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Old 11th September 2011, 02:54 PM   #1
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Default DCX2496 ASRC question

Been testing my DCX2496 with various SPDIF/TOSLINK inputs, and have had mixed results. Wondering if it is possible to tap into I2S, if it's even available at this stage in the DCX (prior to DSP).

My thought was to use a an external USB/I2S ASRC converter and tap into the output of the existing CS8420. It is not easy to understand the data sheet of the CS8420; I know it has I2S capability but not sure what it's set up for.

Would this address any jitter problems that I current have with SPDIF inputs? I am not familiar enough with I2S to fully understand what I am gaining, but my understanding is it corrects the input signal perfectly, thereafter only being subject to the system clock to which it is feeding.
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Old 11th September 2011, 03:03 PM   #2
Pano is offline Pano  United States
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There are a number of clock kits and mods for the DCX. You could look into those either as a turnkey solution or as inspiration for your own if you want to get a lower jitter signal into the ASRC.

BTW, what sort of problems are you having with the digital input? It's AES, but tends to work OK with unbalanced SPDIF in. There is not Toslink, unless you've added one.
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Old 11th September 2011, 08:00 PM   #3
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Yes, I've read about all the clock mods on the DCX. Thing is, my problem appears to be with the quality of my SPDIF input, not with the internal clock on the DCX.

What I found is by ear and measurement various sources resulted in significant difference with analog output quality. An AppleTV's toslink in combination with Twisted Pear's converter was the worst (no fault of TP, I believe). A MacBookPro's toslink was improved quite a bit, with only a few glitches here and there (sounds like a hiccup in the audio stream). Finally, my M-Audio SPDIF is essentially perfect, so my assumption is I am dealing with an issue of SPDIF quality.

I would rather not have to use my M-Audio for a source, so need to consider a source with an appropriate converter that eliminates the SPDIF quality problem. I could use a Mac Mini, which has USB output.

The recent thread on the FIFO is interesting, but doesn't seem to really be going anywhere. Bypassing the CS8420 entirely is a consideration, but I don't know how difficult that is.
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Old 19th September 2011, 12:13 AM   #4
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What about installing one of the MiniDSP Ministreamers with the possibility of using the I2S output, bypassing the CS8420 entirely?

miniSTREAMER | miniDSP

I could try to post at the MiniDSP forum if that makes more sense. $55 seems reasonable if I can get I2S, using the internal clock on the DCX.
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Old 19th September 2011, 08:01 AM   #5
zoka959 is offline zoka959  Serbia
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zigzagflux,
I am also interested in bypassing cs8420 in behringer with I2S input,
so I watch this thread with care.
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Old 19th September 2011, 01:21 PM   #6
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Scratch that idea; if I bypass the CS8420 and go I2S, I will need to ensure a 96 kHz stream, which I don't have. Since the MiniStreamer does not upsample, all I can do is use the SPDIF output and keep the CS8420. But if the SPDIF is improved over my existing sources, that is fine too.

What can be expected of jitter quality with the MiniStreamer, or for that matter anything that runs USB to SPDIF? Not familiar enough with what goes on in those products.
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Old 21st September 2011, 07:00 AM   #7
zoka959 is offline zoka959  Serbia
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Zigzagflux,
go on this thread I have very valuable answers
XMOS-based Asynchronous USB to I2S interface
Hope it will help
Zoran
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Old 22nd September 2011, 04:40 PM   #8
qusp is offline qusp  Australia
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it sounds to me like your hiccups are probably caused by incorrectly setup device drivers wrt buffer size
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Old 22nd September 2011, 05:26 PM   #9
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It would not surprise me; to be honest I wouldn't even know how to change things around to test this. You would think running optical out of a MBP would be driverless in a sense. What options do I have to change this? I can go into the AudioMidi app and change bit number and freq, but that didn't seem to make a difference (either worked or it didn't).

After further reading, it looks like the CS8420 is set up in hardware mode 1. Output is slave I2S 24 bit, which makes sense. Mode is 1A, which I don't understand. I would be interested in going to hardware mode 2, but this requires a number of board level changes to the CS8420 pins. Serial input can be set for I2S with IF2 setting. There is also a CUVEN choice that I don't understand. So it certainly looks possible, but would take someone with more knowledge than I to make sure compatibilities are sound.
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Old 21st November 2011, 08:03 AM   #10
kotani is offline kotani  Japan
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Quote:
Originally Posted by zigzagflux View Post
Scratch that idea; if I bypass the CS8420 and go I2S, I will need to ensure a 96 kHz stream, which I don't have. Since the MiniStreamer does not upsample, all I can do is use the SPDIF output and keep the CS8420. But if the SPDIF is improved over my existing sources, that is fine too.
I may be a little late in responding, but wouldn't the twisted pear Metronome fit the bill? You can convert he incoming I2S signal to a constant 96khz, effectivly bypassing the CS8420. Please let me know if it is possible, as I would be very much interested in building a i2s in, i2s out dcx2496 to feed three external dacs...

link for Twisted Pear Metronome:
The Metronome ASRC Module
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