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Audio and Recording

The Walnut Pi 2B supports both HDMI audio and 3.5mm headphone jack audio output.

HDMI Audio​

If your HDMI display has built-in speakers, you can verify this by connecting it to a Windows computer. If you can select audio output and hear sound, the HDMI display supports audio.

Viewing Audio Devices​

Use the following command to view HDMI audio information:

aplay -l

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Audio Playback Test​

Test by playing a built-in WAV audio file. The ahubhdmi in the command below is the HDMI audio device name found from the command above: (Note: this command uses [plughw] instead of [hw] as used for the headphone jack.)

aplay -D plughw:hdmi /usr/share/sounds/alsa/Noise.wav

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Desktop Edition Music Playback​

You can directly use the pre-installed VLC media player on the Desktop edition to play audio. The Walnut Pi system defaults to the headphone jack for audio output. Simply switch to HDMI in the bottom-right system tray to globally switch the audio output for players, browsers, etc.

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First, copy audio files to the Walnut Pi via USB drive or SSH, then right-click and select Open with VLC Media Player:

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3.5mm Headphone Jack​

The back of the Walnut Pi 2B has an audio FPC connector, which can be adapted to a 3.5mm audio jack (the common headphone jack) using an adapter board. This can be used to connect headphones or speakers for louder sound output.

Note:

The Walnut Pi 2B's 3.5mm audio output jack has a certain output power and can drive both headphones and powered speakers.

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Viewing Audio Devices​

Use the following command to view audio device information:

aplay -l

audio1

Audio Playback Test​

Test by playing a built-in WAV audio file. The audiocodec in the command below is the headphone jack device name found from the command above:

aplay -D hw:audiocodec /usr/share/sounds/alsa/Noise.wav

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Connect headphones or speakers to the audio jack to hear the sound.

Desktop Edition Music Playback​

You can directly use the pre-installed VLC media player on the Desktop edition to play audio.

First, copy audio files to the Walnut Pi via USB drive or SSH, then right-click and select Open with VLC Media Player:

audio3

Recording​

The Walnut Pi can use a USB microphone as a recording input device. This tutorial uses the following common Raspberry Pi USB microphone:

Note

The Walnut Pi 2B requires image version V1.1.0 or later.

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Plug the USB microphone into any USB port on the Walnut Pi.

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Use the following command to identify the USB microphone device:

lsusb

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The following command lists audio devices:

arecord -l

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Recording Test​

You can record using the following command:

arecord -D "plughw:2,0" -f S16_LE -r 16000 -d 10 -t wav test.wav
  • -D: Device name. From arecord -l above, this is card2, device0. Use: "plughw:2,0";
  • -f: Recording format. S16_LE means 16-bit;
  • -r: Sample rate. 16000 means 16 kHz;
  • -d: Recording duration. 10 means 10 seconds;
  • -t: File format. wav means WAV format;
  • test.wav: Generates a test.wav file in the current directory.

After recording, you will see the generated test.wav file in the current directory:

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You can play it back through the audio jack with the following command:

aplay -D hw:audiocodec test.wav

Adjusting Microphone Volume​

The default microphone volume may be low. You can adjust it as follows:

Enter the following command:

alsamixer

In the pop-up interface, press F6 and select the USB microphone.

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Then press F5, and use the mouse or keyboard arrow keys to select MIC:

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Use the keyboard up and down arrow keys to adjust the volume. Press ESC to exit when done.

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Run the recording command again, and you should hear a change in the recorded audio volume.

Note

If you are using the Desktop edition, you can directly adjust the microphone volume via the audio icon in the bottom-right corner. audio