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3.5mm Audio Jack

1. Introduction​

The RK3506B connects to an external audio codec, the ES8311, via I2S and I2C interfaces to enable audio recording and playback. It supports microphone input and headphone output, meeting the requirements for high-quality audio processing.

2. Audio Configuration​

  1. Check available sound card devices

    root@luckfox:~# arecord -l
    **** List of CAPTURE Hardware Devices ****
    card 0: rockchipes8311s [rockchip,es8311-sound], device 0: ff310000.sai-ES8311 HiFi ES8311 HiFi-0 [ff310000.sai-ES8311 HiFi ES8311 HiFi-0]
    Subdevices: 1/1
    Subdevice #0: subdevice #0

    root@luckfox:~# aplay -l
    **** List of PLAYBACK Hardware Devices ****
    card 0: rockchipes8311s [rockchip,es8311-sound], device 0: ff310000.sai-ES8311 HiFi ES8311 HiFi-0 [ff310000.sai-ES8311 HiFi ES8311 HiFi-0]
    Subdevices: 1/1
    Subdevice #0: subdevice #0

    • card0: Refers to the ES8311 audio codec.

  2. Driver nodes for the sound card

    root@luckfox:~# ls /dev/snd/
    by-path    controlC0  pcmC0D0c   pcmC0D0p   timer
    • controlC0: Used for sound card control, where C0 refers to card 0, corresponding to the ES8311 audio output mentioned above.
    • pcmC0D0c: The pcm device used for recording. The c stands for capture.
    • pcmC0D0p: The pcm device used for playback. The p stands for playback.
    • by-path: Stores device mapping information.
    root@luckfox:~# ls -l /dev/snd/by-path/
    total 0
    lrwxrwxrwx    1 root     root            12 Jan  1 00:00 platform-es8311-sound -> ../controlC0

3. Recording​

  1. Record audio in WAV format at 16kHz sampling rate, 2 channels, 16-bit:

    arecord -D hw:0,0  -t wav -d 10 -f S16_LE test.wav
    • -f S16_LE: Specifies 16-bit little-endian PCM format
    • -r 16000: Sets the sample rate to 16 kHz
    • -D hw:0,0: Selects card 0, device 0
    • -d 10: Duration of recording in seconds
    • test.wav: Output filename

  2. If no sample rate is specified, arecord defaults to 44100 Hz (CD quality).

    arecord -f cd -Dhw:0 -d 30 test.wav

4. Playback​

  1. Play audio in WAV format:

    aplay test.wav

5. Volume Adjustment​

  1. Adjust headphone volume (recommended)

    amixer -c 0 sset 'DAC VOLUME' 50%
    • Recommended range: 40%–70%
    amixer -c 0 cset name='DAC VOLUME' 150
    • Recommended range: 100–180

  2. Adjust volume using SoX

    # Check the maximum volume adjustment factor
    # sox anheqiao.wav -n stat
    Samples read:          22058820
    Length (seconds):    250.100000
    Scaled by:         2147483647.0
    Maximum amplitude:     0.891235
    Minimum amplitude:    -0.891266
    Midline amplitude:    -0.000015
    Mean    norm:          0.153542
    Mean    amplitude:    -0.000068
    RMS     amplitude:     0.206771
    Maximum delta:         1.232666
    Minimum delta:         0.000000
    Mean    delta:         0.060496
    RMS     delta:         0.092891
    Rough   frequency:         3153
    Volume adjustment:        1.122

    ## Adjust volume by applying a scaling factor, creating a new file
    sox -v 0.2 anheqiao.wav output.wav
    • SoX (Sound eXchange) is a powerful audio processing tool. Note that some features, such as MP3 encoding, may require specific build options or external libraries.