I'm having a similar problem.... How was this resolved? ~Trying to figure out your postings.
Here is my posting: https://groups.google.com/forum/#!category-topic/beagleboard/beaglebone-capes/sZUt7B1tNi8 On Saturday, October 19, 2013 at 11:12:48 AM UTC-4, Hussein Alasadi wrote: > > I guess you mean the highpass filter? That should solve your issue. > > Under alsamixer you should find a setting for the builtin highpass filter. > Setting it to anything other than disabled (0.0045xFs or so was the first > option) will get rid of the DC offset. > > Regards > Hussein > > On Wednesday, October 9, 2013 4:05:05 AM UTC+2, Tim R. wrote: >> >> Hello All! >> >> I'm using the Beaglebone Audio cape to record audio samples with my >> Beaglebone Black running the 3.8.13-bone28 kernel on Ubuntu 12.04. After >> disabling the HDMI 'virtual cape' disabled, upgrading to the bone28 kernel >> and cloning the BB-BONE-AUDI-01-00A0.dtbo firmware for my A1 version Audio >> cape I was able to get the cape initialized + working. >> >> I'm now trying to figure out why there is a DC offset n the recorded >> audio for both channels of this board. Recording silence using arecord >> shows a clear and constant non-zero level on both the left and right >> channels. Similarly when inputting a small test tone signal I can clearly >> see in the recorded audio the signal offset from zero by the same amount >> that as in the silence recording. >> >> I thought I was seeing things so I connected a digital multimeter to the >> inside of the AC coupling capacitors (C50 and C51 from the Audio Cape >> schematic) while recording and I read a constant 1.34V. When I stop the >> recording the voltage drops to around 100mV. So there is some kind of DC >> signal on the input to the DAC. I have two audio capes and both show this >> behavior so I'm guessing this is not a manufacturing flaw in my audio cape. >> >> There is an easy workaround available by turning on the TLV320AIC3106's >> built-in low-pass filter. By doing this I was able to eliminate the >> DC-level in the resulting audio files. I can see the level drop to zero >> exactly when I issue the I2C writes to turn on the low-pass filter. >> Unfortunately this is only a work-around because the driver for >> the TLV320AIC3106 resets the I2C registers every time the audio device is >> activated. This means I can't just run this once on startup and forget >> about this issue. It's also non-optimal because there are effectively two >> low-pass filters in the signal path - the AC coupling capacitor and the >> low-pass filter within the codec which means that low-frequency components >> in the audio signal will be attenuated twice. >> >> Has anyone noticed this issue? Is there a known solution out there I am >> not aware of? >> >> Thanks in advance for any help or ideas. >> >> Thanks! >> >> Tim >> > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
