[mythtv-users] Problems with alsa & spdif & myth
myth at dgreaves.com
Wed Apr 7 15:07:50 EDT 2004
John Sturgeon wrote:
> I'm completely baffled. Where is the noise/hum coming from? This is
> a completely digital signal. The amplifier does not touch the signal
> until it is decoded. Any 'static', or 'noise' introduced by using a
> wire instead of fiber optics would *never* be heard by the amplifier
> because it is not an audio input. The 1's and 0's either get there,
> or don't.
Take a look at
or just Google for ground loops.
It doesn't come from the signal.
It comes from the electrical conductivity afforded by a metallic link -
ie a non-optical SPDIF cable.
The real world isn't digital :)
> Sharp bass? Not possible.
A thundercrack is a sharp bass noise.
A thunder roll isn't.
Basically good 'attack' makes it sharp.
If you do a fourier transform on a low frequency (actually it's not
frequency, it's periodicity but we won't get into that here!) signal
you'll find that they contain a variety of signals. The classic example
is a true square wave that contains all other frequencies (hence is not
possible to achieve in nature). The less well reproduced all these
frequencies are when you play back the signal, the worse the sound.
Typically this happens in cheap car stereos with woolly bass lines - the
amps just can't pull the speaker cones back and forth sharply enough.
I can hear this effect when I swap cables - come and listen next time
you're in the south of the UK if you like :)
I don't *know* *why* it happens? digital corruption, ground loop effect?
poor electrical/optical conversion? I dunno.
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