Audio

Copyright © Quectel Wireless Solutions Co., Ltd. 2026. All rights reserved.

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This document provides a concise guide to operating the Linux audio system on the Quectel Pi M2 development board (RK3576 platform). The system adopts an ALSA + PipeWire (PulseAudio-compatible) audio architecture, delivering a complete audio solution from the low-level drivers to the application layer.

Quick Start

The Quectel Pi M2 development board is based on the Rockchip RK3576 platform. The audio codec is the Everest ES8389 (I2S interface, I2C address 0x10). The audio hardware comprises 4 types of channels:

Channel Type	Channel Name	Hardware Location	Description
Input	Onboard MIC	Onboard MEMS microphone	Built-in silicon microphone; default recording input source; no external connection required
Input && Output	Headset	3.5 mm headset jack	Supports national-standard/US-standard headsets, with headset insertion detection (ADC-based). When a headset is plugged in, the system automatically switches the playback path to the headset (and disables the speaker PA); when it is unplugged, playback switches back to the speaker automatically
Output	SPK (Speaker)	Speaker connector	Onboard amplifier (PA); speaker output by default, DAC defaults to -6 dB. Shares the same DAC audio source with the headset (both connect to HPOL/HPOR); output is controlled only through the PA enable (spk-con-gpio)
Output	HDMI Audio	HDMI connector	Outputs digital audio via HDMI (sound card rockchip-hdmi)
Output	Bluetooth Audio	Bluetooth antenna	A2DP playback on Bluetooth speakers/headsets; HFP hands-free calls

The system provides a set of standard audio configuration and debugging commands for common operations such as device inspection, recording, playback and volume control.

Audio architecture note: The Debian system on the M2 development board uses PipeWire + WirePlumber as the audio service (replacing the traditional PulseAudio) and provides PulseAudio-compatible command-line tools such as pactl/paplay. The sound-card hardware is still driven by ALSA underneath.

Checking Sound Card Information

Use the following commands to check the loaded sound cards and PCM devices on the system:

• View the sound card list:

cat /proc/asound/cards

Expected output (M2 development board):

 0 [rockchipes8389 ]: rockchip-es8389 - rockchip-es8389
                      rockchip-es8389
 1 [rockchipbt     ]: simple-card - rockchip,bt
                      rockchip,bt
 2 [rockchiphdmi   ]: rockchip-hdmi - rockchip-hdmi
                      rockchip-hdmi

• View the list of allocated PCM streams:

cat /proc/asound/pcm

• View the current default audio devices:

aplay -l
arecord -l

Note: If the system does not detect any sound card information or PCM stream, neither ALSA nor PipeWire can work properly.

ALSA Architecture

ALSA Overview

ALSA is the low-level audio architecture and driver core of the Linux system; it directly manages and controls the audio hardware. The kernel of the M2 development board already includes the ES8389 codec driver (sound/soc/codecs/es8389.c) and the machine driver (sound/soc/rockchip/rockchip_multicodecs.c). The sound card is defined in the device tree file rk3576-quectel-pi-m2-audio.dtsi:

• ES8389 codec: I2C address 0x10, MCLK 12.288 MHz, connected via the SAI1 (I2S) interface

• Headset detection: hp-det-gpio + SARADC detection; supports automatic switching on headset insert/unplug

• Speaker amplifier: spk-con-gpio (speak_pa_en) controls the PA enable

• MIC input source switching: rockchip,mic-source-switch supports switching between the onboard MIC and the headset MIC

• HDMI audio: sound card rockchip-hdmi, connected via the SAI6 interface

Main ES8389 ALSA Controls

All ES8389 controls can be viewed and set with amixer:

amixer -c 0 scontrols

Commonly used controls:

Control Name	Description	Default Value
DACL Playback Volume	Left-channel DAC volume (0~255, 191 = 0 dB, 0.5 dB/step)	179 (-6 dB)
DACR Playback Volume	Right-channel DAC volume (0~255, 191 = 0 dB, 0.5 dB/step)	179 (-6 dB)
ADCL PGA Volume	Left-channel microphone PGA gain (0~14)	8
ADCR PGA Volume	Right-channel microphone PGA gain (0~14)	8
Speaker	Speaker switch (DAPM control)	on
Headphone	Headphone switch (DAPM control)	on

Note: The default speaker volume on the M2 development board is -6 dB (DAC = 179), fixed through the ALSA path configuration file (/usr/share/alsa-card-profile/mixer/paths/analog-output-es8389-m2.conf) to prevent the speaker from being too loud. To adjust it, modify the volume = 179 value in this configuration file (e.g. 185 for -3 dB, 173 for -9 dB), or adjust it temporarily with amixer.

Audio Recording

Onboard Microphone Recording

Default recording input source auto-switching rule: The system monitors the headset plug/unplug state in real time through headset insertion detection (hp-det-gpio + SARADC) and automatically switches the recording input source:

• Headset plugged in: recording uses the headset microphone by default; no manual switching is required

• Headset not plugged in: recording uses the onboard MIC by default

When no headset is plugged in, the default recording input source of the M2 development board is the onboard MIC. Record with arecord:

arecord -D hw:0,0 -f S16_LE -r 48000 -c 2 -d 5 /tmp/record_mic.wav

Parameter description:

• -D hw:0,0: use PCM device 0 of sound card 0 (rockchip-es8389)

• -f S16_LE: 16-bit little-endian PCM format

• -r 48000: sample rate 48 kHz

• -c 2: two channels (stereo)

• -d 5: record for 5 seconds

To stop recording: recording stops automatically when the duration specified by -d is reached; you can also interrupt it by pressing Ctrl+C.

Headset Microphone Recording

After a headset is plugged in, the system automatically switches the recording input source to the headset microphone through headset detection (the headset MIC becomes the default recording input source at this time); after the headset is unplugged, it automatically switches back to the onboard MIC. You can also specify it manually:

arecord -D hw:0,0 -f S16_LE -r 48000 -c 2 -d 5 /tmp/record_headset.wav

Audio Playback

Speaker Playback

The default audio output of the M2 development board is the onboard speaker (through the PA amplifier). Play with aplay:

Headset/speaker auto-switching mechanism: The speaker and the headset of the M2 development board share the same DAC audio source (both are connected to HPOL/HPOR in the device tree audio-routing); the only difference is whether the PA amplifier on the output path is enabled. The system detects the headset insertion state in real time via hp-det-gpio + SARADC:

• Headset plugged in: once a headset is detected, the system automatically switches the default playback path to the headset (Headphone path) and disables the speaker PA (spk-con-gpio driven low, Speaker DAPM powered off). Sound is output from the headset only; the recording input switches to the headset microphone at the same time.

• Headset unplugged: once headset removal is detected, the system automatically switches back to the onboard speaker (Speaker path) and re-enables the PA (spk-con-gpio driven high). Sound is output from the speaker; the recording input switches back to the onboard MIC.

Therefore, the speaker and the headset play the same audio data; no separate source configuration is needed, and only the hardware output path (PA enable) differs.

aplay -D hw:0,0 /tmp/test.wav

Headset Playback

After a headset is plugged in, the system automatically routes audio to the headset. You can also specify the playback device manually:

aplay -D hw:0,0 /tmp/test.wav

HDMI Audio Playback

HDMI audio uses an independent sound card (rockchip-hdmi); use sound card 2:

aplay -D hw:2,0 /tmp/test.wav

Volume Control

Viewing the Current Volume

amixer -c 0 sget 'DACL'
amixer -c 0 sget 'DACR'

Setting the Volume

# Set the left-channel DAC volume to -6 dB (179)
amixer -c 0 cset numid=51 179

# Set the right-channel DAC volume to -6 dB (179)
amixer -c 0 cset numid=52 179

# Or set it by control name (0 dB = 191, -6 dB = 179, 0.5 dB per step)
amixer -c 0 sset 'DACL' 179
amixer -c 0 sset 'DACR' 179

The volume value maps to dB as: dB = -95.5 + 0.5 × value, i.e.:

• 191 → 0 dB

• 179 → -6 dB

• 167 → -12 dB

• 143 → -24 dB

Setting the Microphone Gain

# Set the left-channel MIC PGA gain (0~14, 3 dB per step)
amixer -c 0 sset 'ADCL PGA' 8

# Set the right-channel MIC PGA gain
amixer -c 0 sset 'ADCR PGA' 8

Viewing Complete Information of All ALSA Controls

amixer -c 0 contents

PipeWire / PulseAudio Architecture

Overview

The Debian system on the M2 development board uses PipeWire + WirePlumber as the audio service framework and provides a PulseAudio compatibility layer (pipewire-pulse). All PulseAudio commands such as pactl/paplay/parec can therefore be used directly. WirePlumber is responsible for the automatic management of audio devices and routing.

Device Inspection and Management

1. View available output devices (sinks)

pactl list short sinks

Typical output on the M2 development board:

0	alsa_output.platform-es8389-sound.analog-stereo	PipeWire	s32le 2ch 48000Hz	SUSPENDED
1	alsa_output.platform-hdmi-sound.hdmi-stereo		PipeWire	s32le 2ch 48000Hz	SUSPENDED

• alsa_output.platform-es8389-sound.analog-stereo: onboard audio (speaker/headset)

• alsa_output.platform-hdmi-sound.hdmi-stereo: HDMI audio

• A bluez_output.xxx sink appears dynamically after a Bluetooth speaker/headset is connected

Note: Accessing via adb logs in as root by default; you need to switch to a normal user. Example:

root@linaro-alip:/# pactl list short sinks
Connection failure: Connection refused
pa_context_connect() failed: Connection refused
root@linaro-alip:/# su w
w@linaro-alip:/$ pactl list short sinks
56      alsa_output.platform-es8389-sound.analog-stereo PipeWire        s32le 2ch 48000Hz       SUSPENDED

2. View input devices (sources)

pactl list short sources

Typical input on the M2 development board:

0	alsa_input.platform-es8389-sound.analog-stereo	PipeWire	s32le 2ch 48000Hz	SUSPENDED

A bluez_input.xxx source appears dynamically after a Bluetooth headset (HFP) is connected.

3. View detailed device information

pactl list sinks
pactl list sources

Setting the Default Output/Input Device

# Set the default output to the onboard speaker/headset
pactl set-default-sink alsa_output.platform-es8389-sound.analog-stereo

# Set the default output to HDMI
pactl set-default-sink alsa_output.platform-hdmi-sound.hdmi-stereo

# Set the default input to the onboard MIC
pactl set-default-source alsa_input.platform-es8389-sound.analog-stereo

Recording

Onboard MIC Recording

pactl set-default-source alsa_input.platform-es8389-sound.analog-stereo
parec --file-format=wav /tmp/output_mic.wav

To stop recording, press Ctrl+C.

Headset MIC Recording

After a headset is plugged in, WirePlumber automatically switches the default input route to the headset microphone (the headset MIC becomes the default recording input source at this time); after the headset is unplugged, it automatically switches back to the onboard MIC. You can also specify it manually:

parec --file-format=wav /tmp/output_headset.wav

Playback

Speaker/Headset Playback

paplay /tmp/test.wav

Output goes to the onboard audio by default. The speaker and the headset share the same DAC audio source; the system switches automatically through headset detection: plugging in a headset switches to the headset automatically (speaker PA disabled), and unplugging it switches back to the speaker (PA re-enabled). No manual configuration is required.

Playing to a Specific Sink

# Play to the onboard speaker/headset
paplay --device=alsa_output.platform-es8389-sound.analog-stereo /tmp/test.wav

# Play to HDMI
paplay --device=alsa_output.platform-hdmi-sound.hdmi-stereo /tmp/test.wav

Volume Control

Viewing/Setting the Output Volume

# View the volume of all sinks
pactl list sinks | grep -E 'Sink|Volume|Mute'

# Set the volume (percentage)
pactl set-sink-volume @DEFAULT_SINK@ 80%

# Mute/unmute
pactl set-sink-mute @DEFAULT_SINK@ toggle

Viewing/Setting the Input Volume

# Set the microphone volume
pactl set-source-volume @DEFAULT_SOURCE@ 80%

# Mute the microphone
pactl set-source-mute @DEFAULT_SOURCE@ toggle

GNOME Desktop Usage Guide

The Debian system on the M2 development board ships with the GNOME desktop (Wayland) by default. Audio settings are integrated into the system settings.

Opening Sound Settings

Click the volume icon in the top-right status bar → select “Sound Settings”; or open the “Settings” app → select “Sound”.

Screencast From 2026-04-14 04-56-13

Switching the Output Device

In “Settings → Sound → Output”:

1. Device: select the output device (onboard audio / HDMI / Bluetooth speaker)

2. Volume: drag the slider to adjust the output volume

3. Mute: click the speaker icon to mute/unmute

4. Bluetooth devices: connected Bluetooth speakers/headsets appear in the device list automatically

Tip: The onboard audio output (speaker/headset) shares the same DAC audio source. When a headset is plugged in, the system automatically switches the output to the headset and disables the speaker PA; when it is unplugged, the output switches back to the speaker. In the GNOME sound settings you can see the output device switch among onboard audio/HDMI/Bluetooth.

Switching the Input Device

In “Settings → Sound → Input”:

1. Device: select the input device (onboard MIC / headset MIC / Bluetooth headset)

2. Volume: drag the slider to adjust the input (microphone) volume

3. Test: click the microphone icon to run a recording test

Quick Volume Control

• Shortcut keys: the volume up/down keys and the mute key on the keyboard control the volume directly

• Top status bar: click the volume icon and drag the slider

• Quick menu in the tray: click the drop-down arrow next to the volume icon to switch the output device directly

Bluetooth Audio

Overview

The M2 development board supports Bluetooth audio. The Bluetooth protocol stack uses BlueZ + PipeWire (libspa-0.2-bluetooth) and supports:

• A2DP: playback of high-quality stereo music on Bluetooth speakers/headsets

• HFP: hands-free calls on Bluetooth headsets (including the microphone)

• AVRCP: Bluetooth remote control (play/pause/previous/next)

Bluetooth audio is handled directly by the BlueZ plugin of PipeWire and does not need to pass through the ALSA sound card. The bt-sound (SAI2 SCO) sound card in the device tree is disabled in the WirePlumber configuration (/etc/wireplumber/wireplumber.conf.d/51-quectel-pi-m2-audio.conf); audio uniformly uses A2DP/HFP.

Connecting a Bluetooth Device

Method 1 (GNOME GUI):

1. Click the top-right status bar → the Bluetooth icon (or “Settings → Bluetooth”)

2. Turn on the Bluetooth switch

3. Click “Add Device” to search for Bluetooth speakers/headsets

4. Select the device to complete pairing

Method 2 (bluetoothctl command line):

# Enter the Bluetooth console
bluetoothctl

# Power on Bluetooth
power on

# Scan for devices
scan on

# Pair and connect (replace with the actual MAC address)
pair AA:BB:CC:DD:EE:FF
trust AA:BB:CC:DD:EE:FF
connect AA:BB:CC:DD:EE:FF

Playing Bluetooth Audio

After a successful connection, the Bluetooth speaker/headset automatically becomes the default output device; play directly:

paplay /tmp/test.wav

You can also specify the Bluetooth sink manually:

# View the Bluetooth sink name
pactl list short sinks

# Play to the Bluetooth device
paplay --device=bluez_output.AA_BB_CC_DD_EE_FF.1 /tmp/test.wav

Bluetooth Headset Microphone

The microphone of a Bluetooth headset (HFP mode) is automatically registered as an input source (bluez_input.xxx) and can be used for calls or recording:

# View the Bluetooth input sources
pactl list short sources

# Set the Bluetooth headset microphone as the default input
pactl set-default-source bluez_input.AA_BB_CC_DD_EE_FF.1

Note: The M2 development board has a built-in Bluetooth microphone gain optimization script (/usr/share/wireplumber/scripts/quectel/bluetooth-mic-gain.lua). When a Bluetooth headset is connected, the microphone gain is automatically set to 150% to ensure clear call/recording audio.

Troubleshooting

Problem	Possible Cause
No recording file generated	Check whether the recording command is correct. Check whether the working directory is readable/writable.
Audio playback fails	Check whether the audio file to play exists. Check whether the playback command is correct.
No sound from the speaker	Check whether the speaker is properly connected and the PA amplifier works. Check whether the DAC volume is muted (amixer -c 0 sget 'DACL Playback Volume'). Check whether the default sink has been switched to another device.
No sound from the headset	Check whether the headset is fully plugged in and headset detection is triggered. Check the default sink (pactl list short sinks).
Audio still comes from the speaker after plugging in the headset	Check whether headset detection (hp-det) is effective. Check whether WirePlumber is running (systemctl --user status wireplumber).
No sound over HDMI	Check whether HDMI is connected and the display supports audio return. Check whether the default sink is switched to HDMI (pactl set-default-sink alsa_output.platform-hdmi-sound.hdmi-stereo).
Cannot connect to Bluetooth	Check whether Bluetooth is enabled (bluetoothctl power on). Check whether the device is in discoverable mode. Check whether the PipeWire Bluetooth plugin is installed (libspa-0.2-bluetooth).
Bluetooth audio works but the microphone is silent	Confirm that the headset supports the HFP hands-free profile. Check whether the default source is switched to bluez_input.xxx.

List of Abbreviations

The abbreviations used in this document are explained below:

Audio Hardware and Technologies

Abbreviation	Full Name	Description
DACL / DACR	DAC Left / DAC Right	Independent DAC volume control channels for the left/right channels of the ES8389
PGA	Programmable Gain Amplifier	Gain amplifier on the microphone input channel; used to adjust the recording sensitivity (0~14, 3 dB per step)
DAPM	Dynamic Audio Power Management	Power management mechanism of the Linux ASoC subsystem; automatically switches power rails/PA on and off according to audio path usage
HPOL / HPOR	Headphone Output Left / Right	Headphone output pins of the ES8389; the audio source shared by the speaker and the headset
DMIC	Digital Microphone	Microphone that outputs digital signals directly (the onboard MEMS silicon microphone of the M2)
SAI	Serial Audio Interface	Audio interface controller of Rockchip processors (SAI1 connects to the ES8389, SAI6 to HDMI, SAI2 to the Bluetooth SCO)
SCO	Synchronous Connection-Oriented	Synchronous connection-oriented link for Bluetooth voice calls; used for HFP hands-free calls
SARADC	Successive Approximation Register ADC	Used for headset insertion detection (reads the headset-detect pin voltage to determine the plug/unplug state)

Bluetooth Protocols

Abbreviation	Full Name	Description
A2DP	Advanced Audio Distribution Profile	Transmits high-quality stereo music over Bluetooth (Bluetooth speaker/headset playback)
HFP	Hands-Free Profile	Hands-free calls on Bluetooth headsets; supports microphone input (voice calls/recording)
AVRCP	Audio/Video Remote Control Profile	Bluetooth remote control operations (play/pause/previous/next)
BLE	Bluetooth Low Energy	Low-power Bluetooth communication for low-rate data transfer and device connection
BlueZ	BlueZ Bluetooth Stack	The official Linux Bluetooth stack; works with PipeWire for Bluetooth audio

System and Software

Abbreviation	Full Name	Description
PipeWire	PipeWire	Next-generation Linux audio/video service framework; manages audio devices and routing (default audio service on the M2)
WirePlumber	WirePlumber	Session and policy manager of PipeWire; responsible for device discovery, routing and volume policy
pactl	PulseAudio Control	Command-line tool to view/control audio devices (sink/source, volume, routing)
sink	Sink	Audio output device (speaker/headset/HDMI/Bluetooth speaker)
source	Source	Audio input device (onboard MIC/headset MIC/Bluetooth headset)

Resources and Support

• ALSA Project

• PipeWire Documentation

• WirePlumber Documentation