Recording XM signals...an issue
Mon, 28 Nov 2005 18:32:46 GMT
My satellite TV service is now supplying XM sound. Sounds "pretty"
good for most pop music and some classical, except for opera. My
intent is to see whether it makes sense to subscribe to the service
directly. Here's the scenario.
I record the XM sound...opera... on my PC, but when I replay it , it
sounds like hell. I am pretty picky....I can sometimes pick up on
differences between ripping or sampling at 256K vs. 320Kb. A local FM
XM and Sirius have been getting careful scrutiny from a
group of experienced audio engineers I'll refer to as "The
Detroit Audio Mafia" ever since they first came out. These
guys have been listening to XM and Sirius since the only
receivers around were prototypes for the big 3 auto makers
to try out.
After all, this *is* Detroit and the reason XM and Sirius
exist primarily for listening in cars.
"The word" on the street in Detroit from "The Detroit Audio
Mafia" is that the sound quality of XM and Sirius has been
flushed down the porcelain convenience, as more and more
concurrent services were added.
This makes perfect sense, of course. As the bitrate per
service goes down, the sound quality *must* go down.
At this time XM and Sirius are generally agreed-upon by "The
Detroit Audio Mafia" to be generally *unacceptable* for
serious listening, even in a moving car.
XM and Sirius weren't always this way, but that was then and
this is now.
station does an excellent job with classical...comparison of ripped
tracks vs recorded tracks just doesn't show any deviations to my ear.
But, these XM broadcast for inherently high dynamic range music like
opera are a true litmus test.
When I use a small utility from Nero...WaveEditor...I can see the
frequency and amplitude of the recorded sound. Pretty funky compared
to CD sound....clipped signals and frequency truncations and
artificial boost at higher frequencies. Plays havoc with opera. Other
stuff seems to "sound" reasonable...who can tell with the Stones???
Went to AOL/XM streams and recorded some opera at my dialup speed of
44kb...damned slow but these new compression algorithms are amazing.
The sound was still not good enough to capture classical, especially
opera, but looking at the signals showed that the signals were not as
garbaged up as those from my satellite TV source. Stands to reason
that some extra truncations, compressions, and filtering are occurring
on the satellite beam.
Now, here's the issue: if the XM or Sirius signals are that
manipulated when directly transmitted, then, again, the opera is
likely to be the most damaged. I don't want to spend the time or money
on the service and hardware unless I am truly getting CD quality
There is a wrinkle. My satellite TV has a small amount of
objectionable ghosting...three or more very small ghosts... that they
cannot figure out...I think its back or forward refelction/deflections
from a nearby tree that is ... for all practical
purposes...interferring with the clear line of sight to the satellite.
If it is in the video, it may be in the audio, too, but I don't have a
way of sampling the video.
Anybody have some experience they could share?? On any aspect of this
series of experiments??
Is this a digital satellite service? Ghosting is not possible with
digital, so I presume it is analogue, although I thought all new users
were digital - oh well.
No, it can't produce ghosts - there simply isn't a mechanism. What
does happen, though, particularly on channels that are starved of
bandwidth is that artificial edge-sharpening techniques are sued that
produce a sort of nasty white outline to picture features. I suppose
these might be construed as ghosts.
HDTV is producing some huge problems of its own. Having to compress a
pretty huge original stream into a normal channel makes for some
pretty horrid MPEG artifacts at times. I'm not saying that the picture
would necessarily look better at standard definitions, but that is
certainly the case on occasions.
Sorry that last sentence should read way BELOW.
The source of the ghost image can be estimated by measuring how far
across the screen from the original image it is. I have to say,
though, that ghosting with satellite is unusual because the dish beam
is so narrow. If you are on a communal distribution system, it is more
likely to be reflections from unterminated cable runs. Talk to the
installer about this.