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Old 4th September 2012, 05:05 PM   #291
1audio is offline 1audio  United States
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I have that demo board as well. Let me reconnect it and compare the results.
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Old 4th September 2012, 06:14 PM   #292
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Default PCM4222 EVM

Here is the same source measured with the PCM4222 EVM. I did not get the same results or even nearly so as the linked test. Distortion products are higher. Key difference- I am sampling at 192 KHz. Changing the sample rate is a real PITA on these. I had to get the local FAE to get the board running and he had to call several people at TI for guidance.

It also shows me that I have some jitter in the on board clocking on the AKM board (its not well done and I should completely reconstruct it).

The noise above the oscillator frequency is lower than the noise below (??). The noise shaping start up at 50 KHz on this chip. I'll leave it running and recheck the distortion in a few hours to see if its better. I also need a better power supply for these guys.
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Old 4th September 2012, 06:19 PM   #293
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OK, thanks. I was planning on battery power. I'd be interested to know if there's a better ADC out there.

How did you get the signal into your computer? Did you use the S/PDIF RCA jacks or the AES jacks? I bought a miniStreamer from miniDSP that is a bidirectional I2S to USB link, since I only have USB available on my laptop.
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Old 4th September 2012, 06:37 PM   #294
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I'm using SPDIF coax to a Juli@ card. I am also using an external OXCO 24.576 oscillator with really low jitter. The Ministreamer would be a good choice. Those guys are very good. The demo boards support I2S and I think you can configure the Ministreamer so the clock schemes will work.

For ADC use there is very little possible difference between AES and SPDIF since the information is not time critical data like the DAC side.
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Old 4th September 2012, 06:54 PM   #295
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RE PCM4222: Things I'm not crazy about -- that bundle of trash at around 48kHz, which has been an issue for me with the EMU 0204, too. Is that actually from the ADC? And the higher distortion with lots of products way on out....
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Old 4th September 2012, 07:12 PM   #296
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Quote:
Originally Posted by 1audio View Post
I'm using SPDIF coax to a Juli@ card. I am also using an external OXCO 24.576 oscillator with really low jitter. The Ministreamer would be a good choice. Those guys are very good. The demo boards support I2S and I think you can configure the Ministreamer so the clock schemes will work.

For ADC use there is very little possible difference between AES and SPDIF since the information is not time critical data like the DAC side.
Someone mentioned the advantages of using balanced connections for test and measurement. I wonder if the balanced AES signal would be cleaner?

Also, how would I interface the balanced inputs of the evaluation board with a single ended circuit?
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Old 4th September 2012, 08:31 PM   #297
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Quote:
Originally Posted by richiem View Post
RE PCM4222: Things I'm not crazy about -- that bundle of trash at around 48kHz, which has been an issue for me with the EMU 0204, too. Is that actually from the ADC? And the higher distortion with lots of products way on out....
Maybe they were not enclosed in a good RFI proof box?
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Old 5th September 2012, 03:08 AM   #298
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Default RFI Shielding?

Not really. The generator is in the stack on the left under the aluminium chassis and the ADC is on the right on top of the Heathkit supply connected through 8 feet of coax. Its identical to the setup used with the AKM demo board. Neither are particularly good.

The big board in front is what I should be working on. . .
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Old 5th September 2012, 04:23 AM   #299
richiem is offline richiem  United States
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The bundle of modulated spikes at 48kHz has nothing to do with EMI or RFI -- it's something from the ADC or the interface, and since I see the same thing in the EMU 0204 with a different interface, I think it's the ADC.
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Old 5th September 2012, 02:16 PM   #300
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The bundle of modulated spikes at 48kHz has nothing to do with EMI or RFI -- it's something from the ADC or the interface, and since I see the same thing in the EMU 0204 with a different interface, I think it's the ADC.
Well, I doubt you're going to find something better that doesn't cost the moon. I've been looking at various sound cards and USB/Firewire interfaces for pro audio and none seem to have lower noise. The M-Audio and Focusrite products seem to be popular and well regarded, but don't know for sure. Do you have any suggestions for a better ADC/DAC? I checked National Instruments and they only have 16 bit interfaces.

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