http://www.technicalwhizz.com.au/html/digital_tv.html
"I Have Digital TV But My Pictures Freeze, or Blocks Appear and Sound Stops and Starts. Why?"
These are classic symptoms of a problem receiving the digital signal to your TV. There can be a range of possibilities causing these symptom here are a few.
Antenna problems; such as it is not digital compatible, corroded, or not strong enough
Cable problems; aged cable, kinks, not shielded correctly, cable to long
Faulty wall plates, or not digital compatible leads behind the TV,
Poor quality Digital set top box or TV.
If you don’t live in the main cities it can be unlikely a digital box under $80 will work well on all channels.
We can rectify any digital problems you have from recabling, installing an antenna or providing a digital set top box to installing a fully featured Digital Television.