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exaU2I - Multi-Channel Asynchronous USB to I2S Interface
exaU2I - Multi-Channel Asynchronous USB to I2S Interface
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Old 20th September 2011, 08:59 AM   #751
Marek is offline Marek  Poland
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If you want to get best performace bypass CS8414 and feed AD1865 from exa directly. Best solution for glue logic is variable length shift register so you can set delay using dip switches:
http://www.datasheetcatalog.org/data...MC14557B-D.PDF
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Old 20th September 2011, 09:06 AM   #752
Painkiller is offline Painkiller  Norway
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Quote:
Originally Posted by Marek View Post
If you want to get best performace bypass CS8414 and feed AD1865 from exa directly. Best solution for glue logic is variable length shift register so you can set delay using dip switches:
http://www.datasheetcatalog.org/data...MC14557B-D.PDF
Have you had any experience with these variable shift registers? It seems like they are quite slow devices. Rise time of 100ns, and a 300ns propagation delay. Could it really be useable for audio? I've never seen anyone use these. The 74HC series are really fast though. Single digit rise time and propagation delay.
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Old 20th September 2011, 09:11 AM   #753
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Probably the clipping comes about because the word clock (frame clock) is in the wrong phase relationship with the data. Every bit position shift in this clock results in a 6dB gain or attenuation, depending on the direction its shifted. I get great clipping effects on my DACs when the LSB of one sample gets mistaken for the MSB of the subsequent one

<edit> A good way to keep the noise down (and hence sound quality up) is to run the HC logic at low supplies - 3V is plenty fast enough for most audio.
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Last edited by abraxalito; 20th September 2011 at 09:14 AM.
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Old 20th September 2011, 09:27 AM   #754
Marek is offline Marek  Poland
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Painkiller,

I didn't try it yet, but yes it seems that delay could be a problem. The 74HC works for sure but it isn't so comfortable.
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Old 20th September 2011, 09:44 AM   #755
Painkiller is offline Painkiller  Norway
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Originally Posted by abraxalito View Post
Probably the clipping comes about because the word clock (frame clock) is in the wrong phase relationship with the data. Every bit position shift in this clock results in a 6dB gain or attenuation, depending on the direction its shifted. I get great clipping effects on my DACs when the LSB of one sample gets mistaken for the MSB of the subsequent one
Yes! That's exactly what's happening. It all makes sense. The timing requirements for the AD1865 are a little different than the I2S spec. I have to delay the LRCK by one bitclock cycle. Any ideas for a simple solution for this?
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Old 20th September 2011, 09:52 AM   #756
Marek is offline Marek  Poland
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you have to dalay DATA line and definetely not 1 cycle.
The advantage of this solution is that don't introduce any jitter on clock lines because you feed oryginal clocks to AD1865 directly.
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Old 20th September 2011, 10:21 AM   #757
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by Painkiller View Post
I have to delay the LRCK by one bitclock cycle. Any ideas for a simple solution for this?
I2S has the phase of the LRCK advanced by one bit position, so yes if you want a clock which toggles after the LSB you just need a one bit time delay. A 74HC74 flip-flop will do that well enough - its clocked from the BCK and the LRCK goes into the D input. It has both polarities of the delayed LRCK available at its outputs which often comes in handy
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Old 20th September 2011, 10:46 AM   #758
Painkiller is offline Painkiller  Norway
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I2S has the phase of the LRCK advanced by one bit position, so yes if you want a clock which toggles after the LSB you just need a one bit time delay. A 74HC74 flip-flop will do that well enough - its clocked from the BCK and the LRCK goes into the D input. It has both polarities of the delayed LRCK available at its outputs which often comes in handy
That sounds like a simple solution. My local supplier has the 74hc74 in stock, so I could pick it up tonight and make a quick fix.

I'm planning on making a AD1862 based diy dac from scratch, so this e-bay dac is sort of a test project to see if I can make the signal from the exaU2I work. The AD1862 and the AD1865 have the same timing requirements.

Thanks a lot for the help! I'm new to this digital logic stuff, so all your answers are appreciated.
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Old 20th September 2011, 11:08 AM   #759
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Its worth keeping a tinkering supply of logic on hand so you can quickly fix problems when the supplier's closed or happens to be out of stock. 74HC74 and 74HC02 are jolly useful to have around, as are 74HC595 and 74HC4053.
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Old 20th September 2011, 11:25 AM   #760
Marek is offline Marek  Poland
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You still forget that AD1865 is 18-bit DAC and what you need to delay is not LRCLK but DATA line by 32-1-18 cycles...

Last edited by Marek; 20th September 2011 at 11:28 AM.
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