Is there an area on the XM website that tells us if the music is CD quality

what bandwidth is XM broadcasting music at

Hi Raven,

XM used to broadcast "near" CD quality in the early days.....

Ekeefe has a nice explanation:

quote:

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Originally posted by ekeefe:


Hello,

This information is not from XM, just a way to look at the bandwidth use of XM in my opinion.

The XM signal uses 12.5 MHz of the S band from 2332.5 to 2345.0 MHz. The XM signal can support a maximum of 255 channels. If each of the channels was broadcasting at full chip set bandwidth, 64kbps, the system would only allow for 195 channels. This means for XM to fully utilize the channels some must be lower in bandwidth. Here is some of the bandwidth allocations on XM.

There are the low bandwidth traffic channels. I'm not sure of the data rate but it is low.

Each OEM gets a little bit of the available bandwidth. 128kbps of bandwidth is used for GM's On Star system.

The XM-WX weather service operates sort of like teletext does. You ask for a resource and then wait for it to come around in the data stream rotation. The service will also, in the software provided with the weather receiver, let you select the data feeds you always use and it watches for them and caches the data off for later use. XM-WX also uses some bandwidth. Once again, I'm not sure of the data rate for this service, but I would be surprised if it uses more than 1 channels worth. The system only sends raw text and binary feeds to the receiver. The software on the computer connected actually generates the images you see.

The Nav-Traffic service also uses some bandwidth. Like the weather service, I'm sure this uses 1 channel for the entire service. The maps are generated in the head unit using raw traffic data that is overlaid on a GPS generated map.

As for the 5.1 surround channels that are coming online soon, they will work similar to the way Dolby pro-logic worked on VHS tapes. Only 2 channels are required and carry a matrix signal that is decoded into 6 different audio channels. Pro-logic was only 4 channels (Left, Right, Center and Rear). The codecs used today have better compression and this allows for more data to fit in the same sized data stream.

People on the site have been discussing the reduction in bandwidth of some channels. The numbers they are discussing are 32 - 48kbps. At these rates the amount of bandwidth used would be as follows:

32kbps - 8.16 MHz for 255 channels
40kbps - 10.2 MHz for 255 channels
48kbps - 12.2 MHz for 255 channels

Since the system has a maximum of 255 channels with some at full bandwidth and some (Traffic, Emergency, some Talk and maybe some of the data services) at lower bandwidths, the system can easily fit new channels.

I think the bandwidth reductions on some channels is a 'Test the waters' sort of thing. If people don't complain about the quality, if they even notice in some cases, that leaves bandwidth free for other uses for XM.

This is just thoughts on my part and not some sort of official, I got a secret, sort of information.

Hope you found this interesting,

ED

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quote:

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Originally posted by DesertRat:

quote:

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Originally posted by espnjason:
DR, how is a channel scan conducted?
I am curious of what the bitrate is for all the non-music channels on XM.

And is there anyway I could do it for my own research?

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Anyone with one of the original XM2go radio can measure the period it takes to fill its memory when in record mode. This isn't all that practical if you want to characterize all the channels. A 32kbps channel will require almost 9 hours of record time.

The technique I use requires a hardware hack. Basically I to tap into clock and strobe lines within the receiver. A few gates and a counter allow a direct bitrate readout on a frequency counter. Any channel can be measured within seconds. The encoding rates for the accPlus encoded channels are based on multiples of 8,192 (2^13). The AMBE channels run at 4,096bps. Because of the way XM allocates fixed blocks of bandwidth, they don't appear to use VBR encoding.

To my ears, 48kbps (49.152kbps) is the sweet spot for aacPlus. I've always thought it was reasonably close to a clean FM signal. Good high-end details and excellent stereo imaging. I found the level of encoding artifacts to be acceptable. Not perfect, but pretty good for that low of bitrate.

At 40kbps the upper mid-range and high-end frequencies become noticeably degraded. The higher frequencies sound muted and indistinct. It also appears the effective dynamics are crushed. Without high levels of pre-processing, much of the details drop out. This was really noticeable last year when Cinemagic was reduced to 40kbps. They do manage maintain something of a stereo image, but little or nothing in the SBR frequencies.

Music encoded at 32kbps has a bit less high end content than at 40kbps. It does however sound worse to me than than the small differences indicated on spectral plots. The big drawback of 32kbps encoding is the decimation of the stereo image. What remains has limited channel separation and can be transitory in nature. It's a shame XM has reduced the majority of their music channels to this abysmal quality.

I've sampled accPlus v2 where the primary improvement is the addition of Parametric Stereo. About all PS manages to accomplish is to marginally improve the stereo imaging of 32kbps encoded music. It's nothing to get all that excited about.

As for the bitrates on all the channels, this is from the last sample. Missing is 201, the new SEC play by play channel. For whatever dumb reason, it currently appears to be running at 16kbps.

code:

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       Low Transponder                   High Transponder
  1 XM Preview        16,384     75 Hear Music           40,960
  4 The 40s           24,576     76 Fine Tuning          65,536
  5 The 50s           32,768     77 Audio Visions        40,960
  6 The 60s           32,768     78 Escape               40,960
  7 The 70s           40,960     80 The Move             32,768
  8 The 80s           40,960     81 BPM                  32,768
  9 The 90s           40,960     82 The System           32,768
 10 America           40,960     83 Chrome               32,768
 11 Nashville! cm     49,152     84 XM Chill             32,768
 12 X Country         40,960     90 Fuego sp             32,768
 13 Willie's Place    32,768     91 Viva sp              32,768
 14 Bluegrass Juncti  32,768     92 Aguila sp            32,768
 15 Folk Village      40,960     94 Caliente sp          32,768
 16 Highway 16        40,960    100 Air Musique fr       32,768
 17 US Country        40,960    101 The Joint            32,768
 20 Top 20 on 20      40,960    102 Sur La Route fr      32,768
 21 KISS cm           49,152    110 XM Classics          57,344
 22 MIX cm            49,152    112 Vox!                 57,344
 23 The Heart         40,960    113 XM Pops              65,536
 24 Sunny cm          49,152    115 Radio Disney         32,768
 25 The Blend         40,960    116 XM Kids              32,768
 26 Flight 26         40,960    121 Fox News             16,384
 27 Cinemagic         40,960    122 CNN                  16,384
 28 On Broadway       40,960    123 CNN HDLN             16,384
 29 U-POP             32,768    124 ABC News & Talk      16,384
 30 XM Hitlist        40,960    125 Weather Channel      16,384
 32 The Message       32,768    126 CNN en espanol       16,384
 33 Spirit            32,768    127 CNBC                 16,384
 34 enLighten         32,768    129 Bloomberg News       16,384    4,096
 40 Deep Tracks       40,960    131 BBC World Svc        16,384
 41 xL Bone Yard      32,768    132 C-Span Radio         16,384
 42 xL XMLM           32,768    133 XM Public Radio      32,768
 43 XMU               32,768    140 ESPN Radio           16,384
 44 Fred              32,768    141 ESPNEWS              16,384
 45 XM Cafe           40,960    142 Fox Sports Radio     24,576
 46 Top Tracks        40,960    144 XM Sports Nation     16,384
 47 Ethel             32,768    145 IndyCar Racing        4,096   16,384
 48 xL SquiZZ         32,768    146 PGA TOUR Network      4,096   16,384
 49 Big Tracks        40,960    147 XM Deportivo sp      16,384
 50 The Loft          40,960    150 xL XM COMEDY         24,576
 52 The Verge         32,768    151 Laugh USA            16,384
 53 xL Fungus         32,768    152 EXTREME XM           16,384
 54 Lucy              32,768    153 xL Laugh Attack      16,384
 60 Soul Street       32,768    154 National Lampoon     16,384
 62 Suite 62          32,768    155 Take 5               16,384
 64 The Groove        32,768    156 Oprah & Friends      24,576
 65 xL The Rhyme      32,768    161 WSIX cm              40,960
 66 xL RAW            32,768    162 E!                   16,384
 67 The City          32,768    163 Sonic Theater        16,384
 68 The Heat          32,768    164 Old Time Radio       16,384
 70 Real Jazz         40,960    165 Talk Radio           24,576
 71 Watercolors       40,960    166 America Right        24,576
 72 Beyond Jazz       40,960    167 Air America          16,384
 73 High Standards    32,768    168 Fox News Talk        16,384
 74 Bluesville        32,768    169 THE POWER            16,384
174 Sports Guide           0    170 FAMILYTALK           16,384
247 Emergency Alert    4,096    171 Open Road            24,576
                   ---------    172 Sport Plus fr        16,384
   Primary Payload 2,035,712    173 WLW 700              24,576
                                175 MLB Home Plate       16,384
                                176-190 MLB pbp x 14    229,376   16,384
                                190 MLB en Espanol        4,096   16,384
                                191-199 College pbp x 9  36,864  147,456
                                200 XM Live               4,096   32,768
                                202 xL the ViRUS         32,768
                                204 Home Ice             16,384
                                205-209 NHL pbp x 5      81,920   16,384
                                210 Boston                4,096
                                211 New York City         4,096
                                212 Philadelphia          4,096
                                213 Baltimore             4,096
                                214 Washington DC         4,096
                                215 Pittsburgh            4,096
                                216 Detroit               4,096
                                217 Chicago               4,096
                                218 St Louis              4,096
                                219 Minneapolis           4,096
                                220 Seattle               4,096
                                221 San Fancsico          4,096
                                222 Los Angeles           4,096
                                223 San Diego             4,096
                                224 Phoenix               4,096
                                225 Dallas/Ft Worth       4,096
                                226 Houston               4,096
                                227 Atlanta               4,096
                                228 Tampa                 4,096
                                229 Orlando               4,096
                                230 Miami                 4,096
                                244 Canada 360            4,096
                                245 Quoi De Neuf fr       4,096
                                                      ---------
                                      Primary Payload 2,039,808

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Originally posted by wxray:
Not that I know of. All I know is it sounds about as bad as I ever remember it. I am more unhappy about that than anything else.

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_________________
Beyond AM, Beyond FM...

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Originally posted by farketyfark:
I'm not trying to be a Sirius fanboy, but...(posted 10/24/06)

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To make room for the new channels, XM has demoted all of their 40kbps streams to 32kbps. I noticed this last week when the stereo image all but disappeared on some of my favorite channels such as Real Jazz, Deep Tracks and Cinemagic. None of XM's 40kbps channels were spared, only the Clear Channel ones remain. Both the French music channels joined the "40s" as 24kbps mono music streams as did XMPR.

As of 10/05:
64kbps: Fine Tuning, XM Pops
57kbps: XM Classics, Vox!
48kbps: KISS, MIX
40kbps: Nashville!, Pink, Rock@Random
32kbps (music): Everything else except the 24kbs channels
32kbps (talk): the Virus, Howard 100,101 ??
24kbps (music): 40s, Air Musique, Sur La Route
24kbps (talk): XMPR, Fox Sports Radio, XM Comedy, Extreme XM, Oprah & Friends, Reach MD, Americs's Talk, Talk Radio, Open Road, WLW
16kbps: Preview channel; Remaining News, sports and talk; MLB channel marker
4kbps: Traffic, XM Scoreboard, Canada 360, Quoi De Neuf, Cal Sportif, Emergency Alert, channel markers

Bad move. Especially to make room for lousy programming like Howard Stern.

For me, the merger has not had a single positive effect, and the negatives are starting to pile up.

As an internet radio broadcaster, 48kbps is quit unacceptable. 64kbps is FM quality...128kbps is CD quality.

I too am a XM subscriber and constantly get annoyed with the the channels using quite a low amount of bandwidth while listening. I can only listen to the music channels for so often before the horrible sound quality gets to me. The talk stations sound alright.

I have no idea how they compress their audio, but I think they could do a much better job if they considered using another method (such as ACC+, etc.)

I agree that the audio quality is now noticeably worse. Honestly, with the lack of highs, there really is now an "AM" quality to the sound. Like many things, you do get used to it, but the poor sound quality really hits you when you switch to something else, such as a CD or terrestrial FM.

But the people who want to pay for Howard Stern can have him. Seems like they're hurting a lot of people for the benefit of not very many.