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Old 12th December 2002, 05:44 AM   #1
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Default I2S Problems

I am trying to interface an S/PDIF circuit based on a Crystal CS8405 S/PDIF transmitter chip with a RioReceiver network MP3 player. However, when I tap into the I2S signals feeding the DAC on the board, I get severely distorted sound from the S/PDIF output of the Crystal circuit. One channel is distortion-free until the signal reaches a certain volume, while the other channel is severely distorted. If I reset the chip, sometimes the severely distorted channel switches. I get essentially the same results regardless of the format (right justified, left justified, I2S) chosen. I have successfully used the circuit in other applications without problems. I have also tried both buffering and straight through connections. I'm convinced all the connections are correct after triple checking them. Do I need to invert one of the signals? Which one(s)? Any ideas?

Here is link to an MP3 sample of the output.

http://www.eutronix.com/media/Garbled.mp3

Thanks,
Stu
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Old 12th December 2002, 06:25 AM   #2
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Default i2s a standard ?

altough I2S give the impression to be just a single standard,
there are 4 i2s formats.
1. Normal i2s
2. Sony
3. lsb aligned
2. msb aligned

cant tell you what you're facing here


grtz

Simon
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Old 12th December 2002, 03:46 PM   #3
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Thanks.

I do know about the various formats of I2S, however, I believe the Crystal CS8405 supports them all. The signals I am tapping into go to a BB PCM1716 DAC, so it has to be one of the formats it supports. The Crystal chip supports all of them. Anyone else have ideas?

Stu
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Old 12th December 2002, 05:37 PM   #4
jwb is offline jwb  United States
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What do you mean, you "tap into" the I2S on the board? Just branching off some wire is probably going to result in massive signal integrity problems. When I attach an oscilloscope probe to the data trace of an I2S link, the whole signal goes to hell.
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Old 12th December 2002, 05:51 PM   #5
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Yes, by "tap into" I mean soldering wires to the pads where the signals are, well actually, it's a duplicate set of pads for an alternate DAC. That method works fine on another device I use it on. I also have everything buffered as mentioned earlier. What other alternatives are there to "grabbing" the I2S signal from an existing device, other than attaching wires?

Stu
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Old 13th December 2002, 02:55 AM   #6
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The CS8405A will accept data in three formats only one of which complies with I2S standard as specified by Philips, the other two being Left and Right justified data. The PCM1716 also accepts data in three formats and as with the CS8405A each format covers 16-24 bit data.If, assuming the CS8405A is set to receive I2S data, the PCM1716 is receiving data in a format other than I2S, chaos will reign downstream of CS8405A. The LRCLK will be inverted and the sign bit and the MSB will be out of position at the very least. I would suggest you check the mode pins on the PCM1716 and confirm the chosen format if the PCM1716 is in hardware mode. If it is in software mode it is a case of trial and error.

ray
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Old 13th December 2002, 03:44 AM   #7
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Thank you for your suggestions.

I have tried all the format modes of the CS8405, using jumpers on a test board I built. Right justified doesn't seem to work at all. Left justifed and I2S work about the same (terribly as is demonstated in the link in my first post). As far as I know, the PCM1716 is operating in software mode (device uses its digital volume control). I am trying to find out from one of the engineers of the product I am interfacing with, what format is being sent to the PCM1716, but so far no luck. Besides, the Crystal chip doesn't seem to like the signal no matter what format it is set for. It seems odd to be that my circuit would work so well in one device and so poorly in another.

Frustrating!
Stu
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Old 13th December 2002, 04:20 AM   #8
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Two things.
What does the working dac setup consist of and where is the master clock for the CS8405A coming from ?

ray
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Old 13th December 2002, 04:38 AM   #9
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By working DAC, I assume you mean the one downstream of the S/PDIF signal coming from the CS8405? That would consist of a Midiman Flying Cow with Monster Cable coaxial digital interconnect. Not exactly audiophile grade, but works for testing.

The master clock is coming from a 11.2896 mHz clock derived via PLL from a 20 mHz clock. This clock and the other I2S signals are split off on the device circuit board to two sets of pads located about .25" apart, one for the PCM1716 and one for a Crystal CS4341 (unpopulated alternate DAC). I soldered a conductor from a six inch piece of 3M rainbow ribbon cable to each of the corresponding I2S pads on the CS4341 pads and routed them to my CS8405 circuit. The audio going to the PCM1716 is 44.1 kHz and the CS8405 is set to 256fs.

Should work, I don't get it!

Stu
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Old 13th December 2002, 06:39 AM   #10
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As you say the circuit should be working. The only thing I can think of at the moment are the ground connections.
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