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Configure Audio

Patchbox OS Setup Wizard

This fork assumes you're running Blokas Patchbox OS. Therefore, you need to configure the default sound card using the Setup Wizard. You can launch the Setup Wizard at any time by typing patchbox in Terminal.

USB Audio Card

  • f you're using a Raspberry Pi 4 Model B with 1Gb RAM or higher and a USB sound card with this chip or anything better you should be able to run with a Sampling Rate of 48,000 Hz, a Buffer Size of 64 and a Period between 3 and 4.

Pisound

  • If you're using a Raspberry Pi 4 Model B with 4Gb RAM or higher and a Pisound, I recommend using a Sampling Rate of 48,000 Hz, a Buffer Size of 64 and a Period of 4.

Notes About Latency

  • Based on my experiments, a setup consisting of M8 (using audio in/out) and MC-101 (connected via USB, either in Vendor or Generic Driver Mode) will perform consistently well and without undesired audio artifacts using a Sampling Rate of 44,100 Hz, a Buffer Size of 64 and a Period of 4. This configuration should give you about 6 ms of nominal latency according to this link.

  • This latency should not be a problem unless you want to play the instruments with a keyboard or if you connect this setup to additional gear. Both the M8 and the MC-101 have the same latency, therefore you generally won't notice it until you connect something to the audio input.

USB Connections

If your USB sound card and/or your additional USB Class Compliant instrument(s) support USB 3.0, then you should connect them to the blue USB ports of your Raspberry Pi 4. This may help reduce audio latency and improve the overall performance of the setup.

The Teensy 4.1 only supports USB 2.0 (480 Mbit/sec). Therefore, it can be connected to the black USB ports of your Raspberry Pi 4.

M8C Bash Script

After configuring the default sound card using the Setup Wizard, you will need to configure this script according to your preferences. This script is responsible for connecting the audio in/out of the M8 and/or other connected instruments to the default sound card selected in the Setup Wizard.

Important: You should not start the JACK server using jackd -d alsa -d hw:M8 -r44100 -p512 & (or a similar configuration) because this service is automatically started upon boot by Patchbox OS. You will see errors if you attempt to do this.

M8 Headless

For optimal performance and to avoid resampling, the alsa_in / alsa_out options of the connected devices should match those selected in the Setup Wizard. So, for example, if you selected a Sampling Rate of 44,100 Hz, a Buffer Size of 64 and a Period of 4 in the Setup Wizard, then the alsa_in / alsa_out should look like this for M8:

alsa_in -j "M8_in" -d hw:M8,DEV=0 -r 44100 -p 64 -n 4 &
alsa_out -j "M8_out" -d hw:M8,DEV=0 -r 44100 -p 64 -n 4 &

However, the Pisound does not support 44,100 Hz. Therefore, you'll have to use 48,000 Hz for the Pisound. Unfortunately, the Teensy only supports 44,100 Hz. This means there will be some resampling between the Pisound and the Teensy, which will use some resources. I did not find any issues with this in a Raspberry Pi 4 Model B with 4Gb RAM.

Roland MC-101

The alsa_in / alsa_out section should look like this for the MC-101 in Generic Driver Mode or any other USB Class Compliant instrument you plan to connect (don't forget to change the device name MC101 if you're using a different device):

alsa_in -j "MC101_in" -d hw:CARD=MC101,DEV=0 -r 44100 -p 64 -n 4 &
alsa_out -j "MC101_out" -d hw:CARD=MC101,DEV=0 -r 44100 -p 64 -n 4 &

If you're using the MC-101 in Vendor Driver Mode (which in my opinion, works much better than Generic Dirver Mode), then the alsa_in / alsa_out section should look like this:

alsa_in -j "MC101_in" -d hw:MC101,DEV=0 -r 44100 -p 64 -n 4 -c 10 &
alsa_out -j "MC101_out" -d hw:MC101,DEV=0 -r 44100 -p 64 -n 4 -c 4 &

This creates ports for 10 Channels Out (1+2 Master Out; 3+4 Track 1; 5+6 Track 2; 7+8 Track 3; 9+10 Track 4) and ports for 4 Channels In (1+2 Master In, which bypasses controls; 3+4 PC In, which allows controls).

Other Options

If, instead of connecting a MC-101 to your setup, you're planning to connect a different USB Class Compliant instrument, then you need to replace all the instances of MC101 in this script with the Card Name of your instrument.

Alternatively, if you're not connecting any additional device to your setup besides the M8, then you can completely remove the following section from this script:

# Check if the Instrument with the Card Name "MC101" is connected to the Raspberry Pi
(...)
fi

Instead of using alsa_in / alsa_out, you can use jack_load to create the ports for all in and out channels. To create all the in and out ports for the MC-101 in generic mode, enter the following (The -o and -i options refer to the number of outout and input channels, respectively):

jack_load -i "-d hw:MC101,DEV=0 -r 44100 -p 64 -n 4 -o 2 -i 2" MC101 audioadapter &

Important Commands

To find the Card Name of your instrument, connect it to the Raspberry Pi and type aplay -l.

You can also use cat /proc/asound/cards to list all the audio devices and find their names or aplay --list-devices to list all playback devices and arecord --list-devices to list all the recording devices.

After creating the ports with either alsa_in / alsa_out or jack_load, you'll need to connect them using jack_connect portname1 portname2.

You can then check the connections using jack_lsp -c.

To disconnect ports you can use jack_disconnect portname1 portname2. To remove the created ports (after disconecting them), use killall -s SIGINT alsa_in alsa_out if you're using alsa_in / alsa_out or jack_load portname if you're using jack_load.

Alsamixer Levels and Noise Suppression

Depending on the type and/or model of audio card you are using for this project, you may need to adjust the audio input and output levels.

To do that, open a terminal and type alsamixer. Then, using the arrows, adjust the output and input levels of your audio card.

While in alsamixer, you should also check for any undesired noises coming from the USB sound card or any other devices. You can play with the levels to suppress the noise and/or disable Auto Gain Control to hear how it impacts the noise.

As an example, I'm using the following audio configuration and levels:

Card M8: PCM Mute
Card USB Audio Device: Speaker 54<>54 (dB gain: -16); Mic Mute or 0; Capture 53 (dB gain: 12); Auto Gain Control Mute or Off

Exit alsamixer using escape and save your adjustments by typing sudo alsactl store.

References

For more information, please visit JACK Audio Connection Kit wiki. This link is also very helpful.