The Quest for the holy DIY Decoder

Hi All

I know! I know! It has been discussed a lot, many have tried, scuffled about looking for chips and info, but none succeeded.

Nevertheless, I decided it might still be worth looking for a chink in the armour of the Dolby & DTS chips manufacturers in my quest to create my fully digital home theatre system.

This morning I have sent a request to Cirrus for their decoder and post-processing chips. Strangely enough, their website allows you to select these IC's on the sample request page. I will drive this request as far as I can humanly go in order to obtain these chips.

In the meantime I will be starting on schematics and board layouts and also keep going on my various other projects.

I will keep anyone interested updated. Who will join me?
 
theodoric said:
...This morning I have sent a request to Cirrus for their decoder and post-processing chips. Strangely enough, their website allows you to select these IC's on the sample request page....


As mentioned in the forum countless times, almost all of these chips require firmware to do their magic. They simply will not decode DD or DTS without this code installed. Getting your hands on that code requires proof that you have a Dolby or DTS license. There are a couple exceptions (chips pre-programmed to do DD) but those have proven exceptionally difficult hard to get your hands on, with minimum orders in the thousands.
 
Re: Re: The Quest for the holy DIY Decoder

macboy said:
As mentioned in the forum countless times, almost all of these chips require firmware to do their magic. They simply will not decode DD or DTS without this code installed. Getting your hands on that code requires proof that you have a Dolby or DTS license. There are a couple exceptions (chips pre-programmed to do DD) but those have proven exceptionally difficult hard to get your hands on, with minimum orders in the thousands.

Fortunately A/52 (Dolby AC3/Dolby Digital) is a published standard - it's part of ATSC HDTV. There's open source code out there (eg liba52) which can decode it. Potentially, someone could pick an off-the-shelf floating point DSP chip, code an A52 decoder for it and make their own DD decoder... someone other than myself (i've already got one DSP project that I have zero free time to work on)

You don't need a license to decode DD, but you need to be licensed in order to sell a product that decodes DD.
 
Fortunately A/52 (Dolby AC3/Dolby Digital) is a published standard - it's part of ATSC HDTV. There's open source code out there (eg liba52) which can decode it. Potentially, someone could pick an off-the-shelf floating point DSP chip, code an A52 decoder for it and make their own DD decoder... someone other than myself (i've already got one DSP project that I have zero free time to work on)

well, I did it some 5 years ago. Code is running on DSP56303evm card using an external multichannel codec. It's a 24bit fixedpoint dsp. Excellent sound though the codec could be better (CS4226).
It took hell lot of time to do it but I wanted to learn mixed c and assembly coding for motorola dsp.

If someone really wants to build a good cheap DIY DD-preamplifier, go and buy Creative DDTS-100. You will get DD,DTS, prologicII, DD ex, etc...Inside you have motorola DSP56367 and decent burrbrown 24bit DA-converters.
Place the electronics in a better case, redesign the analog opamp part, replace all digital attenuators after DA conversion with better quality attenuators. You could even place a second DSP after the original to perform fancy lfe equalizing and other filterings to match your audio system and what original DDTS-100 lacks, delays...
 
The first sniff of success...

After a few days away from the office, I opened my email this morning to find a very nice one from Cirrus. It's the standard "What is your project and what volume do you expect?" that you usually get from these companies. However, there was no indication of licenses or other obstacles.

I know this can still fail at a million stops along the way, but I am getting the sweet smell of success. Just a hint of it, but still.

Just for interest sake, the parts I ordered were:

CS49326 - AV Receiver:
Dolby Digital, Pro Logic, Pro Logic II, Virtual Dolby Digital, MPEG-2, MPEG Multichannel, MP3, DTS Digital Surround, DTS-ES (Discrete & Matrix), DTS Neo:6, LOGIC5, LOGIC7, VMAx, SRS TruSurround, SRS CircleSurround I/II, HDCD, Cirrus Extra Surround, Cirrus PDF (PCM upsampler & Pro Logic 2x Fs), Cirrus PL2_2FS (almost same as PDF)

CS49330 - Multichannel post-processor:
THX Cinema, THX Surround EX, Cirrus Digital, multichannel effects

If I actually receive these, I should be able to build one SWEET processor, huh?

Let's see what happens...
 
creative DDTS -100!!!!

Hi Benstrom,

If someone really wants to build a good cheap DIY DD-preamplifier, go and buy Creative DDTS-100. You will get DD,DTS, prologicII, DD ex, etc...Inside you have motorola DSP56367 and decent burrbrown 24bit DA-converters.


Can you provide more information on this product as I am looking for a decoder too!!

Can this be hooked for the regular dvd players

Thanks

Arasuk:D
 
Re: The first sniff of success...

theodoric said:
If I actually receive these, I should be able to build one SWEET processor, huh?

Let's see what happens...

Looks like you might get chips you won't be able to do anything with..

http://www.cirrus.com/en/pubs/appNote/an162-2.pdf

page seven, lower left... looks like you'll need to present Cirrus with proof of Dolby/DTS licensing before they'll give you the code you need to run on the DSP.
 
Hi Arasuk,
Can this be hooked for the regular dvd players
Yes it can. DDTS-100 has 3 digital, 1 coaxial and 3 analog inputs. It can be configured to output 7.1 or 5.1.
If you want to hook it up to a home theater system, two things must at least be done:
- replace all outgoing jacks with RCA-connectors
- if you are using subwoofer: DDTS has lfe channel out. But there´s no downmix from other channels into lfe. I think it is done in creatives separate speaker set. I have done a modification to the existing inverting lfe-opamp. It is now a summing opamp which sums all 6 channels and after it there's a separate opamp performing 4th degree lowpass filtering, matched to my subwoofers.
Look at the pictures.

For me, this is only a temporary solution. I'm planning to move the digital board in a better case, redesign analog part to use double sided power supply and replace attenuators and also redo the interface.
And if separate delays to each channels are needed: to put in an external dsp


[IMGHTTPDEAD]http://[/IMGHTTPDEAD]
 

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I was not aware of downmixing problem until I find this tread so can you tell me if I can do this way?

Yes. I don,t use those separate 24dB active crossover filters, cos my speakers are small. For summing and lowpass part I use creatives own single supply.
Maybe DDTS-100's DSP56367 has downmixing features inbuilt in rom but creative does not take them in use.
Would be nice to now...
 
Hi Benstrom,

do you have a schematic of the DTS-100, I would like to put the electronic into a new case as suggested and I want to combine the device with a post processing dsp and new DACs or SPDIF outputs.
the audio quality of the DTS-100 is not as good as I hoped. I don't like the clicks and plopps during muting and source switching!

btw, does anyone have the standards or any code for DD and PL2... ?
Perhaps it's better to code my own decoder on a TI 6713 DSK as it's more powerfull even for postprocessing?!
 
btw, does anyone have the standards or any code for DD and PL2... ?
Perhaps it's better to code my own decoder on a TI 6713 DSK as it's more powerfull even for postprocessing?!
If you did create a DIY DD decoder, you would be the DIY audio god. Many people have flirted with the idea here and nobody has had the guts (or brains?) to do it. It shouldn't be too difficult as there are open-source DD decoders (PC-based) out there to start from.

Here are some references to get you started, beginning with the AC-3 specs:
http://www.atsc.org/standards/a_52a.pdf (140 pages of technical goodness).
Don't forget the errata: http://www.dolby.com/tech/ATSC_err.pdf
http://liba52.sourceforge.net/
http://ac3filter.sourceforge.net/
DTS:
Spec from ESTI: http://webapp.etsi.org/action\PU/20021224/ts_102114v010201p.pdf
An open sourced library "libdts" was created, and re-named to libdca after DTS sent their lawyers after the developers. As a result of that, the sources are hard to come by, but you should be able to find them on Debian, here
 
I have seen an implementaion on a TI 6713 DSP but did not get the code for it as it is IP. The presented code consumes about 20% of the computational power of a 225 MHz version. Seems to be much space for furter filtering like equalisation...
Yesterday I looked at the standards as suggested - much to read!
Have to find out more.

Cu
 
Hi,

Just thought I'd give a quick post about the Creative DDTS-100 decoder.... I've been looking for a decent decoder for future integration into a DIY surround processor / amp project, and the Creative decoder looks like a great option. It's even got the same Motorola DSP IC which is used in many AV receivers these days and has quite a large following for software support.

I was wondering if anyone here thought it might be possible to re-program the DSP chip on this decoder for adding EQ and delays etc., or would the chip likely be far too busy decoding the Dolby or DTS streams in the first place?

I would be VERY interested to see how simple the control messages are between the MCU and DSP in this decoder for switching between the different decoding modes. It looks like the MCU is an NEC UPD789026 8-bit CPU with 16KB of Flash memory. Here's a Korean page with a few more internal photos of the decoder......

(Many thanks to benstrom for posting the original photos btw!)

http://www.kbench.com/hardware/?cc=9&sc=0&no=22959

You can translate the page with Altavista if you like, but it won't make much sense. Some of the translations are great for comedy value though.... "The reason which is accurate actualness it does not know well anyhow but it confirmed the DSP and is closed with the hazard iron which it sees to carry out the region which it tried."

Hazard iron! :hot: LOL!

You can download the User Manual and the instruction set manual for the NEC MCU from the following links......

http://www.necel.com/nesdis/image/U11919EJ5V0UD00.pdf

http://www.necel.com/nesdis/image/U11047EJ3V0UMJ1.pdf

There's a large amount of info. on the Motorola (now Freescale) chip online, and I'm sure some of you know 99% more about DSP programming than I do! :xeye:

http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=DSP56367&nodeId=0127958596

The DDTS-100 decoders have recently sold for around £70 on eBay here in the UK, which is a bit steep for me atm, but hopefully the prices will drop by the time I actually start to build anything. Then again, this is still a hell of a lot cheaper than buying a DSP dev kit and the Dolby / DTS licenses.

I'm hoping to eventually build a DIY 7.1 surround preamp and power amps, and also add speaker delays, and some sort of Re-EQ (aka THX) or possibly DRC (room correction) to the decoder.

This is whenever I can scrape enough money together of course. :xeye: In the mean time, you guys will probably build some more amazing stuff, so I'll definitely be keeping an eye on things!

OzOnE.