$ /home/pi/special/ffmpeg/ffmpeg -f alsa -acodec pcm_s32le -i mic_sv -c copy out.wav
ffmpeg version git-2017-02-05-e57fd92 Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 4.9.2 (Raspbian 4.9.2-10)
  configuration: --extra-cflags=-I/opt/vc/include/IL --enable-nonfree --enable-omx-rpi --logfile=CONFIG.TXT
  libavutil      55. 46.100 / 55. 46.100
  libavcodec     57. 75.100 / 57. 75.100
  libavformat    57. 66.101 / 57. 66.101
  libavdevice    57.  2.100 / 57.  2.100
  libavfilter     6. 73.100 /  6. 73.100
  libswscale      4.  3.101 /  4.  3.101
  libswresample   2.  4.100 /  2.  4.100
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, alsa, from 'mic_sv':
  Duration: N/A, start: 1487296703.290904, bitrate: 3072 kb/s
    Stream #0:0: Audio: pcm_s32le, 48000 Hz, stereo, s32, 3072 kb/s
Output #0, wav, to 'out.wav':
  Metadata:
    ISFT            : Lavf57.66.101
    Stream #0:0: Audio: pcm_s32le ([1][0][0][0] / 0x0001), 48000 Hz, stereo, s32, 3072 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
Press [q] to stop, [?] for help
size=    7860kB time=00:00:20.94 bitrate=3073.6kbits/s speed=   1x
video:0kB audio:7860kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.001267%