Digital broadcast can sent quality, but can also sent decreased quality for technical or economic reasons.
A decreased video resolution, a limited video bitrate, a too low audio bitrate, multiplexs with too many channels in it due to broadcast economy, many things to verify.
On this website, find quality measurment of TV and Radio broadcast, and find on which support the quality is the best.
For this, are checked : video resolution, average and maximum bitrate, bitrate type variable or CBR for Video, Bitrate and type for Audio .
Other explanation pages on this site:
MPEG : Picture resolution
MPEG : Artefacts
MPEG : Noise reduction
MPEG : Statistic Multiplexing (VBR/CBR)
MPEG : Group of pictures (GOP)