Digital TV

Not sure if I have the proper group, but I'll give this a shot.

I now use an outdoor antenna.  Some channels come in perfect and some 
not too great and some really bad.  Will the DAC (digital to analog 
converter) make poor signals come in better, worse, or the same?

When cell phones went digital it was said that calls will come in 
clearer, but they will also give less warning when in an area with poor 
reception, they basically go from good to dead.

Thanks,
Tony