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X5 total audiophile remode. BIG Question for the programmers- authors of builds.

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Alex_Nsk:
Hi everybody! I'm new member of rockbox forum from Siberia, Russia!
I'm happy owner of rockboxed + flashmoded Cowon X5.
Some pictures 'bout modifications can be seen here: http://www.player.ru/talk/showthread.php?t=59891
And now I working to reach the best possible sound with this item..
Right now I can connect X5 throu I2S@16bit bus to the my home audiophile multibit  DAC, it sounds great, but I want more audiophile sound on a walk mode...
I plannin to made a little board whith brand new audiophile DAC & powerfull headphone amp, and put it inside the X5L instead of it's second little battery.
To reach the best possible sound I'm plan to use TI PCM1798 + AD8620 buffers + TPA6120 headphones driver.  PCM1798 can work with up to 24bit*192kHz input PCM.

So my question is: is it possible to cansel limit on 16bit PCM words output from the Coldfire CF5250? There are 32-bit floatin point arithmetics inside of this chip, but PCM output is strong limited to 16bit. This leads to many errors in LSBs when using DSP routings (pre cut, EQ and so on..) in 32bit format and downsampling it to 16bits output (that is why ditherin option available there)
By the way, codec already used  in X5 (TI TLV320) is ready to work with 24 bit words, but this possibilities is ommited.

Is it possible to made the "audiophile grade" build for X5 where output PCM format  from CF5250 will 24bit I2S?
Is it possible to made the "audiophile grade" build for X5 where all DSP routins wil be ommited?

saratoga:

--- Quote from: Alex_Nsk on April 10, 2009, 01:25:54 AM ---Right now I can connect X5 throu I2S@16bit bus to the my home audiophile multibit  DAC, it sounds great, but I want more audiophile sound on a walk mode...
I plannin to made a little board whith brand new audiophile DAC & powerfull headphone amp, and put it inside the X5L instead of it's second little battery.
To reach the best possible sound I'm plan to use TI PCM1798 + AD8620 buffers + TPA6120 headphones driver.  PCM1798 can work with up to 24bit*192kHz input PCM.

--- End quote ---

Neat project.


--- Quote from: Alex_Nsk on April 10, 2009, 01:25:54 AM ---So my question is: is it possible to cansel limit on 16bit PCM words output from the Coldfire CF5250? There are 32-bit floatin point arithmetics inside of this chip, but PCM output is strong limited to 16bit.

--- End quote ---

Its actually not floating point internally.  Rockbox doesn't use FP at all.  But assuming your chip can handle 24 bit words, I don't see why you couldn't output at 24 (or even 32 bit) with some changes to the code.  The playback engine would be ok with it, we currently don't just because don't have any devices with good enough DACs to take advantage of it.

Alex_Nsk:
Unfortunatelly, i just haven't any knowleges in programmin'...So, could you be patient  to help me with such modifications? I'm needed in limits of 24 bit output words, nothin' else...Just a thought: there are possible must to be changed dithering formulas??

So, technical task sound in this way: output from Coldfire chip must be in 24bit I2S format (exept of 16bit I2S novaday) for all supported input formats, regerdless it's bit depth. Doing' so all downsampling errors will be shifted to the LSB of 24bit words (256x down in amplitude).

BIG Thanks anyway!

Hey, ANYBODY???

Llorean:
Since this is something specific to your hardware modification, you're probably going to have to do the programming yourself. That means it's time to start learning. :)

saratoga:

--- Quote from: Alex_Nsk on April 12, 2009, 11:08:51 PM ---Unfortunatelly, i just haven't any knowleges in programmin'...So, could you be patient  to help me with such modifications? I'm needed in limits of 24 bit output words, nothin' else...Just a thought: there are possible must to be changed dithering formulas??

--- End quote ---

I don't know how your hardware works, so you'll have to figure that out yourself.  And if you output at 24+ bit you would disable dithering.

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