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Old 20th June 2005, 09:24 AM   #1
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Lightbulb 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?
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Old 21st June 2005, 01:01 PM   #2
macboy is offline macboy  Canada
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Default Re: The Quest for the holy DIY Decoder

Quote:
Originally posted by theodoric
...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.
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Old 21st June 2005, 06:30 PM   #3
gmarsh is offline gmarsh  Canada
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Default Re: Re: The Quest for the holy DIY Decoder

Quote:
Originally posted by macboy
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.
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Old 24th June 2005, 11:05 AM   #4
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Quote:
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...
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Old 28th June 2005, 06:21 AM   #5
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Lightbulb 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...
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Old 30th June 2005, 08:23 AM   #6
arasuk is offline arasuk  India
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Default creative DDTS -100!!!!

Hi Benstrom,

Quote:
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
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Old 30th June 2005, 03:22 PM   #7
gmarsh is offline gmarsh  Canada
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Default Re: The first sniff of success...

Quote:
Originally posted by theodoric
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.
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Old 2nd July 2005, 09:41 AM   #8
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Hi Arasuk,
Quote:
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


[IMG]http://[/IMG]
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Old 11th July 2005, 03:57 PM   #9
mik is offline mik
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I also have DDTS-100 but I did't use it because i must finish my speaker first, I was not aware of downmixing problem until I find this tread so can you tell me if I can do this way?
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Old 16th July 2005, 11:21 AM   #10
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Quote:
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...
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