16 May
2007
16 May
'07
7:52 a.m.
Ken Restivo wrote:
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I've noticed a nasty aliasing noise when connecting an analog output
from a digital source, to the analog input of another digital device.
For example, going out of a cheap soundcard on a PC, into a nice (or
cheap) A-D converter, an ugly high-pitched aliasing noise appears
even with no program data. It's not audible to my ears when listening
just to the analog output of the hda-intel; one must plug its output
into an A-D in order to hear it, and then it's rather loud.
I've noticed this with my expensive Edirol firewire interface and
with my cheap Audiophile USB interface. The common factor is when the
sound being digitized comes from an ugly hda-intel sound chip. All
three are running 48khz
Would this happen even with expensive D-A's? Is this a common
problem when connecting D-A back to A-D?
I'm asking because I'm going to have to plug the analog outs from one
of these interfaces (the firewire or the USB, not the hda-intel) into
someone's PresonusFirebox/ProTools rig on Friday, and I want to know
if I'm going to have to deal with this aliasing noise.
I don't think this
is aliasing noise since the HDA will have some sort
of reconstruction filter, and the Edirol/MA-Audio interface will have a
decent anti-aliasing filter.
It will probably have to do with the power supply noise rejection of the
codec attached to the HDA chip. Or the headphone amp that is definitely
present in it. The load presented by a headphone (can be as low as
32ohm) is different from the load presented by a device input (multiple
kiloohms). This can cause a change in PSSR behavior. It's related to
ground-loop type of behavior. (if you can make the sound change by e.g.
moving the mouse or changing the stuff displayed on the screen, most
likely you're seeing bad PSSR. The sound comes from the dc-dc converters
from the LCD panel).
Most likely you won't be experiencing this when connecting the edirol to
the presonus device. The only way to find out is to try it. Be sure to
use balanced cables.
He runs at 96Khz, IIRC. I dunno if that will make the noise better,
or worse. It'd be nice to go S/PDIF out, but I don't know if that'll
work either, if the sample rates don't match.
It only works if the samplerates
are the same and the two cards are
sync'ed. Analog will be easier.
Pieter