LooperTRX

This tool allows transferring recorded audio data from/to some China-made looper pedals (see also: https://en.wikipedia.org/wiki/Looper_pedal) over USB. Unfortunately they are officially only supported by a Windows tool. To be able to use them with Linux, I analyzed and replicated their USB protocol in this small script. Though I only tested it with Linux, it should work on all platforms supported by pyusb (e.g. MacOSX, *BSD).

I primarily wrote the tool to get support for my "Harley Benton Mini Looper", but I found that several other brands use the same OEM product; even the transfer software binaries are almost identical (with minor differences because of varying company logos).

The compatible loopers that I found so far are:

• Harley Benton Mini Looper
• FAME Looper
• Rowin LEF-332
• Donner Looper
• ammoon AP-09 nano looper

Note: The Harley Benton looper has the USB ID 0483:572a, so the software is looking for these devices. Please let me know if other devices are using different IDs.

Usage

Call it without any parameters to start the graphical interface (if tkinter is available).

For command line usage:

$ loopertrx.py rx audio.wav Receiving..... Done.

$ loopertrx.py tx audio.wav Transmitting..... Done.

Data format

The looper stores files as mono PCM WAV files with 24 bits per sample and a sample rate of 48000 Hz. To convert arbitrary audio files to this format, the swiss army knife of sound processing (sox) can be used:

$ sox input.mp3 -c1 -r 48000 -b 24 -t wavpcm output.wav

External dependencies

• pyusb (https://walac.github.io/pyusb/) (On Debian systems: # apt install python3-usb)
• tkinter [optional] (installed by default on most systems) (On Debian systems: # apt install python3-tk)

Linux notes

To allow unprivileged users access to the devices, a udev rule can be created. Create the file /etc/udev/rules.d/99-looperpedal.rules with the following content:

SUBSYSTEM=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="572a", GROUP="plugdev", MODE="0660"

Users in the 'plugdev' group will then be allowed to send/receive data.

Current limitations

The official Windows transfer tool does additional audio processing of the received/sent data (what they store is not the same data that is transferred over USB). The files are slightly larger in size, perhaps because of some speed adjustments for local playback. LooperTRX curently only stores/restores the raw data from the looper devices, without any modifications. Because of this the audio sounds slightly different when played back on a computer.