THERE IS NO SUCH THING AS A DIGITAL AERIAL!!!
Sorry to shout but the term "digital aerial" is just a ploy by installers/ suppliers to charge a higher price.
At present freeview digital transmissions are on a much lower power than the analogue transmissions - in my local case it is one hundredth of the power!So firstly one may require a higher gain Aerial to receive digital transmissions particularly if you are some distance from the transmitter,
Secondly in order to avoid interference the digital transmision frequencies (channels) are often significantly diferent to the local analogue channels and are also spread about. So a wider bandwidth aerial is also sometimes necessary
In my local case my aerial is designed to receive Group A as my analogue channels are 21,23,27,31 and (also on reduced power) 39 for C5, Freeview multiplexes are on 41.42.44.45,46, and 67!. With my existing aerial at about 20 miles from the transmitter I get 100% except for C46 at about 50% and C67 at 95%+.
The Weather and how many pigeons are sitting on the aerial does have an effect on C46 and occasionally C67 reception.
So for reception of freeview you may need to install a higher gain/and/or ahigher bandwidth aerial. Such beasties can be purchased for £20-30. Installation should be no more than £50 inc VAT (1 hour)