Oversampled TDA1541(a) I2S format? - Page 2 - diyAudio
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Old 13th April 2006, 01:07 PM   #11
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Default oh is that all

Ulas,

It might be interesting but after all that manipulation of the data wouldnt you get a lot of jitter / other timing problems?

Plus I barely understand what you just wrote!

For me the phrase "descretion is the better part of valor" is definately applicable! As a first DAC project it seems unwise. I see scrap

Unfortunately I would like to know how it was done, even if I dont use that knowledge - its like alternative therapy...

Andy
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Old 13th April 2006, 02:25 PM   #12
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Default Re: oh is that all

Quote:
Originally posted by andrew_whitham
It might be interesting but after all that manipulation of the data wouldnt you get a lot of jitter / other timing problems?
What is this obsession with jitter? There is only one place in the D/A conversion process where jitter matters and that is the moment the analog output changes to reflect the value of the next sample.

Do you have any idea how many gates and latches there are in a CS8414/DF1704/TDA1541 combo, not to mention what goes on in the CDP, and before that, all the gates and latches the signal goes through in the recording and mastering process. If all that seems to work OK, how can the addition of a few more gates and latches necessarily screw it up? If every clocked digital circuit were plagued with jitter, as you seem to think, computers wouldn’t work and we sure as hell wouldn’t be communicating via the Internet.
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Old 14th April 2006, 05:16 AM   #13
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Default Re: Re: oh is that all

Quote:
Originally posted by Ulas


What is this obsession with jitter? There is only one place in the D/A conversion process where jitter matters and that is the moment the analog output changes to reflect the value of the next sample.
Admittedly, I've been banging my head against a brick wall about that. I'm avoiding it or anything that *might* cause the clock / data to get shuffled beacuse I dont yet fully understand its effects that's all... Sounds like I'm giving it more room than necessary.

But since there's be more mileage in this than I'd thought, I see why you delay the data a BCK half cycle (rising edge vs falling edge yes?) and I can see where the LE signal would be derived from, but why invert the MSB?

I have some reading to do...

or some plagiarisim to do
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Old 14th April 2006, 06:10 AM   #14
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Default Re: Re: Re: oh is that all

Quote:
Originally posted by andrew_whitham
but why invert the MSB?
To convert from offset binary to two's complement.

Combining the timing diagrams of each chip on a single page helps clarify the relationships.
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Old 14th April 2006, 06:43 AM   #15
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Default blimey this is tricky.

I think we're at cross purposes

I was thinking the data has to go into the tda1541a using simultaneous mode (data left + data right). which is already offset binary.

I need therefore, to convert from "Binary twos compliment, MSB first, right justified audio data" to offset binary? And I think thats the timing charts below? (assuming I cut the right bits from the datasheets)

Actually the whole i2s aspect of this may have been an error. The i2s input on the TDA1541 is rated at 4x oversampling where the DF1704 only outputs at 8x.

Andy
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Old 14th April 2006, 01:03 PM   #16
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Default Re: blimey this is tricky.

Quote:
Originally posted by andrew_whitham
I was thinking the data has to go into the tda1541a using simultaneous mode (data left + data right). which is already offset binary.
Right, just a typo. Which ever direction you want to go, binary offset to or from two's complement, you just invert the MSB.

The TDA1541A is spec'd for 8X.
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Old 14th April 2006, 03:13 PM   #17
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Sorry to intrude...

Andy, why don't you just connect I2S to your DAC chip and see if you like it???
(sorry rfbrw)

I'm always the first to recognize that I know nothing but I recently succeeded to make my first nonos DAC (yes, with the veteran 1543*4) from scratch, directly fed through I2S and I'm very happy with the result. Not the ultimate in detail but engaging and satisfactory.

Don't get mad at me, I'm only trying to help

Good luck
M

PS: what I2S capable transport are you using? I would love to find some cheap I2S transports
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Old 14th April 2006, 06:48 PM   #18
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Quote:
Originally posted by maxlorenz

Don't get mad at me, I'm only trying to help
I imagine Tomas de Torquemada said something similar when he was trying to convert someone.
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Old 15th April 2006, 12:16 AM   #19
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Quote:
I imagine Tomas de Torquemada said something similar when he was trying to convert someone.
LOL. You got me there

I love you, man

Ciao
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Old 15th April 2006, 06:53 AM   #20
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Maxlorenz

no I2S is actually available I was confusing Phillips 2's compliment with Burr-Browns, a fairly impressive demonstration of knowing nothing..

So aside form the thread's title I'm now just trying to figure out how you might link the two - filter to DAC - but my logic isnt that sharp.

Congrats on your dac, I dont know of any I2S 'transports' out there but, wouldnt any of the old philips players be i2s friendly. Anything shipping with a 1543 in it has to have i2s in there somewhere. right? And you can pick those up cheap!
(you'd also get a free oversampling filter )

Andy
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