Tutorial for Virtual Audio Input/Loopback

[TobKra96]

Create a Tutorial for a virtual audio input device or a loopback config.
Maybe we can use a Spotify connect app like https://github.com/dtcooper/raspotify

[spiro-c]

I have done this whit pulseaudio server and spotifyd but you can use any audio source like vlc ... what is playing on the pi

then using the pulsemixer MLSC can be hook to source you like to get audio from

i have use the same method whit the LedFX project but and here is working

[TobKra96]

Wow, this is really cool. Thank you. I will install it on my system and write a small tutorial 👍

[TobKra96]

My first test failed. It seems like portaudio and pulseaudio fight against each other 😄.
Pyaudio returned this:

ALSA lib pulse.c:243:(pulse_connect) PulseAudio: Unable to connect: Connection refused

I have already tried to uninstall Portaudio, but PyAudio stopped working after this. 😕
Don't worry, I will go into the fight for the next round. 😄

Have a great day
TobKra

[spiro-c]

I have problem using this on the dev2.2 branch i never manage to get it running but on the master i dont have problem

[TobKra96]

Ok, thanks for the info. I will check it :)

[carlyd95]

I was able to get a loopback method working with Librespot (dependency of rasp-tidy) back in September of last year for my longboard before I broke the damn thing haha. (Here: Longboard Lights) And just recently I attempted a different method using BlueAlsa AD2P. I know the BlueAlsa AD2P one doesn't require PulseAudio or PortAudio, the Librespot might have worked with just ALSA too. (tested with RPi 4)

[TobKra96]

Nice, I will give it a try :)

[carlyd95]

I got my setup working well and wanted to share... :D

---

Purpose:

• Alleviate the need for a microphone
• Soley sample the streamed audio (not ambient noise)
• Output audio via USB soundcard

Audio Input Options:

• BlueALSA (Bluetooth A2DP) [confirmed]
• Librespot (Spotify speaker) [confirmed]
• Shairport Sync (Airplay speaker) [possibility]

---

Loopback Tutorial (BlueALSA version):

1. Install BlueALSA

• sudo apt install bluealsa

2. Enabling Audio Profile Sink Role
3. Open the configuration file for bluealsa service

• sudo nano /lib/systemd/system/bluealsa.service
• Change ExecStart=/usr/bin/bluealsa to ExecStart=/usr/bin/bluealsa -p a2dp-sink
• Save changes

4. Reboot

• sudo reboot

5. Start ALSA loop

• sudo modprobe snd-aloop
• (optional) set up a systemd service or add it in /etc/rc.local that runs this at boot

6. Configure asound.conf

• sudo nano /etc/asound.conf
• refer to attached asound.conf.txt file (it sets up a multi named both and plays to loopout for MLSC and hw:1,0, the USB soundcard)

7. Connect to A2DP

• sudo apt install expect
• run attached autobt.sh script file (don't forget file permissions)

OR

• or use bluetoothctl

8. Direct Audio Stream to "both" previously setup in asound.conf

• play audio on the device you used to connect to the RPi A2DP
• bluealsa-aplay -d both 00:00:00:00:00:00
• (optional) set up a systemd service that runs this at boot

9. Start MLSC If Not Running

• change audio input source to whichever corresponds to loopout (not loopin!)
• restart MLSC

DONE!

---

Notes:
I have experienced some issues with the sample rate. Example: PyAudio says loopout's sample rate is 44,100 but MLSC's music effects do not function properly with this sample rate, instead I have found a few random ones when input do. I am using 24000.

---

Sources Used:

• A2DP tutorial

---

Thanks for everyone's work on this project!

If anyone needs help trying this let me know, and if I made any mistakes or something isn't working just let me know :)

[JohnGuan]

I used this config from https://trac.ffmpeg.org/wiki/Capture/ALSA

Record audio from an application while also routing the audio to an output device

modprobe snd-aloop pcm_substreams=1

# /etc/asound.conf
pcm.multi {
    type route;
    slave.pcm {
        type multi;
        slaves.a.pcm "output";
        slaves.b.pcm "loopin";
        slaves.a.channels 2;
        slaves.b.channels 2;
        bindings.0.slave a;
        bindings.0.channel 0;
        bindings.1.slave a;
        bindings.1.channel 1;
        bindings.2.slave b;
        bindings.2.channel 0;
        bindings.3.slave b;
        bindings.3.channel 1;
    }

    ttable.0.0 1;
    ttable.1.1 1;
    ttable.0.2 1;
    ttable.1.3 1;
}

pcm.!default {
	type plug
	slave.pcm "multi"
} 

pcm.output {
	type hw
	card 0 # Your Output Device Name
}

pcm.loopin {
	type plug
	slave.pcm "hw:Loopback,0,0"
}

pcm.loopout {
	type plug
	slave.pcm "hw:Loopback,1,0"
}

The mpg123 and shairport-sync are worked.
But MLSC just not working, even it found a list of audio devices.
It drives me crazy, does anyone have work way?

[carlyd95]

I used this config from https://trac.ffmpeg.org/wiki/Capture/ALSA

Record audio from an application while also routing the audio to an output device

modprobe snd-aloop pcm_substreams=1

# /etc/asound.conf
pcm.multi {
   type route;
   slave.pcm {
       type multi;
       slaves.a.pcm "output";
       slaves.b.pcm "loopin";
       slaves.a.channels 2;
       slaves.b.channels 2;
       bindings.0.slave a;
       bindings.0.channel 0;
       bindings.1.slave a;
       bindings.1.channel 1;
       bindings.2.slave b;
       bindings.2.channel 0;
       bindings.3.slave b;
       bindings.3.channel 1;
   }

   ttable.0.0 1;
   ttable.1.1 1;
   ttable.0.2 1;
   ttable.1.3 1;
}

pcm.!default {
 type plug
 slave.pcm "multi"
} 

pcm.output {
 type hw
 card 0 # Your Output Device Name
}

pcm.loopin {
 type plug
 slave.pcm "hw:Loopback,0,0"
}

pcm.loopout {
 type plug
 slave.pcm "hw:Loopback,1,0"
}

The mpg123 and shairport-sync are worked.
But MLSC just not working, even it found a list of audio devices.
It drives me crazy, does anyone have work way?

Does it show the loopout or loopin as one of the sources and you are selecting that source for MLSC to use?

[JohnGuan]

I used this config from https://trac.ffmpeg.org/wiki/Capture/ALSA
Record audio from an application while also routing the audio to an output device

modprobe snd-aloop pcm_substreams=1

# /etc/asound.conf
pcm.multi {
   type route;
   slave.pcm {
       type multi;
       slaves.a.pcm "output";
       slaves.b.pcm "loopin";
       slaves.a.channels 2;
       slaves.b.channels 2;
       bindings.0.slave a;
       bindings.0.channel 0;
       bindings.1.slave a;
       bindings.1.channel 1;
       bindings.2.slave b;
       bindings.2.channel 0;
       bindings.3.slave b;
       bindings.3.channel 1;
   }

   ttable.0.0 1;
   ttable.1.1 1;
   ttable.0.2 1;
   ttable.1.3 1;
}

pcm.!default {
 type plug
 slave.pcm "multi"
} 

pcm.output {
 type hw
 card 0 # Your Output Device Name
}

pcm.loopin {
 type plug
 slave.pcm "hw:Loopback,0,0"
}

pcm.loopout {
 type plug
 slave.pcm "hw:Loopback,1,0"
}

The mpg123 and shairport-sync are worked.
But MLSC just not working, even it found a list of audio devices.
It drives me crazy, does anyone have work way?

Does it show the loopout or loopin as one of the sources and you are selecting that source for MLSC to use?

Ummm... yes.. I tried everyone

[carlyd95]

@JohnGuan

in my asound.conf I have my loop configured a lil different, worth a try:

pcm.loopin {
type plug
slave.pcm "plughw:Loopback,0,0"
}

pcm.loopout {
type plug
slave.pcm "plughw:Loopback,1,0"
}

[JohnGuan]

@carlyd95 Thank you for your generous answer.
In fact, I tried yours. It doesn't work.😂
I think I may need to re-flash the system. My current system is Raspberry Pi OS Lite.
I'm not quite sure if it has any effect, but the PulseAudio solution written in the previous reply seems to be more dependent on the desktop environment.

[carlyd95]

@JohnGuan weird, mine works just fine using BlueALSA as an A2DP 😆 I’ll have to mess with shairport sometime soon.