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fwiw quick and dirty: twisted pairs is for NOT TRANSMITTING EMR as the twists effectively cancel any fields generated in the wires. kinda sorta works on receiving except for really high frequencies where the waveform can exist at some even multiple of the twist length ( say a couple of ghz). Sheilding is for NOT Receiving EMR. If you want to go really nuts, twisted pairs and sheilding. Ferrite is kinda both, they act like inductor cores for low values of EMR effectively stopping the ac component (2*pi*f*L {in Henries}) with reactance. Your PWM signal is basically a dc voltage so...... ferrite doesn't bother it much below a KHZ or two as the reactance is so small at those fequencies. If you need to go really high Freq, then you need co-ax cable, but that is a weird deal all its own with skin effects andthe like.
pretty much if you want to stop receipt of EMR, then sheilding on the pairs, then the bundle sheilded with a foil or a braid and tied to different GROUNDS (not negative battery) at one end only.
Not an instrumentation super, but instrumentation Tech at Edwards AFB rocket site thruster test lab.
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