Dolby Digital/DTS to SP/DIF

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
There is one thing that I've never seen mentioned, and that is:
Is there any product on the market that can take in an encoded Sp/DIF bitstream, and decode it to three seapate sp/dif bitstreams i.e.

AC3/DTS/PCM -> decoder -> PCM Front L+R, PCM Real L+R, PCM Sub + Centre

which can then be fed to the audiophile DACs of choice.

Alternatively, do the commercial decoders employ generic DACs that can be tapped for the digital signals (maybe in I2S format, if not SPDIF)?

As another alternative, those of us with HTPCs should be able to do this in software, but it seems that there are no sound cards that have :att'n:discrete:att'n: (i.e. decoded) digital outputs instead of the cheesy 5.1 analogue outputs that come as standard.

This should be a fairly straighforward DSP project, apart from the DTS decode function, I would have thought, and would be ideal for a quality 2-channel setup that is to be expanded to a full home cinema.

Cheers,

Arnie
 
I think they are all covered under non-disclosure agreements, and you also have to license the software to make them do anything useful. But, you could conceivably pull the chip (a PLCC) and its EEPROM out of some existing equipment.

I'd propose to simply hack the right hardware and software into a home theater computer.
 
Cost

Hacking the hardware from an existing decoder looks like the only realistic option of obtaining these chips, unless anyone knows of a renegade Dolby licencee...

There is one small flaw - one of the main reasons for (me) doing this is to use my brain to save some money, that's not going to happen if the only source of components is a finished product.

The other option - using a PC to do the decoding, would just need a sound card that has three digital outputs, but it looks like all the cheap cards use the CMI8783(?) chip, which has just SP/DIF passthrough or analogue. And as far as I can tell, no software decoders have any way of sending each pair of channels to a different sound card (3 sound cards = 3 sp/dif outputs).
 
Already the "old" Soundblaster Live soundcard included 4 digital outputs (exists at least on my SBLive Platinum), and the newer 5.1 version has 6 outputs. They are located on a separate bracket that is connected to the pins on the board. If I remember right it is a mini-DIN connector. It is supposed to be connected to an external digital speaker system.
 
johan said:
Already the "old" Soundblaster Live soundcard included 4 digital outputs (exists at least on my SBLive Platinum), and the newer 5.1 version has 6 outputs. They are located on a separate bracket that is connected to the pins on the board. If I remember right it is a mini-DIN connector. It is supposed to be connected to an external digital speaker system.

Yep. Should work fine I imagine. I2S also available at the header i believe.
 
Please excuse my ignorance, but are you sure that these outputs are for all 6 of the output channels, rather than being e.g. one input sp/dif, one input toslink, one output sp/dif, one outpu tosling and one for a cdrom?

If so, that would be ideal! Except that I believe Soundblasters re-sample everyting to 48kHz internally...

I may have to have a look at the Creative site to check.

thanks.
 
I do believe (from memory) that these are independent signals. I don't know how it works on the newer models, i.e. how do they encode six channels from normal stereo sound. My version at least is able to generate surround sound to the two rear channels.

And yes, all SBLive encode the sound internally to 48 kHz. It is stupid. If you record an external digital sound with 44 kHz, it internally re-encodes it to 48 then down to 44 again. And output is always 48 kHz. I heard some rumors that Audigy and Audigy 2 can output other sample rates, but I suspect that they internally use 48 kHz anyaway. This is ****, I am going to change to Terratec cards. They have true 24/96 support.
 
Time for a new thread...

So, as I suspected, Soundblaster is still not an option.

It would be really nice to make the PC a home entertainment hub - there's enough processing power for sure, it's a case of getting suitable hardware peripherals.

My ultimate plan is to have the PC act as a control centre (using girder) and a/v digital decoder, outputting to dacs where appropriate.

For instance, it could be the controller for a complex source switcher of RGB, S-Video and audio components, but all analogue signals would be handled by an external relay box (connected by fibre so no PC noise would get into the analogue ground). Add an LCD module and some front panel buttons, and I would have a very powerful hub.

A digital tuner card would turn it into a lossless HD recorder (bye-bye VHS).

A sound card with 3 sets of sp-dif outputs would take care of audio decoding (bye-bye pro-logic decoder, hello stacked DACs).

And all controllable from the office. No more relying on the wife to set the video...

Apart from the sound card, I think I can put everything together.

As for software, one problem that I haven't sussed so far is how to use the PC as a pro-logic decoder IN REAL TIME from a line-in i.e. for terrestrial TV.

Any ideas?
 
I am also going for a similar thing, but I have excluded the LCD. One option is to buy a Shuttle XPC. These small and very quiet PCs have everything integrated: 100 Mbit LAN, Sound S/PDIF in/out, VGA, Video out (newest model has Composite, S-video and RGB!), and has expansion slots, 1 AGP and 1 PCI for adding a better sound card and video card, maybe if you want to record also. There are also Firewire and USB 2.0 ports. The ultimate solution would be to run Linux on it. Then I could control it from anywhere. S/PDIF out (optical Toslink) is enough to run my digital receiver and no bulky computer monitor is needed. Maybe a wireless keyboard and mouse to control it locally.
 
Perhaps this should go somewhere else

I've gone for a rather different option:
1. Desktop ATX case. It's saame width as normal hi-fi components, so will slot in above vcr etc. under TV.
2. Asus A7V333A, Athlon XP1600+, 256Mb RAM. Processor was unbelievably cheap for what it gives, and components are nice generic shape i.e. easy to upgrade, when the time comes.

3. Generic Geforce 2 MX400 TV card. Cheap, passive cooling, not bothered about games, but enough power to run most games @ 50fps. Using powerstrip to UNDERclock it to reduce heat even further, and TVTool to control overscan. ATI cards cannot overscan properly on PAL system, so I've heard. Not enough info about SiS to make a choice there.

4. Audio supplied by onboard audio. Analogue outputs are suprisingly clear, so leaves time to do other tasks before attacking this one (hence this thread!).

5. BTC 5090 wireless keyboard. Has built in mouse-type device (an 8 way pressure pad) which is OK. keyboard is v. smart, has good range and was cheap.

Planned options:
1. VFD/LCD display + front panel keys for play, pause etc.
2. Girder to perform all necessary program manipulation.
3. UIRT2 will allow PC to control TV, VCR, Cable decoder, pre-amps etc. Also has GPIO so can use it to e.g. trigger widescreen mode on SCART connection to TV and change inputs/volume on pre-amp.
4. Find sound card with sp/dif output for each channel, link to outboard DACs.
5. Modify front speakers (Mission 752Freedom) with active crossovers and amplification. I've just read about what's going on with class D amps in the forums here - wouldn't it be great to use the PC as a DSP, feeding the woofer and tweeter amps directly with a digital signal. The room for tweaking and optimisation would be vast!
6. Paint the PC a nice colour, and swap the green/yellow LEDs for blue and white.

Well, that should keep me occupied for a while. :D
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.