Problems using Java to record audio using Alsa on Intel Edison

[Christofer Dutz <christofer.dutz@xxxxxxxxx>]

Hi,

I am quite new to this topic, so please forgive me if I am asking stupid questions. I did quite some searches in google, and tried all different things for about 3 full days, but I'm sort of stuck.

I setup a WM8731 chip (http://www.mikroe.com/add-on-boards/audio-voice/audio-codec-proto/) to act as a sound-card on my Intel Edison system. I tried both the approach of manually setting up the sound hardware using manual i2c commands as well as using a system driver for that chipset. In both cases it was easy to setup everything to play audio. Now I was trying to record audio via microphone. In any case all I got was silence with clicking sounds in the recording. 

As the only source and target for any audio information is one single Java application, I decided to stick to the dummy audio driver and to setup the sound chip by setting the i2c registers from inside the Java application. It worked great for the audio output. The input only produces these clicking sounds :-(

Now I dumped the settings from pactl:

Source #1
   State: SUSPENDED
   Name: alsa_input.platform-merr_dpcm_dummy.0.analog-stereo
   Description: dummy-audio Analog Stereo
   Driver: module-alsa-card.c
   Sample Specification: s16le 2ch 48000Hz
   Channel Map: front-left,front-right
   Owner Module: 1
   Mute: no
   Volume: front-left: 65536 / 100% / 0.00 dB,   front-right: 65536 / 100% / 0.00 dB
           balance 0.00
   Base Volume: 65536 / 100% / 0.00 dB
   Monitor of Sink: n/a
   Latency: 0 usec, configured 0 usec
   Flags: HARDWARE DECIBEL_VOLUME LATENCY 
   Properties:
      alsa.resolution_bits = "16"
      device.api = "alsa"
      device.class = "sound"
      alsa.class = "generic"
      alsa.subclass = "generic-mix"
      alsa.name = ""
      alsa.id = "14"
      alsa.subdevice = "0"
      alsa.subdevice_name = "subdevice #0"
      alsa.device = "0"
      alsa.card = "1"
      alsa.card_name = "dummy-audio"
      alsa.long_card_name = "dummy-audio"
      device.bus_path = "platform-merr_dpcm_dummy.0"
      sysfs.path = "/devices/platform/merr_dpcm_dummy.0/sound/card1"
      device.string = "hw:1"
      device.buffering.buffer_size = "96000"
      device.buffering.fragment_size = "48000"
      device.access_mode = "mmap+timer"
      device.profile.name = "analog-stereo"
      device.profile.description = "Analog Stereo"
      device.description = "dummy-audio Analog Stereo"
      module-udev-detect.discovered = "1"
      device.icon_name = "audio-card"
   Ports:
      analog-input: Analog Input (priority: 10000)
   Active Port: analog-input
   Formats:
      pcm

Then I created a small program to dump the settings from inside java:

Name: dummyaudio [plughw:1,0], description: Direct Audio Device: dummy-audio, 14,

  -----------------------------------
   Source Lines
  -----------------------------------
   Line.Info: interface SourceDataLine supporting 8 audio formats, and buffers of at least 32 bytes
    - Format: Sample Rate: 44100.0, Frame Size: 4, Sample Size (bits): 16, Channels: 2, Big Endian: false, Encoding: PCM_SIGNED
   Line.Info: interface Clip supporting 8 audio formats, and buffers of at least 32 bytes
    - Format: Sample Rate: 44100.0, Frame Size: 4, Sample Size (bits): 16, Channels: 2, Big Endian: false, Encoding: PCM_SIGNED
  -----------------------------------
   Target Lines
  -----------------------------------
   Line.Info: interface TargetDataLine supporting 8 audio formats, and buffers of at least 32 bytes
    - Format: Sample Rate: 44100.0, Frame Size: 4, Sample Size (bits): 16, Channels: 2, Big Endian: false, Encoding: PCM_SIGNED

So the funny thing is that Alsa is claiming to use a sample rate of 44100, but Alsa is using 48000, the rest seems to match. Is this correct?

Does anyone have an idea why all I am getting is these clicking sounds? Help greatly appreciated :-)

Chris

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