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Old 2nd June 2002, 05:06 AM   #21
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Decoder is all about obtaining the sorround channel. This is where Dolby alone holds a monopoly.

So rather than jumping into making a complete decoder, I think we should put our heads down and try to come up with a solution to get the surround channel i.e L-R and remove the dialogue leakage.

Decoding the other channels is easy. Remove the dialogue leakage and you join the biggies with your own product.

bimbla.
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Old 12th June 2002, 09:54 AM   #22
hifiZen is offline hifiZen  Canada
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Default Not gonna happen... BUT...

The only way to do this properly (especially for the critical listener) is to have the actual algorithms and do the decoding according to spec. As far as details regarding the DTS algorithms go, they are very tightly controlled intellectual properly. I work as a hardware engineer on DVD players which use DTS, HDCD and so on, and I don't have access to any of this information. Only the core technology guys who build the silicon hardware and write the microcode that does this stuff have access to the nitty-gritty details of how it's all done. Of course, even if I did have access to the details, I'd be under NDA and hence unable to disclose it to the DIY community anyway.

Such a shame, since I think it would be a tremendously interesting project to actually implement a DTS decoder or something similar in an FPGA or DSP. Exploring the educational option is probably the only viable option... I did manage to get Protel to donate a full copy of Protel 98 when I was still at university, so it goes to show that big companies can be relatively charitable if you're persistent and persuasive.

All is not lost for DTS decode, though. While you may not be able to build a DTS decoder itself, keep your eyes peeled for affordable new DVD players to hit the market in about two months which include full DTS decoding (hint, hint ). If you find the right model, you'll also get some other nice audio features like HDCD and DVD-Audio playback... Given the cutthroat DVD player market, manufacturers are under great pressure to produce feature-packed units at a very low cost. You might be able to find what you want for under $300 in another month or two... I mention this, because there's a particular model (not yet released), which I did some hardware work on, and when it comes out I'll be lining up to buy one strictly for audio use (yep, you can bet I'll be modifying it too ). If I happen to play the odd movie on it, well that's just icing on the cake!

Always remember kids... where there's a DAC, there's uncompressed, full resolution audio data...

Cheers!
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Old 12th June 2002, 02:15 PM   #23
tiroth is offline tiroth  United States
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hifiZen: I hope you'll clue us in when the time comes. ;)
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Old 12th June 2002, 05:56 PM   #24
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Default 5.1 DIY Decoder

Dont get me wrong, buying is different and making something yourself is different.
If decoding in digital domain is difficult, WE can do it in analog.
Once the algorithm in analog is understood, WE can switchover to digital.
I need support from you people to convert my design idea in analog, to a DSP algorithm.

Do I have any hands up........?



bimbla.
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Old 12th June 2002, 06:17 PM   #25
Won is offline Won
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Bimbla --

How do you plan on decoding a digital AC-3 bitstream in the analog domain? It doesn't make any sense to me.

-Won
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Old 12th June 2002, 06:24 PM   #26
tiroth is offline tiroth  United States
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bimbla, I don't see how analog matrix decoding, dialog leakage removal, etc, are remotely related to the decoding of a packetized discrete audio stream. Sure, you can create an analog matrix surround decoder, and you can port it to a digital system which operates on PCM data. There are some benefits to doing this digitally, but also some pitfalls.

Though this is digital, it is totally different than discrete decoding, and will not come close to approaching the quality of a discrete decoder...nor will it be useful in the design of such.

As others have noted, a somewhat complete GNU decoder implementation already exists. There are two opportunities for development here

1) Fix/improve the linux decoder
2) Port the decoder to DSP

I actually have a TI C6000 eval board for which decoder code exists, but TI will not supply the code without a license.
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Old 12th June 2002, 06:36 PM   #27
Variac is offline Variac  United States
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Default Oh no, thinking again

Your comment about the Soundblaster made me think that a good way to go on a decoder and/ or D/A A/D would be a DIY box with a power supply that mimics the power supply of a computer, but linear using transformers, caps etc. 5 and 12 volts?
Then you could use some of the pretty good pro cards available for A/D D/A

Also you could upgrade something like the Soundblaster as someone suggested. If you fry it they are cheap enough to buy another.Replacing componants might make a surprising difference
and people could report back their findings.

Then a Usb port for the computer to control it. I know there are outboard units already, but with this you could choose whats best for you and probably save money.
Also- the Soundblaster Platinum has a hand remote control which might do enough that we don't need computer control. I know this wouldn't be ultra fi but the component upgrade is worth a try I'd think.

I guess the trick is the Usb interface to control a card meant t o be in a computer.

Easier I guess would be a separate linear power supply, a separate box for the card and i/o connections, and a wide ribbon cable to bring out a pci slot from the computer environment. Actually that sounds pretty cool!! BUT is there a way to filter out and bad juju that originates in the box and travels through the pci cable (digital hash of some sort?) The cable could be shielded of course.
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Old 12th June 2002, 08:01 PM   #28
tiroth is offline tiroth  United States
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It would be extremely difficult to control a PCI soundcard w/o a computer. A better bet would be a micro motherboard with an available PCI slot...then just write the code for linux.

Bringing the PCI slot out of the motherboard would also be a treat...there are very rigid specs for the tranmission distances to maintain signal integrity.

If you want to toy with this, just buy an Extigy. It is relatively inexpensive and really is rather decent. However, I must warn you that I am unsure whether or not it is possible to tap the digital signals...I believe the soundblaster cards do not have DACs in the normal sense, which means there may not be a PCM stream to tap anywhere.

I do have an Extigy (some limited info here, althought the most interesting bit [DAC] is still awaiting good testing) and would be willing to do some quick testing for digital PCM signals if someone has some technical data on the Creative ICs.
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Old 13th June 2002, 11:18 AM   #29
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Default DIY 5.1 Decoder

I was trying to say too many things at a time.

This is what I mean:
Surround sound decoder is unavailable in DIY form. Let us see how we can develop one.

Options: a) Analog Decoder b) Digital Decoder ('De-packetiser')

Option b gives best results since there is no encoding and decoding of channels during recording. Each channel has its own identity (is discrete). The problem is breaking into the closely guarded technology.

Option a might sound uninteresting, but is universal since all equipment will have analog Lt and Rt out channels. We all know how Surround channel (S) is encoded. So here is our best chance to decode it from Lt and Rt signals.

Lt-Rt gives S but tow more processes in the form of expansion and delay need to be carried out.Delay should be relatively easy. So it all boils down to suppression of leakage dialogue and simultaneously increasing the gain of the effects only.
These two processes can be done in analog domain or in digital domain.

So even when I say digital domain, I am still with Pro-Logic II and not Dolby Digital or DTS. Also, the output of such a decoder will have a max of 4.1 and not 5.1 channels.

bimbla.
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Old 17th June 2002, 09:49 AM   #30
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Default 5.1 DIY Decoder

Users following this link should also check out the VT1616 audio codec from VIA Technologies, the mother board chipset maker.

If anyone has an application note for the same, kindly PM me.

bimbla.
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