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seeb  
#1 Posted : Tuesday, February 12, 2013 2:12:30 AM(UTC)
seeb

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I'm connecting an Opus to a BeagleBoard-xM via 16 bit I2S. I used a 74AVC4T245 to translate the BB's data out, frame sync and bit clock from 1.8v to 3.3v. Signals going into the Opus look OK. The Opus DIP switches are set to off except for TXSRC which is on. I was unable to get any sound out via SPDIF (monitoring via an MAudio SuperDAC 2496) until I connected the Opus' CLOCK to SCK. After doing that the right channel sounds correct but the left channel has intermittent clicks mixed in that appear to be audio data dependent. The BB's built in audio that is driven from the same I2S sounds OK. I inverted the frame sync to the Opus but the clicks stayed on the left channel. I am playing WAV files from GNOME MPlayer to test the setup. There are no clicks when the WAV file's left channel data is all zeros. If I play a WAV file with a low level square wave on the left channel (values of 0x0001 and 0xFFFF) I hear random clicks. The data on the right channel has no effect on the left channel clicks.

Do I have this configured properly? Could there be an issue with the Opus? Any help appreciated.
Russ White  
#2 Posted : Wednesday, February 13, 2013 11:12:32 PM(UTC)
Russ White

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Do you have another source to test with?
seeb  
#3 Posted : Wednesday, February 27, 2013 7:55:29 PM(UTC)
seeb

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I don't have any other sources of I2S handy at the moment, but here's what I found. It seems at least for hardware mode that I2S in to SPDIF out requires SCK to be at 256FS, as opposed to the internally generated 12MHz clock that I had previously looped to SCLK. The left channel works properly when I connect an external 256FS generator to SCLK. I'll likely need to use the serial port to configure advanced settings, or add an external PLL/divider circuit to derive a 256FS clock from LRCLK or BCLK.
Russ White  
#4 Posted : Wednesday, February 27, 2013 11:31:32 PM(UTC)
Russ White

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Yeah I would get a good quality clock multiplier and just multiply the bit clock up to the required master clock frequency.
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