I've installed the newest HifiBerryOS (hifiberryos-20200403-pi3.img) on my Pi3/B+.
I had to remount /boot rw to fix: dtoverlay=hifiberry-dacplusadcpro (no card detection or config via HTTP setup in HifiBerryOS?)
The card is listed correctly now:
# arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: sndrpihifiberry [snd_rpi_hifiberry_dacplusadcpro], device 0: HiFiBerry DAC+ADC Pro HiFi multicodec-0 [HiFiBerry DAC+ADC Pro HiFi multicodec-0]
I have a line level source connected to the to the DAC+ ADC Pro 3.5mm input jack.
I used arecord to capture 44100 and 48000 kHz at 16 bits (red LED turned on while recording) and loaded the resulting WAV file into Audacity (on a PC).
The recorded signal was present but very weak.
I then used alsamixer to raise the "ADC" volume to "57 [55%] [16.50dB]".
Then I tried capturing S32_LE - DOES NOT WORK
Higher sample rates (96000, 192000) - DOES NOT WORK
Recording 96000@16 worked, but I had to fix the speed in Audacity (might be an arecord or Audacity bug?)
Can you please provide proper documentation (with working examples) on the sample-rates and bit-depths that are supported and can be used to capture audio with the DAC+ ADC Pro (at least when using HifiBerryOS)?
Maybe you can also provide some help for configuring the recording levels in alsamixer... (After several experiments, I can now only record audio on the left channel with arecord)