Using BlueALSA as BLE MIDI server

Introduction

It is possible to use BlueALSA as a BLE-MIDI server. For that, the bluez-alsa project must be configured with the --enable-midi option. This will enable ALSA sequencer integration within the BlueALSA system service.

Running BlueALSA as a BLE-MIDI server

To run BlueALSA as a BLE-MIDI server, the bluealsa service must be started with Bluetooth LE MIDI profile enabled. Optionally, one can also enable Bluetooth LE advertisement for the MIDI service. Otherwise, LE advertisement has to be configured externally, e.g. with bluetoothctl. The disadvantage of using the built-in LE advertisement is that it is not possible turn it off without restarting the BlueALSA service (which will also disconnect BLE-MIDI clients).

bluealsa -p midi --midi-advertisement

This will create software MIDI input/output port which can be used as any other ALSA MIDI port. The MIDI port will be named BLE MIDI Server.

$ aseqdump -l
 Port    Client name        Port name
  0:0    System             Timer
  0:1    System             Announce
128:0    BlueALSA           BLE MIDI Server

Connecting to the BLE-MIDI server

Once the BlueALSA service is running, the BLE-MIDI client can connect to the server. However, in order to connect to the BLE-MIDI profile, the client must be paired with the server. By default, pairing process requires PIN code authentication. So, before connecting to the BLE-MIDI server, one has to run PIN code authentication application, or simply start bluetoothctl and wait for the pairing request.

Exemplary use cases

Using BLE-MIDI server with MIDI keyboard

Connect MIDI keyboard to the host and connect its MIDI output to the BLE MIDI Server port. With such configuration, the MIDI keyboard will be able to send MIDI messages to connected BLE-MIDI client.

1. Connect the MIDI keyboard to the host.

2. Connect the MIDI keyboard output to the BLE MIDI Server port.

   aconnect <MIDI keyboard> <BLE MIDI Server>

   E.g.:

   pi@rpi:~ $ aconnect -l
   client 24: 'Digital Piano' [type=kernel,card=2]
       0 'Digital Piano MIDI 1'
   client 128: 'BlueALSA' [type=user,pid=314]
       0 'BLE MIDI Server '
   
   pi@rpi:~ $ aconnect 24:0 128:0
   
   pi@rpi:~ $ aconnect -l
   client 24: 'Digital Piano' [type=kernel,card=2]
       0 'Digital Piano MIDI 1'
           Connecting To: 128:0
   client 128: 'BlueALSA' [type=user,pid=314]
       0 'BLE MIDI Server '
           Connected From: 24:0

Using BLE-MIDI server with MIDI software synthesizer

Install software synthesizer, e.g. timidity, and run it as a service. Then connect BLE MIDI Server port with the synthesizer input port.

1. Install timidity system service.

   sudo apt install timidity-daemon

2. Connect the BLE MIDI Server port with the timidity input port.

   pi@rpi:~ $ aconnect -l
   client 128: 'BlueALSA' [type=user,pid=314]
       0 'BLE MIDI Server '
   client 129: 'TiMidity' [type=user,pid=315]
       0 'TiMidity port 0 '
       1 'TiMidity port 1 '
       2 'TiMidity port 2 '
       3 'TiMidity port 3 '
   
   pi@rpi:~ $ aconnect 128:0 129:0
   
   pi@rpi:~ $ aconnect -l
   client 128: 'BlueALSA' [type=user,pid=314]
       0 'BLE MIDI Server '
           Connecting To: 129:0
   client 129: 'TiMidity' [type=user,pid=315]
       0 'TiMidity port 0 '
           Connected From: 128:0
       1 'TiMidity port 1 '
       2 'TiMidity port 2 '
       3 'TiMidity port 3 '