Audio Through USB

Using USB Audio Gadget

NOTE: For best results please use v1.14 or later

NOTE: This is EXPERIMENTAL

First ssh into the unit, and run:

touch /data/enable-usb-multi-gadget
touch /data/enable-usb-audio-gadget
# if using windows, also run:
touch /data/enable-usb-windows-compat

Now we reboot

sync && hmi-reset && reboot

Some caveats and known issues:

• Only 48000 Hz sample rate is supported (this is intentional, matches the internal sample rate of the unit)
• USB audio requires very precise timings, loading big resources on the web interface over USB can lead to audio dropouts (best results are achieved with web interface over WiFi, leaving USB for audio and MIDI)
• MOD Duo X "limited edition" only works in capture mode
• For use in Windows, an up-to-date Windows 10 or later is required

Forum Threads:

• https://forum.moddevices.com/t/duo-x-as-usb-audio-input-and-midi-device-experimental/3469
• https://forum.moddevices.com/t/solved-usb-audio-jack-with-pipewire-on-linux-how-to-mod-duo/7723/7

Windows specific tweaks

When picking an audio driver/mode look for "WASAPI" or "Windows Audio".
If there is an option for "exclusive mode" try that first; it won't allow other applications to use the usb audio device at the same time but it reduces the amount of latency.

Under this WASAPI/Windows-Audio mode with 512 buffer size we have measure roundtrip latencies of around 80ms in normal/shared mode, and 65ms in exclusive mode.
Latency decreases if you use the MOD unit analog IO.

ASIO4ALL

Using ASIO4ALL has been confirmed to work, but needs some tweaks:

• Set buffer size to 128 or higher
• In advanced settings set buffer offset to 16ms
• Turn off all other options in advanced settings

This should result in around 60ms total roundtrip latency, will be less if you use the MOD unit analog IO.

FL Studio ASIO

The FL Studio ASIO driver has also been confirmed to work, no special tweaks needed.
Its minimum buffer size of 256 should work fine as-is.

In our measurements it gives a total roundtrip latency of around 75ms, will be less if you use the MOD unit analog IO.

Using netJACK2

NOTE: This requires the use of JACK as sound server in your PC.

First, connect the MOD unit to your PC via usb cable. Make sure to open port 19000 on your firewall. If you use Linux with ufw, you can use:

sudo ufw allow 19000

Then, ssh into the unit, and run:

touch /data/enable-netmanager
systemctl start jack-netmanager

NOTE: You only need to run this command once. The next time the unit boots, jack-netmanager will be loaded by default. Delete the /data/enable-netmanager file inside the unit to remove this auto-start feature.

Now run jackd on your own computer (connected to the unit via USB), like this:

jackd -R -P 80 -d net -a 192.168.51.1 -C 2 -P 2 -i 1 -o 1 -l 4 -n mod-slave -s

Adjust the parameters as needed, but keep mod-slave as the client name.

Parameters explained

-R	Use realtime scheduling, enabled by default.
-P	Set the realtime scheduling priority, in this case 80.
-d	JACK backend, in this case the "net" driver.
-a	Multicast address, in this case the IP address of the MOD unit.
-C	Number of audio input ports on the slave. This determines the number of audio output ports on the MOD unit, marked as "Hardware Audio To Slave" ports in the web interface.
-P	Number of audio output ports on the slave. This determines the number of audio input ports on the MOD unit, marked as "Hardware Audio From Slave" ports in the web interface.
-i	Number of MIDI input ports on the slave. This determines the number of MIDI output ports on the MOD unit, marked as "Hardware Midi To Slave" ports in the web interface.
-o	Number of MIDI output ports on the slave. This determines the number of MIDI input ports on the MOD unit, marked as "Hardware Midi From Slave" ports in the web interface.
-l	Number of cycles, determines the network latency.
-s	Setting this option makes the JACK slave memorize the ports that are connected to the JACK master. In case the master disappears and reappears the JACK slave will try to reconnect those ports automatically.

or if you prefer to use jackdbus:

jack_control eps realtime true eps realtime-priority 80
jack_control ds net dps multicast-ip 192.168.51.1 dps client-name mod-slave
jack_control dps input-ports 2
jack_control dps output-ports 2
jack_control dps midi-in-ports 1
jack_control dps midi-out-ports 1
jack_control dps latency 4
jack_control dps auto-save true
jack_control start