Sound Integration

The Training Village uses the HiFiBerry DAC+ Pro HAT for audio output. Connect it directly on top of the Raspberry Pi or on top of the Main HAT if one is installed. Audio playback from within tasks is handled by the Python sounddevice library, which accesses the hardware through PortAudio → ALSA.

Why the DAC must be released from the system before use

When the DAC is set as the active audio output in the desktop environment, the operating system holds exclusive access to the device, preventing the Training Village from using it. Setting the profile to Off releases the device and makes it available for the Training Village.

Configuration

  1. Connect headphones or speakers to the DAC output.

  2. Right-click the volume icon in the top system bar and select Device Profiles. The RPi DAC Pro entry should appear in the list. Select it and set the output profile to Stereo Output.

  3. Play any audio to verify the DAC is working correctly.

  4. Once confirmed, return to Device Profiles, select RPi DAC Pro again, and set the profile to Off. The operating system will no longer use the device, leaving it free for sounddevice to access directly.

  5. Launch the Training Village and select your soundcard under SETTINGS → SOUND SETTINGS.

Note

This configuration step only needs to be done once. The “Off” profile selection persists across reboots, so the DAC will remain available to the Training Village after the system restarts.

Latency

Playing a sound has a measured latency of mean = 9.3ms and sd = 0.9 ms.

Using the sound device in tasks

Audio files are read from the project’s media directory: /village_projects/<project_name>/media. This path is configured in SETTINGS → DIRECTORY SETTINGS as MEDIA_DIRECTORY. Place WAV files there and reference them by filename only (no path needed).

The playback cycle always follows the same order:

  1. load — decodes the audio and stages it in the buffer.

  2. play — starts playback of whatever is currently in the buffer.

  3. stop — interrupts playback mid-sound.

After calling stop, the buffer is no longer valid and a new load is required before the next play.

from village.devices.sound_device import sound_device

# Option 1 — play a WAV file from the media directory
left, right = sound_device.get_sound_from_wav("tone.wav")
sound_device.load(left, right)
sound_device.play()

# To play the same sound again, load must be called again
sound_device.stop()
left, right = sound_device.get_sound_from_wav("tone.wav")
sound_device.load(left, right)
sound_device.play()

# Option 2 — generate a tone with numpy and play it
import numpy as np

samplerate = 192000          # must match SAMPLERATE setting
duration   = 0.5             # seconds
frequency  = 4000            # Hz
t = np.linspace(0, duration, int(samplerate * duration), endpoint=False)
tone = np.sin(2 * np.pi * frequency * t).astype(np.float32)

sound_device.load(tone, tone)   # identical left and right channels → mono
sound_device.play()

get_sound_from_wav validates that the WAV sample rate matches SAMPLERATE and returns both channels as float32 arrays in the range [-1.0, 1.0].

Method reference

Method

Arguments

Description

get_sound_from_wav(file)

file: filename

Reads a WAV from MEDIA_DIRECTORY, returns (left, right) arrays.

load(left, right)

numpy arrays, equal length

Stages stereo audio for playback. Pass None for a silent channel.

play()

—

Triggers playback of the loaded sound.

stop()

—

Interrupts playback.