ADC DC offset freeze problem

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hopkins
Posts: 1
Joined: Wed Sep 06, 2017 10:53 pm

ADC DC offset freeze problem

Post by hopkins » Wed Sep 06, 2017 11:29 pm

Hi, I received my octo card yesterday, 5 Sept 2017, and got it working for six channel audio input ok using both arecord and audacity. However I intend to measure down to DC(using differential preamp offsetting and bypassing the analogue filters) and whilst experimenting with FREEZE to lock the DC offset in the mixer found that ADC channels 1 to 4 seem to work ok(though I've not done calibration checks yet) Channels 5 and 6 go unstable. I've checked the cirrus 'CS42xx8.c' file in the linux rpi kernel source and note that the adc-DC-freeze process only changes bit 7 of the chip's Register 5 (The ADC control register) but the data manual for the chip indicates that there are two freeze bits - - bit 7 for ADC 1 and 2, and bit 6 for ADC 3 (ie ch5 and ch6) Can you see any problems if I add the bit 6 freeze code to the codec and recompile - I don't know the details of how the octo card communicates with the Rasp Pi. There may be some restrictions Thanks, Irvin Hopkins

flatmax
Posts: 609
Joined: Sat Jul 23, 2016 11:39 pm

Re: ADC DC offset freeze problem

Post by flatmax » Sat Sep 16, 2017 1:49 pm

I would be very interested to hear the outcome of this.

I can't see any problem in experimenting with it ...

Do you need any info / help ?

Matt
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