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Old 1st December 2003, 01:13 AM   #1
Benjlv is offline Benjlv  United States
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Default AC3 over USB

I have been looking for quite some time and have not been able to find a set of chips that will let me send AC3 over the USB connection.

My experience is only in that of the hardware area so I would like to find something that will setup similair like the the PCM2900 and PCM2700's inferace... you know automatically...

even better would be over firewire.

thanks guys/gals
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Old 1st December 2003, 06:38 PM   #2
Benjlv is offline Benjlv  United States
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should also specify that im trying to do this from a DVD playing program such as WinDVD or the like.
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Old 2nd December 2003, 11:01 AM   #3
sangram is offline sangram  India
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Umm, maybe I'm out of my depth, but you mean something lke the USB soundcards such as the Extigy and the M-Audio Sonica?

My guess is that there are custom drivers for those sound devices so that the AC3 can actually travel over the USB connection and be decoded in hardware. So that would make it software driven, with the actual decoding hardware being in the external card, and the software just telling the bitstream where to go. I don't have access so can't confirm, but suspect the drivers have no clue as to the content of the signal, only that the destination is the soundcard and the decoding will be in the card itself. This will also depend on the power of the card's DSP...

I do not know of hardware that will allow the entire AC3 stream to be re-encoded into a single stream from the 6-ch output of say WinDVD, and push it out through a digital pipe - with the exception of the Soundstorm from nVidia, but that is not USB, but S/Pdif. and besides it is very proprietary. But it will not help as WinDVD is anyway capable of putting the digital AC3 for traveling through the digital out of a soundcard, to be externally decoded.

Would this be for a multiroom HTPC configuration, by any chance?
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Old 2nd December 2003, 06:40 PM   #4
Benjlv is offline Benjlv  United States
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no it isnt...but could easily be implemented to do so...

The latest version of WinDVD has a option to send digital out on SPDIF to a "External Digital Decoder"...so winDVD does have the support. What i dont have is hardware to get the signal out of my computer. I have a Dell Inspiron Laptop in a college dorm setting that i use for my DVD playback through the computers video out.

The computer uses sigmatel's 9750 AC97 chip for the sound...(http://www.sigmatel.com/audio/stac9750pb.htm) which has very very poor output. So im looking to build a USB setup with a DAC to improve the sound. Its still a very pliminary design, but I would like to somehow extract AC3 from it to use in my dolby digital reciever and be able to fully utilize my surround sound setup.

anyways the sigmatel chip has a pass through built into it the pass any signal sent to it out a SPDIF output. But Dell decided not to impliment it on this model laptop Im tempted to open the thing up and enable it though...but the risk is to the tune of $1400 if something goes wrong while im inside.

So basically what im trying to do is get AC3 out of this thing in SPDIF format....preferably across USB and then have that go out to my reciever. At least thats Phase 1 of this ordeal.

Phase 2 will take PCM audio formats and decode them very nicely with DAC and then send that to a nice sweat headphone amp.

perhaps i will download some of creatives and m-audios drivers and see what they're all about. (wish i knew more about software)


oh one of the chips i am looking at doing this with is texas instruments TAS1020 as it will interface with a AC97 codec chip...but im not sure aas of yet if this interface will allow AC3 to be passed through the USB then to the AC97 chip and out like the sigmatel allows. I will be looking into this tonight....
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Old 2nd December 2003, 07:15 PM   #5
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Not sure which inspiron you have, but my 5000e had digital out only on the port replicator. you might be able to find a refurb one from Dell.

My current 8200 has it built into the video adapter - the connection looks like an s video connector with a couple extra pins. you can connect S-video directly to it, but need the dongle to get digital out. Maybe yours has a stealth digital out, too.
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Old 2nd December 2003, 08:00 PM   #6
Benjlv is offline Benjlv  United States
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yeah ive got the dongle....thought it would work since it did on the 8500's but turns out that they didnt on the 5100's that are out now.

I looked it up in their service literature....the 8500's lists the pins as having a SPDIF out...but the 5100 has nothing on those pins
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