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Old 8th October 2004, 02:21 PM   #1
Coolin is offline Coolin  Netherlands
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Default Digital format used for satelitte RADIO?

Does anyone know the digital format used for satelitte RADIO transmission (europe)? (it might be the same as the US)

I'm wondering how the quality is compared to CD.

I believe with video it is mpeg2 and the audio compression can be chosen.

Thanks, Coolin
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Old 11th October 2004, 06:51 PM   #2
Coolin is offline Coolin  Netherlands
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Old 11th October 2004, 07:44 PM   #3
brianuk is offline brianuk  United Kingdom
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Im not totally sure but it maybe mp2 for audio as well.
The reason being processing is less (and quality a little too) than withg mp3 so they keep chip power down therefore costs.

I dont have a satellite box, I have terestrial digital, its ok quality, not CD though and as for DAB - thats rubbish! in the uk anyway, maybe better elsewhere.

It all comes down to bandwidth in the end.

Scroll down this page, it gives you a lot of details ...

http://www.digitalradiotech.co.uk/

Hope that helps,
Brian
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Old 11th October 2004, 08:22 PM   #4
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IIRC, its a version on AAC. Basic rate for music channels is 64kb/s.
Voice channels are less.

Nowhere near CD quality. I guess if you want the variety, you'll put up with the audio quality.

Ooops!

Sorry. wrong continent.
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Old 11th October 2004, 08:36 PM   #5
jwb is offline jwb  United States
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If you want to experiment with satellite radio, get the XM PCR and take it apart. You can get datasheets, at least skeletal ones, for all the parts. IIRC the format used is MPEG, and the decoder is in hardware.

The method it uses to demux and decode the channels is pretty baroque, and fun to experiment with. You can also use the I2C bus to fool with the internals of the chip. If you're careful you might be able to mess around with the subscriber "security", although you didn't hear that from me.
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Old 12th October 2004, 11:01 AM   #6
Coolin is offline Coolin  Netherlands
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Thanks for the info guys,

Reading the article satellite is the has the highest bitrates of the the different formats (DAB/ freeview) Most are 128-192 kbps MP2 format.
Also the UK is using the least bandwidth to get more channels (DAB)

Ive been wondering because im pretty impressed of the quality of some of the radio stations. Some are pretty close to CD. I have not done a direct comparison yet as its hard to know what song there going to play

I'm using digital out on my reciever so the quality of the reciever is less of an issue.

Thanks, Coolin
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Old 18th October 2004, 05:47 PM   #7
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With XM radio in the US, I am almost certain it's some AAC variant. Thing is, it's not really easy to pull the decrypted audio from the stream. On a sony DRN-XM01 or a Pioneer GEX-FM903XM, the source decoder (STA450) has serial audio output on 4 pins and S/PDIF output on pin 78. The output format can be configured to the popular formats, Left Justified, I2S, etc. S/PDIF output is PCM of course, I believe with the copy protection bit set. S/PDIF output has to be turned on with the PCM_CONF register of the STA450, and some receivers don't have it turned on. The XM PCR, commander, skyfi, and roady, and second generation sony all have S/PDIF output turned off, so a digital audio transmitter like the DIT4096 has to be used for S/PDIF output.

XM radio uses 3 ICs from ST Micro (well, old receivers anyway, new ones use a newer IC from ST) which includes a CAP, or Conditional Access Processor (It's the ST19AF08 SO-20 IC. It's an 8 bit smart card MCU from ST's line of the ST19 smart card MCU family. Any h4x0r1ng is done with this guy, but no one has been able to find any info yet. :P), the Source Decoder(STA450) and Channel Decoder(STA400). The Channel Decoder is what does the decoding and decrypting of the XM stream. It's output is serial audio or S/PDIF. The CAP is connected to this IC via master i2c bus. Only the CAP and Source Decoder are connected to this bus. (I've made logs of this bus when there was actual traffic. :P) The Channel decoder is what does the demodulating of the datastream from it's carrier. Modulation schemes used are QPSK and COFDM. The STA400 has two IF inputs from the tuner. These are the satellite and terrestrial IF signals. These get demodulated and broken down into a bunch of packets consisting of a 432ms frame. This frame contains encrypted audio data, channel data, program data, etc, broken down into packets, that output from what ST calls a PC bitstream interface. It consists of a data line, clock line, and frame sync line. Data is clocked in at high speed, and the frame sync line indicates a transmission of a 432ms frame. This is input to the STA450 for decoding. The STA450 can output this raw data, minus the frame sync pulse, on it's data output port, turned on and off with a DP_EN pin. Output burst rate is configurable, default is 2MHz.

ST Micro is the only one who makes ICs for XM receivers. You cannot get them without signing an NDA and paying lots of money for a license.

ST has recently combined the Source and Channel decoder all in one package. This is the STA850. The new Roady 2 and SkyFi2 contain these ICs, with the same ST19AF08 CAP. It uses less power and generates much less heat, but the datasheet is nowhere to be found on ST's site. S/PDIF pin is unknown atm.

In my opinion, XM radio has poor quality, but probably better than european DAB. It is no where near CD quality, but sounds decent. XM has a lot of choices, but crappy quality. It's a cool service though, and a great toy to play around with.
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Old 18th October 2004, 06:34 PM   #8
squadra is offline squadra  Netherlands
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Quote:
Originally posted by Coolin
Thanks for the info guys,

Reading the article satellite is the has the highest bitrates of the the different formats (DAB/ freeview) Most are 128-192 kbps MP2 format.
Also the UK is using the least bandwidth to get more channels (DAB)

Ive been wondering because im pretty impressed of the quality of some of the radio stations. Some are pretty close to CD. I have not done a direct comparison yet as its hard to know what song there going to play

I'm using digital out on my reciever so the quality of the reciever is less of an issue.

Thanks, Coolin
I'm impressed to, having connected the spdif output of my satellite receiver to my dac.

The DAC shows 48kHz sample rate, and the DBV standard specifies mpeg 1 layer 2, but i can't find the bitrate anywhere.
The best sound quality was Paris Jazz but that has been replaced by some jazz station from Lyon which seems to 'clip'.
My setup receives Astra 1, Astra 2 & Hotbird.
What is the best station you have found?
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Old 19th October 2004, 06:13 AM   #9
Coolin is offline Coolin  Netherlands
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I can see youve done alot of investigation already A bit over my head...Well im not listening to XM radio nor DAB.
I can record it straight to the harddisk in my reciever so no problems decoding. I havent noticed any lesser quality by recording. It takes up alot of space too, something like 5-10 mb / min so compareable to raw 44/16. The only problem is that i havent got it connected to my PC so i cant burn anything at the moment. I'll need to look for a soundcard with optical and coaxial in and out........
Or maybe build USB in my reciever?

As far as the quality of the different stations...they vary ALOT. I'l have to check which are the best.

Coolin
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Old 30th November 2005, 04:05 PM   #10
stevers is offline stevers  France
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Default Squadra's reply

Squadra,
You seem to have answered (nearly) a question I posted after this thread.
How did you get at the SPDIF signal and what DAC did you use?
I'm using a Panasonic Sky Digibox in central France to receive mainly BBCR3. The beeb don't like it but, until they produce a satellite footprint the exact shape of the British Isles there's not much they can do. Sometimes the sound is excellent, usually in the evenings from a live broadcast. The box has a mysterious panel on the back marked 'digital interface' but no indication of what's in there.
I got this email from the beeb when I asked them about broadcast quality :-
'The reason for the drop in quality at various times of the day is due to the broadcast of Radio 5 Live Sports Extra. The BBC has limited bandwidth with which to broadcast its services and to fit Radio 5 Live Sports Extra whenever it is broadcasting - the BBC has to reduce the bandwidth available to other radio services to create enough space for its inclusion. It is not broadcast all day, only when it is broadcasting live sport. This means listeners to BBC Digital Radio services will experience a reduction in sound quality whenever 5 Live Sports Extra is broadcasting.

I appreciate you feel the signal quality should be better and the BBC is looking at improving it, with the limited bandwidth currently available.'
Any help/advice on what's under the coverplate and what DAC to use would be much appreciated.
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