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Old 18th April 2006, 01:50 AM   #1
Lovan is offline Lovan  Sweden
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Default ad1896 slave or master output?

Hello everybody

I'm designing a DAC using AD1896 but I'm wondering if I should slave the output or use use it as a master with an output of 256*fs?

I will use a 24.576MHz clock and a PCM1794.

Any thoughts?

Thanks
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Old 18th April 2006, 03:31 AM   #2
Nerull is offline Nerull  United States
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Neither, lol. Don't use it. I've learned the long, hard lesson in designing a DAC and that's not a step in the right direction. Many threads discuss this.

Of course you can always try it out anyway, but most people here will not like that idea (including me).

~Tom
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Old 18th April 2006, 03:56 AM   #3
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Quote:
Originally posted by Nerull
Neither, lol. Don't use it. I've learned the long, hard lesson in designing a DAC and that's not a step in the right direction. Many threads discuss this.

Of course you can always try it out anyway, but most people here will not like that idea (including me).

~Tom

Which part don't you like?
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Old 18th April 2006, 04:10 AM   #4
Lovan is offline Lovan  Sweden
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Well since I'm doing a more general dac which needs to decode 44.1KHz ,48KHz, 96KHz...

...Or do I?
Since I'm using a CS8414 as a reciever, could I use MCK(256*fs) out from it to the PCM1794? Never thought about that...
I don't have to specify wordlength for PCM1794 do I?
That would be quite nice

Edit: damn spellingproblems
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Old 18th April 2006, 03:02 PM   #5
Nerull is offline Nerull  United States
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My post is in reference to the AD1896. I was designing a DAC and many people told me that it was not a good choice at all.

As bocka said here:
192k SRC - which is best?
The best ASRC is no ASRC.
And here:
http://www.diyaudio.com/forums/showt...341#post528341

Instead of the actual filtering of jitter, you should probably try to eliminate it at the source (this is diy after all, so you can do it! ) ; kinda like going for the hive instead of killing the individual bees.

I guess if you really wanted to, you could. Personally though, I wouldn't use it and opt for stopping jitter and gaining sound quality through a different way. I2S...a new clock...modding the crap out of a cd player...making your own cd player...I guess this is half the fun though! You learn a lot along the way.

Good luck though!

~Tom
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Old 18th April 2006, 04:35 PM   #6
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Quote:
Originally posted by Nerull
I guess if you really wanted to, you could. Personally though, I wouldn't use it and opt for stopping jitter and gaining sound quality through a different way. I2S...a new clock...modding the crap out of a cd player...making your own cd player...I guess this is half the fun though! You learn a lot along the way.

Good luck though!

~Tom [/B]

Don't believe everything you read. Some people pray to the NOS gods, so they don't believe in ASRC, period. Personally, I believe that the virtually universally-shared negative opinions of brickwall digital filters at the DAC have rubbed off on ASRC, which is almost guilty by association. These two types of filters are not the same. Furthermore, as if I needed to explain myself further, not everyone can mod their CD players, and not everyone even has a CD player anymore. I use only a SqueezeBox and SPDIF out, so another solution is needed to reduce jitter. There are many people who DO believe in ASRC, so it's really a matter of choosing who to listen to, and your own ears, of course.
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Old 18th April 2006, 05:06 PM   #7
gmarsh is offline gmarsh  Canada
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The PCM1794 only operates as an I2S slave.

I ran into an issue some time ago with the AD1896 chip - the application had to process audio at 96KHz with a DSP that could only handle slave mode input, and the box had to accept a 192KHz sample rate input.

The AD1896 can only accept sample frequencies up to MCLK/138, so if you're using the 24.576MHz as the MCLK into the AD1896 for a 96KHz master output then your maximum input sample rate is 178KHz. And if you clock the AD1896 at its maximum MCLK of 30MHz, its 256Fs master output will be 117KHz. I needed 96KHz.

My solution involved clocking the AD1896 at 29MHz with its own oscillator and putting it in output slave mode, and using the local 24.576MHz clock feeding a 74VHC393 counter to generate the 96KHz SCK/LRCLK I2S signals for both the ASRC and DSP.

So overall... if a 178KHz input sample rate limitation isn't a problem, using a 24.576MHz clock will work fine. If you need 192KHz input capability, you'll need to either use your DAC at 110KHz instead of 96 or go with the two-oscillator-and-counter system I just mentioned.

And as far as the ASRC-versus-no-ASRC argument goes, this topic has already been beaten to death in a number of threads, just search those. I'd personally go with the ASRC, but that's just my opinion after looking at a CS8416's recovered 256Fs clock on a spectrum analyzer.
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Old 18th April 2006, 05:29 PM   #8
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Gmarsh, what do you think about using CS8416/AD1896/PCM1794 with an external 24.576 crystal driving the clocks on the AD1896 and 1794? This is what I have in mind for a DAC. Also, I only plan to upsample everything to 96 kHz, as I have no 192 kHz source (nor do I plan to get one).
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Old 18th April 2006, 06:59 PM   #9
gmarsh is offline gmarsh  Canada
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Quote:
Originally posted by ezkcdude
Gmarsh, what do you think about using CS8416/AD1896/PCM1794 with an external 24.576 crystal driving the clocks on the AD1896 and 1794? This is what I have in mind for a DAC. Also, I only plan to upsample everything to 96 kHz, as I have no 192 kHz source (nor do I plan to get one).
Sounds good to me.

I've got a CS8416/AD1896/PCM1792 headphone DAC here in front of me which is almost identical, and I'm pleased with it. Though I'm using a 29.4912MHz crystal, yielding a 115.2KHz sample frequency between ASRC/DAC and allowing 192KHz digital input.
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Old 18th April 2006, 07:59 PM   #10
Lovan is offline Lovan  Sweden
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I am in a similar situation to ezkcdude. I only have a SPDIF signal(from either the PC directly spdif out or by pcm2902 spdif out)

gmarsch:
Yes the pcm1794 can only be a slave but I thought of using the clock with a divider. Thus the question if the ASRC gives a better clock than deriving av clock from the oscillator with a divider?
I also would limit myself to using only 96KHz since the implementation is a lot easier.
Maybe you could share some pictures or ideas from your project?

ezkcdude:
I'm building almost the same thing as you but with a cs8414(and a pcm2902). Maybe you could drop me a mail and we could share some thoughts?
Especially the IV-stage needs some thoughts on my side.

Thank you for your replies

PS:
Am I right in that CS8414 is limited to 96KHz output?
DS
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