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Old 11-10-2003, 12:53 AM   #61
TulaneJeff
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Upgradeable firmware (channel map changes, etc) is quite different from native audio decoding support. I doubt the latter is able to be changed by satellite. The majority of the functions are built into the receiver at the factory.

They can tweak and upgrade encoding methods at the transmission end all they want, but at the end of the day the tuner is inherantly frozen (chipset feature set) in how it can decode the signal.

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Old 11-10-2003, 01:02 AM   #62
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no offense guys but were getting as bad as the xm fan site.no im not dogging xm at all but almost every time i post on there the moderator takes it off when im not dogging xm at all.i have listened to xm recently and i do beleive sirius is sounding better as of right now but who knows xm may have something big happening and there not going to release it until they know its perfect.dont get me wrong here but i do think sirius likes to throw stuff out without testing it too much which is great but it will make the sq vary quite a bit as they mess around with the algorithms.there both great services and its still new technology thats why neither of them are exact cd quality yet. one day it will happen but as of right now im happy with sirius.
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Old 11-10-2003, 01:02 AM   #63
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This is an interesting link. It only reinforces my thoughts that PAC or AAC is native in the chipset and not a flashable feature. I'm sure there is a flash trigger to enable said feature, but that is not what we are arguing.

http://members.fortunecity.com/ezhong/resume.html

Quote:
Firmware Engineer (03/02 - present) Agere Systems, Inc., Holmdel, NJ

Worked on wireless communication chipsets and systems development.

Worked on a video-over-WiFi project. The project is to deliver MPEG2/MPEG4 video over 802.11 WLAN. Did prototyping work on the Altera Excalibur FPGA platform. Software development was based on an ARM922Tâ„¢ processor integrated in Excalibur.

As a core member in digital backend firmware development, continued working on a satellite radio project called SDARS. Work focused on the 2nd generation chipset development for Sirius Radio receivers. Responsibilities included:

-Firmware migration onto a new all-in-one baseband chip.

-Adding AAC+ audio codec to the 2nd generation SDARS chipset.

-Working out receiver value-adding features together with customers.
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Old 11-10-2003, 01:06 AM   #64
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Quote:
Originally Posted by kenny6699
no offense guys but were getting as bad as the xm fan site.
That's a bit of a stretch.

The difference is we are not XM or Sirius bashing, we're having an intelligent academic debate. The merits of each audio codec is a hot topic and we're trying to get to the bottom of it.

You are right in the fact that the average listener should care less about what we are discussing.

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Old 11-10-2003, 01:17 AM   #65
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Wow Tulane, that is an interesting post!

Did you read the line that says this guy added AAC+ to the 2nd Gen receivers!? Wow, that's a doozy.

If you read that, it sounds like Sirius has AAC+ planned for their service! I wonder if that would be the "codec upgrade" you speak of?
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Old 11-10-2003, 01:20 AM   #66
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Okay, can we call a truce.

1) The audio processing codec is native in the chip (enabled by flash?)
2) Sirius may or may not use AAC in the future. But it looks like they will.

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Old 11-10-2003, 01:30 AM   #67
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OK, I am believing more that the codec is IN THE CHIP, but am still not completely convinced... it just sounds terrible. Like if they switched to AAC+ wouldn't that mean everyone with a 1st Gen receiver would have to upgrade?

But other than that, truce man, though I didn't have much argument with you to begin with. But again, THANKS FOR THE INFO.
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Old 11-10-2003, 01:33 AM   #68
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I'm not completely certain, so let's keep digging. It does look like the most logical analysis from what I've seen. This has been enlightening for me and you both.

It wouldn't surprise me at all though if XM hid the fact that their chip had native PAC and AAC support from the beginning in an effort to one-up Sirius.

Good to see Sirius future proofing their Gen2 equipment though.

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Old 11-10-2003, 01:36 AM   #69
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I bet you this Eric guy whose resume that is would definetly be able to settle this once and for all...

This completely turns upside my idea of the way sat radio worked, though.

Either way, I consider it good news that Sirius has AAC+ planned, or at the very least has it strongly considered. But if there is a new PAC I don't know about that is about to be released that blows away AAC+, I'm all for it. So *when* is this codec upgrade going to happen?
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Old 11-10-2003, 01:39 AM   #70
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Quote:
Originally Posted by ctwickman
Like if they switched to AAC+ wouldn't that mean everyone with a 1st Gen receiver would have to upgrade?
Well that would assume that they will in fact switch to AAC+.

But wouldn't it be clever if they devised a way to support legacy receivers by transmitting an optimized signal that offered better sound, yet still decodable by Gen1 tuners, as well as an advanced audio codec that the new receivers could leverage.

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Old 11-10-2003, 01:42 AM   #71
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Quote:
Originally Posted by ctwickman
So *when* is this codec upgrade going to happen?
I really have no idea. Rest assured I will confirm when it happens.

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Old 11-10-2003, 01:47 AM   #72
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Quote:
Originally Posted by TulaneJeff
But wouldn't it be clever if they devised a way to support legacy receivers by transmitting an optimized signal that offered better sound, yet still decodable by Gen1 tuners, as well as an advanced audio codec that the new receivers could leverage.
That is definetly a possibility. Sounds pretty fantastic though.
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Old 11-10-2003, 02:04 AM   #73
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I find it interesting that AAC is really a PAC derivative algorithm (gleaned from reading the links in this thread). I'm not up on exactly how the decoder altorithms work, but from what I've heard, they are much more simple than the encoder part. It may be possilbe to make great strides in the encoder part without the need to change the decode part, especially if you assume that XM switched without upgrading the flash on their radio.

Another thing that we know from both XM and Sirius is that they expect to get as many as 20 more streams out of the existing bandwidth over time as technology increases. I don't know how they could expect this to happen without upgradeability in the CODEC's because once they have a few million installed radios, I just don't see how they could obsolete them in favor of a new algorithm.
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Old 11-10-2003, 02:40 AM   #74
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I'll just point this out, but you guys did most of the legwork and guessing.

In the gentleman's resume above, it mentions "Adding AAC+ audio codec to the 2nd generation SDARS chipset.". This could be the answer to the question you have been asking.

AAC+ is just another name for AAC with SBR.

Spectral Band Replication, or SBR, is basicially a way of increasing the quality of low bitrate AAC files/streams. I believe SBR does not work above 96kbps.

To utilize the extra information provided by SBR, the decoder needs to be aware of it and know how to handle it. The trick, as you guessed, is that files/streams encoded with the additional SBR information are backwards compatible with AAC decoders without SBR. If the decoder is SBR aware, it will use the information to generate better output. If the decoder is not SBR aware, it will decode it like a plain AAC file and discard the SBR information.

So, in theory, the whole thing could look something like this as far as Sirius goes.

1) 1st generation hardware is capable of decoding ACC.
2) 2nd generation hardware is capable of decoding AAC+.
3) Sirius will migrate to an ACC+ stream, allowing the second generation units to have better quality while the first generation units remain unchanged.

If you want to learn more about AAC, I would reccommend these two sites.

Hydrogenaudio's AAC Forum
AudioCoding's AAC section

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Old 11-10-2003, 02:47 AM   #75
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Quote:
Originally Posted by Manco
It may be possilbe to make great strides in the encoder part without the need to change the decode part, especially if you assume that XM switched without upgrading the flash on their radio.
This is very true. For the most part, the encoder is the key. SBR is kind of a unique situation where the decoder changed after the fact. Usually, as is the case with mp3, the decoder never changes. mp3 quality has gotten much, much better over the years - but the decoders remain virtually the same. The magic is in tuning the encoder to churn out better results. This is done over many hours, days, months, and years.

Quote:
Originally Posted by Manco
Another thing that we know from both XM and Sirius is that they expect to get as many as 20 more streams out of the existing bandwidth over time as technology increases. I don't know how they could expect this to happen without upgradeability in the CODEC's because once they have a few million installed radios, I just don't see how they could obsolete them in favor of a new algorithm.
The idea they are operating under is that the codec will get tuned to handle low bitrates better. They are figuring that over time the encoder will be able to churn out the current quality at a lower bitrate, allowing them to open up more room for more channels.

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