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Francois Corthay edited this page Sep 25, 2026 · 12 revisions

The BlueTooth (BT) protocol allows to change your Raspberry Pi (RPi) into an audio receiver.

Table of Contents

Audio path

The audio path considered here is the one of a multiroom streamer which also acts as a local player:

The digital signal processing (DSP) is not mandatory: the snapclient can stream directly to the audio (amplifier) output.

In the case of a simple multiroom audio receiver, the mopidy sound source and the snapserver audio streamer are absent. In this case, the Bluetooth reciever has to be multiplexed to the snapclient output.

Setup

User

Give the user access to BT: 

USER='amp'
sudo usermod -a -G bluetooth $USER
cat /etc/group | grep ^bluetooth

Bluetooth

First of all, one has to unblock the service: 

rfkill list
sudo rfkill unblock bluetooth
rfkill list

In order to serve as a BT audio receiver, edit the BT configuration: 

sudo nano /etc/bluetooth/main.conf

and change:

  • Class = 0x404
  • DiscoverableTimeout = 0
  • PairableTimeout = 0
  • AlwaysPairable = true
One can also set the device's name in the same configuration file: 
Name = BluePi

Restart the service: 

sudo systemctl restart bluetooth

ALSA backend

On a desktop system, pipewire redirects Bluetooth audio to the speakers. If one want to go through ALSA, one has to disable it: 

systemctl --user disable --now pipewire.service pipewire-pulse.service wireplumber.service
systemctl --user mask pipewire.service pipewire-pulse.service wireplumber.service

Install the BT audio ALSA backend: 

sudo apt install -y bluez-alsa-utils bluez-tools
#sudo service bluealsa start

From these, bluealsa serves the Advanced Audio Distribution Profile (A2DP) pairing. It generates an audio source called bluealsa as seen from the command: 

aplay -L | head -n 20

As we only want to sink audio, the service configuration has to be changed: 

sudo nano /lib/systemd/system/bluealsa.service

Change the command to: 

#ExecStart=/usr/bin/bluealsa -S -p a2dp-source -p a2dp-sink
ExecStart=/usr/bin/bluealsa -p a2dp-sink

Restart the service: 

sudo systemctl daemon-reload
sudo service bluealsa restart

As we are going to use the play command differently, disable the bluealsa-aplay service : 

sudo systemctl disable bluealsa-aplay
sudo systemctl daemon-reload

BT connection

Clear BT history: 

sudo systemctl stop bluetooth
sudo rm -rf /var/lib/bluetooth/*
sudo systemctl start bluetooth

Clear list of connected devices: 

bluetoothctl devices | awk '{print $2}' | while read dev; do bluetoothctl remove $dev; done

Prepare RPi for connection: 

bluetoothctl power on
bluetoothctl discoverable on
bluetoothctl pairable on

Pair a device to the RPi: 

/bin/sh -c 'yes | /usr/bin/bt-agent -c NoInputNoOutput'

Save your connection: 

PLAYER=`bluetoothctl player.list | sed 's/.*dev_//' | sed 's/\/.*//' | sed 's/_/:/g'`
echo "saving connection from $PLAYER"
bluetoothctl trust $PLAYER

Check the status: 

bluetoothctl show

BT connected devices

Check for BT connected devices: 

bluetoothctl player.list

List the processes linked to BT: 

busctl | head -n 1 | cut -c -$COLUMNS ; busctl | grep -i blue | cut -c -$COLUMNS

First tests

Audio path

Beware: the RPi uses the same radio chip for Ethernet and Bluetooth. If your BT audio stutters, do consider to connect your RPi to a wired Ethernet connection.

Check the audio path: 

$AUDIO_BASE_DIR/Management/showInstallation.bash

The BT audio source bluealsa samples 16 bit audio at a 44.1 lHz sampling rate. This has to be encoded and resampled to the sample bit number and the sampling rate of the audio chain.

If playing, pause Mopidy: 

$AUDIO_BASE_DIR/Mopidy/control.bash pause

Connect a smartphone or any other Bluetooth audio source device to the RPi and start playing.

On the RPi, send the audio to the same sink as Mopidy, e.g.: 

bluealsa-aplay -D plug:dmix:Loopback,0,1 --pcm-buffer-time=5000000

I had a RPi that rejected the device plug:dmix:Loopback,0,1. The workaround has been: 

ALSA_CONFIG_PATH=<(cat /usr/share/alsa/alsa.conf; echo 'pcm.plugdmix01 { type plug slave.pcm "dmix:Loopback,0,1" }') \
bluealsa-aplay -D plugdmix01 --pcm-buffer-time=5000000

Adjust the buffer time (given in microseconds) to have flawless music playing.

Source switching

Both mopidy and bluealsa-aplay stream their audio to the same sink. So in order to hear only one of them, one has to pause the other: 

$AUDIO_BASE_DIR/Mopidy/control.bash -v pause
$AUDIO_BASE_DIR/Bluetooth/control.bash -v play
# or
$AUDIO_BASE_DIR/Bluetooth/control.bash -v pause
$AUDIO_BASE_DIR/Mopidy/control.bash -v play

The control script: 

$AUDIO_BASE_DIR/Bluetooth/streamControl.bash -v

runs an infinite loop which:

  • on the connection of a Bluetooth device
    • pauses mopidy
    • sends a play command to the Bluetooth device
  • on the disconnection of the Bluetooth device
    • sends a play command to mopidy

Service

In order to have automatic BT streaming when a device is connected, a service is used. Edit the service definition file to adjust the parameters: 

nano $AUDIO_BASE_DIR/Bluetooth/dac-bluetooth.service

Then setup the service: 

sudo cp $AUDIO_BASE_DIR/Bluetooth/dac-bluetooth.service /lib/systemd/system/
sudo systemctl daemon-reload
sudo systemctl enable --now dac-bluetooth.service

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