[mythtv-users] Re: Does MythTV Obviate a DVD Player?

Ben Buxton mythtv at ml.cactii.net
Mon Sep 6 06:30:37 EDT 2004

Hamish Moffatt <hamish at cloud.net.au> uttered the following thing:
> On Sat, Sep 04, 2004 at 06:13:11PM -0400, Jay R. Ashworth wrote:
> > On Sat, Sep 04, 2004 at 10:59:42PM +1000, Hamish Moffatt wrote:
> > > > blind bit of difference. The one thing I'd say is use optical cable if 
> > > > possible to avoid any electrical hum.
> > > 
> > > How will you hear electrical hum on a digital signal?
> > 
> > Because low frequency AC hum on a cable carrying an analog
> > representation of a digital signal can mess up the line receivers and
> > cause bit and packet errors.  No signal is *entirely* digital, though
> > optical signals likely come closest.

Hamish's ground loop issue is definitely a valid concern - ground loops
through the amplifier and PC earthing will be heard _as hum_, regardless of
whether the cable is digital. Google for ground loop and you'll see that
this is not the usual silly pseudo-audiophile tripe, but a problem when
the analog section of an amplifier has more than one path to ground.

Just as long as you don't believe the crap that some people have who
claim optical cables can sound different (excluding length limitations).

> Alright, that's a fair explanation. You could get bit errors. That won't
> be heard as electrical hum, which was my original point.

Generally bit errors will be heard not as a reduction in clarity of the
sound, or even 'muddiness'. Instead, you will _know_ you will have bit
errors as you will hear awful crackling in the output, at all signal
levels. That's the nice thing about digital...if it sounds clean, it is
clean. If it isnt clean, it will sound _awful_.

I have a 12 metre cheap ($1/metre) cable for my digital output, running
past a microwave and a fridge. But I get zero errors and perfect

> More accurately you would prefer optical to avoid ground loops.
> Electrical hum is the analog result of ground loops.
> Hamish

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