Needs slight fix - Both units are DCC sound the D unit has a speaker that needs to be attached to the soundboard in order to get the sound. The C unit is set up to receive a speaker but does not have one. Both units have the SoundTrax MC-IM84 DCC sound boards installed - see pics The two units run well together in DCC and DC. Super smooth runners with front lights - ditch light, and main headlight.