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CDX reverse engineering


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#41 Dubba Dutchdj

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Posted 28 September 2016 - 03:22 PM

Obviously I have sweet eff all useful to add to this thread but I feel driven to state serious amounts of man geek love up in the place, you guys are rocking my world right now! Really looking forward to see how this all plays out.
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#42 Flexinoodle

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Posted 28 September 2016 - 11:34 PM

To be fair it is all Rasteri doing the work, Mutis hunts any info he can to help, the rest of us are on the sidelines cheering like little bitches !!
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#43 rasteri

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Posted 29 September 2016 - 01:57 AM

Thanks for the encouragement Dub/Flex.

The servo board is being pretty forthcoming :
 
NeDVLIJ.png

Took a while to work out what all the signals did (it didn't help that they're mislabelled on the fucking PCB...), and had to learn more about CDs than I ever thought I'd need to, but it's mostly sussed now. Gotta start thinking about how I'm gonna connect a microcontroller to this thing.

EDIT : oh also, mp3 mode needs to be investigated, I didn't have any more blank CDs left today though, haha.
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#44 Dubba Dutchdj

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Posted 29 September 2016 - 08:18 AM

Mislabelled PCB..... brilliant
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#45 Mutis Mayfield

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Posted 29 September 2016 - 01:11 PM

To be fair it is all Rasteri doing the work, Mutis hunts any info he can to help, the rest of us are on the sidelines cheering like little bitches !!


It's was I thinking but from non knowledge user it could seem I am rocket scientist xB
Rasteri is the Master Ninja I only try to bring some rice <3
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#46 Dubba Dutchdj

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Posted 29 September 2016 - 01:48 PM

I can change light a car light bulb at push..... your freaking ninjas speaking next level language in this thread, crazy skills 


ETSG 3 is dope, It made the watch words for last nights cuts in Rye - "Fuck attack"


#47 Mutis Mayfield

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Posted 29 September 2016 - 02:11 PM

Sometimes friends giving support is the best tool one need to continue freakin'. Almost in my own I really appreciate all the mood of the forum members and of course the great job does Rasteri as usual. The cdx mod performed by my friend Norbert was really possible thanks to Rasteri contributions at Ucapps (scratcher box) and my part was being a nightmare coach for Norbert xDDD

Also the few or much I've learnt over the years was a mix between researching and sharing in loop mode. ;)

Edited by Mutis Mayfield, 29 September 2016 - 04:04 PM.

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#48 Flexinoodle

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Posted 29 September 2016 - 03:11 PM

Rasteri, what software is that ?


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#49 rasteri

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Posted 29 September 2016 - 05:03 PM

It's the front end for a Saleae Logic 8. It's not very good but it's cheap.
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#50 Flexinoodle

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Posted 29 September 2016 - 06:34 PM

Im looking at it for days now thinking "How the flip has he got a DAW that i dont know, I am DAW master no 1" hahaha

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#51 rasteri

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Posted 02 October 2016 - 07:57 PM

Spent the weekend poring over CD specifications and component datasheets and I'm thinking maybe the mp3 board will be the one to replace after all. The servo interface turned out to be more complicated than I thought, what with its subchannel interfaces and linear-feedback shift register scramblers and even-odd byte sequencing and so on.

Replacing the mp3 board will also give us more flexibility, like FLAC support etc. I was going to try and emulate the I2S interface this weekend but the chip I was gonna use (STM32) doesn't allow 24bit frame sizes. I really wanna use the STM32 because they're really powerful, so maybe I can hack 24bit i2s by generating the LRCK using an external counter chip synced to the bitclock, or something.

EDIT : (note for future Andy) you could use two i2s peripherals, using one for the PCM out and one for the LRCK
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#52 Flexinoodle

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Posted 02 October 2016 - 08:40 PM

You lost me at spent hahaha

So if you can add formats, which are looking at besides wav/mp3/flac ? Is there anypoint to any of the others ?
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#53 Mutis Mayfield

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Posted 02 October 2016 - 11:12 PM

Little offtopic:



FPGA based, maybe useful if stm32 doesn't fit your needs and you want to explore these path. It has all the resources at "more info" in yt (it was reviewed at djtt few months ago)

End ot.

Edited by Mutis Mayfield, 02 October 2016 - 11:14 PM.

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#54 rasteri

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Posted 23 October 2016 - 06:31 PM

I managed to get some stuff done this weekend.

It seems that the only signals which need to be emulated to fool the DSP into thinking there's a CD present are the I2S signals from the MP3 board (BCK, LRCK, PCMD) and the subcode readout from the servo board (WFCK, SCOR, SBSO). The subchannel protocol confused me for ages because they weren't clocking enough bits on EXCK to read the whole subcode, but it turns out they're using a trick so they only have to read the Q-channel (which is what holds things like the CD's table of contents, etc). I wrote a program to decode the servo's output and sure enough :

xQgh5h8.png

Interestingly there's a huge number of Sub-Q packets with invalid CRC because the CD drive is really knackered in this CDX. There are nasty audible clicks in the audio too.

There's a line of STM32 chips that can do I2S output at 24-bit, so I've ordered a dev board :

v7kEodt.jpg

Hopefully I can have a proof-of-concept working soon.
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#55 Mutis Mayfield

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Posted 23 October 2016 - 11:50 PM

Amazing work Rasteri. Congrats!

#56 Flexinoodle

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Posted 24 October 2016 - 10:11 PM

Off the chain, still waiting for a big enough box to send you your second one ;)
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#57 ericuk

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Posted 26 October 2016 - 12:05 PM

this wank worthy thread may possibly go down in history as a goat or whatever cool people call it.

 

p.s I don't understand the techy stuff, just how amazing it would be to have a working cdx without the shitty cd drive.


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#58 DJ Rock Well

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Posted 26 October 2016 - 12:08 PM

this wank worthy thread may possibly go down in history as a goat or whatever cool people call it.
 
p.s I don't understand the techy stuff, just how amazing it would be to have a working cdx without the shitty cd drive.


I think you speak for a lot of us with those sentiments!
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#59 ximo roca

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Posted 26 October 2016 - 05:23 PM

very interesting thread!

 

love what your are doing, and hope ur succesfull at it.

 

I have a pair of sl-1200-dz i want to mod too. There is this platter mod diy kit as a starters and then the idea would be adding a rpi dvs inside. I unsure about that though since the screen has to be outside anyways, keeping the whole dvs sistem boxed in the screen would make it portable and interchangeable with other units.

 

best would be some bare metal programming, but im tottally clueless about that. But the technics should have some neat possibilities because of the way it tracks the relative position and the speed. Its a clear film attatched to the platter and a photosensor reading through it which determines the direction and speed of the playback, this means its basically relativemode timecode, if you can manage to see what sort of algorithm its using. Heck you could probably just connect those 3-4 pins into rpis gpio directly to be used as the "timecode".

 

If that was possible you could actually empty most of the cd inside and run the unit through software, or it could even make a reasonably easy way to mod any turntable with just that film a sensor and pi.


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#60 Flexinoodle

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Posted 26 October 2016 - 05:50 PM

Modding relatively expensive gear like the Technics is a fools economy, these CDX are pennies on the pound for now because of a shitty $2 cable inside, and the fact that CD is about as popular as herpes.

I would not mod that Technics if you paid me to do so, in ten years when the modded one is worth $10 and an original is worth $1000, you will be kicking yourself.

Some stuff is collectable, some stuff is Rasteri-able hahahahaha


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