Umm... I'm posting this for the benefit of the less experienced people reading this. There IS a way to give almost analog power to a stock DC loco on a DCC layout, but the wording of the sentence could be misleading.
The technique is called "pulse stretching", although fewer systems support this... and it is not pure DC, but the DCC signal is changed from the standard symmetric DCC square wave (equal positive and negative pulse widths) to asymmetric, where when going forwards, you make the positive pulse much longer than the negative pulse.
This usually causes extra motor heating, and the operation is noisy.
So you can run an analog loco on a DCC layout PROVIDING you have pulse stretching in your DCC command station.
Also note that when doing this, ONLY one loco on the layout at a time.
NCE discontinued this feature years ago.
Greg
p.s. a DC loco placed on a DCC layout will buzz and not move, different buzzing than buzzing while moving on DCC with pulse stretching, and different again from a "DC" pack with pulse width modulation which can also cause buzzing.