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idle tones at 6k and 12k with ADAU1701 and firewire soundcard combi

Question asked by StefanGrob on Apr 15, 2014
Latest reply on Apr 21, 2014 by ColemanR

Hello,

 

I'm measuring 6k and 12k idle tones on all audio outputs only when my ADAU1701 board gets it's clocks from an OEM Firewire soundcard. As long as I use the on board clocks, audio is clean.

20140415 idle tones ADAU1701andAF12.PNG

 

The hardware configuration is quite complex, MP0 til MP6 are connected to the soundcard with I2S

At fs=48kHz,  MCLK is 12.288MHz, BCLK is 3.072MHz, LRCK is 48 kHz

The serial output is used as (slave) TDM bus to an 8 channel DAC, MP10 (LRCK) is 48kHz and MP11 (BICK) is 12.288MHz. The idle tones can be heard on the outputs of the TDM DAC as well.

All clock signals are derived from the OEM soundcard, the soundcard is the master.

 

If I change the soundcards sample frequency, the idle tones scale with it, so I expect the clock signals to be the cause. Any suggestions?

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