XM compression / bit rate / comme - AVS Forum
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post #1 of 12 Old 07-09-2003, 07:23 PM - Thread Starter
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Hello,

What is the bit rate for XM? If it's more than
192kbps I think XM is not getting the most
out of its signal.

To me, minidisc ATRAC (384kbps) or minidisc
ATRAC LP2 (192kbps) sounds better than XM.

Having said that, I enjoy the XM *service*. The
programming is varied, with lots of surprises
thrown in. XM30 was broadcasting surf
instrumentals -- find *that* on commercial radio.
I hope they can get the sound worked out as
the technology (hopefully) gets better.

Does the Delphi Sky-Fi have the ability to
have its firmware updated remotely as
compression techniques get better?

Is there any possiblity that Delphi will produce
a "pocket Sky-Fi" for headphone listening?

Best regards,

Paul Bigelow
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post #2 of 12 Old 07-10-2003, 07:26 AM
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XM has total bandwith of about 6 megabits for 100+ channels and a bunch of overhead issues. The bitrate is variable by channel and content. Looking at some old tech articles, there was a cap of 64kbs per channel, though I don't know if that has been lifted. Given the quality of sound, I think they are getting their money's worth.

The scary thing is XM seems to believe that if (when?) they get better compression algorithms they will use them to add channels rather than uping the quality. I would be very unhappy if they did this.
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post #3 of 12 Old 07-10-2003, 08:29 AM
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XM's digital audio coding is fairly spiffy:

http://www.xmradio.com/newsroom/scre...002_04_18.html

HiDefDave
 

WPTV/WFLX West Palm Beach, FL

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post #4 of 12 Old 07-10-2003, 11:57 AM - Thread Starter
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Hello,

"Delivers sound remarkably close to Compact Disc"

That's my problem with the sound. To me, it isn't remarkably close.

Well behaving FM stations sound better.
Well mastered records with clean pressings sound better.
Minidisc sounds better.
Minidisc LP2 sounds better.
CD's sound better.

All the above have defects but, my goodness, XM is full of them.

Granted, the technology is complex. It's amazing that anything intelligible
is received at all. I just think that with all the money and technology behind
this this thing that it's a shame that they risk torpedoing it all by having to
reduce music to such a low bit rate that the music is being severely
damaged, if not destroyed.

Who has listened to XM with headphones and compared familiar songs
with CD versions? I have. To me, the difference is immediate and
obvious -- XM is clearly inferior.

I'm hoping that as the service and technology matures that sonic quality
will improve or XM will realize that, maybe, 100 channels is not necessary
and sacrifice half to double the per channel bit rate.

Despite these grumblings I still intend to keep it. It makes for some
interesting and varied background music. It just could be so much more.

<on soapbox -- off topic>

In thinking about XM a bit could XM be a Trojan Horse? An unintentional
Trojan Horse, maybe? It has been stated that Clear Channel
Communications is a shareholder. As Clear Channel marches onward
assimilating broadcast stations in its path, consolodates DJs, and
standardizes programming in an apparent goal to become a national radio
network, it would seem logical that Clear Channel would be interested in
XM which could either be it's greatest threat or, if XM *really* takes off, its
greatest conquest in a corporate takeover -- a national radio station in one
swoop. Then, all that wonderful programming may just go out the window.

Maybe just I'm being paranoid. It is certainly off topic about the sound
quality.

<off soapbox>

Best regards,

Paul Bigelow
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post #5 of 12 Old 07-11-2003, 02:48 PM
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Well, if I spent any time listening to XM with headphones, I suppose I'd be concerned about their lossy coding system's shortcomings. I spend 90% of my listening in my car and the rest either on a highend audio system in my HDTV media room or on a boombox on the patio (Sony plug 'n play unit).

On my big rig I hear funny stuff but I don't let it ruin my day. I mostly use it for background, anyway. In the car and outdoors I can't hear any problems because they are swamped by ambient noise.

Yes, the very best sounding FM stations, the ones with minimal processing like many public radio stations sound better than XM. But XM has found a programming niche with better than average audio quality for a broadcast medium.

I'm saving up for a universal CD/SACD/DVD-Audio player for ultimate sound quality.

HiDefDave
 

WPTV/WFLX West Palm Beach, FL

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post #6 of 12 Old 07-13-2003, 04:16 PM
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XM and Sirius each have 12.5 MHz of spectrum, but the way they use their spectrum does vary a little bit. XM uses two seperate transponders per satellite, Sirius only one.

It comes up to around 3 to 3.5 Mbps.

Sterling
Moderator at SiriusBackstage.com
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post #7 of 12 Old 07-14-2003, 11:00 PM
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Clear Channel's influence on XM is negligible. They get one board member and for now are entitled to make XM carry one of their crappy CHR stations. And Clear Channel just hedged away their XM shares with Bear Stearns, anyway.

It would be virtually impossible for Clear Channel, or anyone else, to take over out XM at this stage.

And I've yet to hear an FM station that sounds close to XM. Is XM going to sound like DVD-A through $10,000,000 mono-blocks in your secret volcano lair? No. But it's damn good.
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post #8 of 12 Old 07-16-2003, 11:46 AM - Thread Starter
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Hello,

A "well behaving" FM station (there are some) through a Sangean pocket
radio (try the DT-110) with sony MDR-EX71LP earplugs sounds better than
the Delphi home unit with the same earplugs used in the variable line out.
Don't need $10,000,000 monoblocs or DVD-A or SACD to get better quality
sound than XM.

Just to be certain, I've plugged the Sky-Fi into a real, yet "nothing special"
amp and have heard the same weird artifacts on the vocals.

The defects are not subjective. They're factual. Maybe some people can't
perceive it or don't care but the defects are still there.

No doubt, the service and music selection is superior. Beats most
local stations by *ten* miles. For some, that's good enough. Heck,
I listen to certain AM stations because of the music selection.
One of those stations is even Motorola C-QUAM AM stereo. Does
AM sound perfect? Nope, but it doesn't advertise as being "remarkably
close to Compact Disc", either.

I just hope that XM works on improving the quality of sound. If that
means eliminating some channels then so be it.
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post #9 of 12 Old 08-05-2003, 11:28 AM
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I definitely hear the dithering on vocals, cymbals, saxophones, horns, etc... Mostly highs. I seem to notice it a lot on jazz. It's definitely good enough for car audio. The main draw for me is the content. I've been a hi-def music consumer for a while now, and all the quality in the world won't do you any good if you don't have any content. XM has that in droves. I think the negative press Clear Channel has been gettng recently with these media ownership hearings will come in handy if they make a play for XM. Hopefully any such advances will be blocked due to antitrust concerns.


Ron
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post #10 of 12 Old 08-05-2003, 03:03 PM
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XM clearly is not CD quality, both in my car and home I hear noticible differences - very easy to tell. I have emailed them asking for more quality. For the home, part of the problem may be inferior D/A's Hard to imagine these small dual function receivers like SKYFI have good components.
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post #11 of 12 Old 08-05-2003, 03:59 PM
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"Asking for more quality" is not going to get you better quality.
XM and Sirius both have limited spectrum resources for audio, they can not get more bandwidth unless the FCC allocates additional spectrum to them. And if their satellites and receivers can even handle additional spectrum.

Right now its as good as its gonna get for a long, long while.

Sterling
Moderator at SiriusBackstage.com
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post #12 of 12 Old 08-05-2003, 06:50 PM
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Quote:
Originally posted by BuggyBoyCA
"Asking for more quality" is not going to get you better quality.
I don't think it will get more quality, but it may help us keep from getting worse quality. I know XM is actively thinking about adding more channels and giving us less bandwith / channel. The more customers that tell them quality is more important than a few extra channels, the less likely they are to do that.
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