[mythtvnz] Audio question and video pixelation question

[Paulgir]

I've been getting familiar with operating my mythbox.I don't appear to  
have any major
problems,but I do have a couple of questions the list members may be able  
to
help with.

1. When watching live TV or recordings,the audio seems to default to  
English AC3 5.1 ch
(I get that message briefly when I select a new channel).I can select  
English
AAC-LATM 2 ch with the <-> key.I can actually  also select Italian  
AAC-LATM 2CH
on some channels although this is in English too.
The AAC-LATM sounds better through my sound system - correct level,full  
stereo.
AC3 5.1 ch doesn't come through well.

Is there somewhere I can set the default to English AAC-LATM?

2. I get brief periods (up to 30 secs) where the video gets progressively  
more pixelated
and distorted,sometimes freezing,sometimes associated with audio  
distortion.
I suspect this is due to poor signal (DVB-T) as I am 55km from the  
transmitter.
signal strength is usually around 80% to 95%
I'm planning to put up a hi gain antenna.

Are there any other causes I should investigate?