socradoc

The socradoc repository contains 3rd party documentation on the Soundcraft's Notepad series of analog mixers with USB audio and USB control of some functions.

The socradoc repository is NOT related to or affiliated with Soundcraft at all. If you are looking for Soundcraft themselves, this is the wrong place. Go visit the Soundcraft website instead.

doc/soundcraft-notepad-usb-protocol.md describes how to tell a Soundcraft Notepad series mixer device which audio channels to route to the USB capture device, and whether and how to configure the Ducker for the USB playback.

The scnp-cli utility is a simple CLI written in C which implements the USB control commands described in doc/soundcraft-notepad-usb-protocol.md to make help verify the protocol description is accurate.

The Soundcraft Notepad series consists of these three devices:

If you want a nice GUI for controlling a Notepad mixer but Soundcraft does not provide one for your computer, go over to soundcraft-utils for a nice GUI which even synchronizes between multiple instances of its GUI and CLI. soundcraft-utils is written in Python, uses a D-Bus service to provide a better user experience across tool invocations, and uses Gtk3 for the GUI.

scnp-cli could also be helpful if you do not want to install the whole Python software stack just to change the mixer's audio routing to the USB device.

Runtime requirements

Unless you have statically linked scnp-cli, you need a libc (glibc?) and libusb-1.0 for running scnp-cli.

Usage

This is the output of scnp-cli --help. A more detailed description is available in the scnp-cli(1) man page.

Usage: scnp-cli <command> <command_params...>

Gives command line access to the USB control commands for the Soundcraft
Notepad series of mixers to help verify the USB protocol description document.

Commands:

    --help     Print this usage message and exit.

    --version  Print version message and exit.

    audio-routing <NUM>
               Find a supported device, and set its audio sources.
               There must be exactly one supported device connected.
               The valid source numbers are specific to the device:

               NOTEPAD-5 channels 1+2 of 2-channel audio capture device
                 0  MIC+LINE 1+2
                 1  LINE 2+3
                 2  LINE 4+5
                 3  MASTER L+R

               NOTEPAD-8FX channels 1+2 of 2-channel audio capture device
                 0  MIC 1+2
                 1  LINE 3+4
                 2  LINE 5+6
                 3  MASTER L+R

               NOTEPAD-12FX channels 3+4 of 4-channel audio capture device
                 0  MIC 3+4
                 1  LINE 5+6
                 2  LINE 7+8
                 3  MASTER L+R

               Note that on the NOTEPAD-12FX 4-channel audio capture device,
               capture device channels 1+2 are always fed from mixer CH 1+2.

    ducker-off
               Turn the ducker off.

    ducker-on <INPUTS> <RELEASE>ms
               Turn the ducker on and set the following values:
                 INPUTS (range 0..15) is a bitmask for the input "selection"
                         0b0000 =  0 = no inputs watched
                         0b1111 = 15 = all four inputs watched
                 RELEASE (range 0..5000) is a the "release" time in ms
                         0 = release time 0, 5000 = release time 5000ms=5s

    ducker-range <HEX_VALUE>|<RANGE>dB
               Set the "duck range" to the given value.
               Valid range is 0dB to 90dB, or 0 to 0x1fffffff.
               It may be best to only use this while ducker is on.

    ducker-threshold <HEX_VALUE>|<THRESH>dB
               Set the "threshold" to the given value.
               Valid range is -60dB to 0dB, or 0x000000 to 0x7fffff.
               It may be best to only use this while ducker is on.

    meter
               Show the meter until you press Ctrl-C
               It may be best to only use this while ducker is on.

Build Requirements

For building scnp-cli, you need at least

clang or gcc
make (GNU make is helpful)
libusb-1.0.pc (from OS package like libusbx-devel or libusb-1.0-0-dev)
pkg-config command (from pkg-config or pkgconf package)
strongly recommended: bash-completion

For building from a git source tree, you also need at least

git
automake
autoconf

Building

When building from a git source tree (or one of the github "release" tarballs (*.tar.gz) or zipfiles (*.zip), which I wholeheartedly recommend to NOT use):

autoreconf -vis .

Then you can run the usual build commands as if you had unpacked a proper dist tarball (*.tar.xz):

./configure
make
make install

or for an out of source tree build

mkdir _b && cd _b
../configure
make
make install

Note that you do not need to install scnp-cli to run it. Just run it from the build dir if that suits you better than installing it.

Note that if you run make check or make distcheck and there is actually a Notepad series mixer connected, one of the test cases will write to the device and possibly change its settings.

Device permission setup using udev

scnp-cli writes to the mixer device by opening the device special file connected to the mixer, which is called something like /dev/bus/usb/006/004 and by default cannot be written to by ordinary users.

So we need to tell the system that the next time a mixer device is plugged in, it should set the permissions of the device special file such that an ordinary user can access it.

To help with that, we have two udev rules files:

70-soundcraft-notepad.rules Uses the TAG+="uaccess" mechanism to allow access users locally logged into a login session.
80-soundcraft-notepad.rules Sets the device file's group to audio to allow all group members access.

Check whether these udev rule files are suitable for your system before installing them. You can very well have both installed at the same time.

We have two special make targets to help with installing and uninstalling the udev rules files to the well-known system directory for udev rules /etc/udev/rules.d for local installations:

sudo make install-udev-rules
sudo make uninstall-udev-rules

If you package scnp-cli (e.g. as *.deb or *.rpm), I suggest you change the usual make install command to install the udev rules similar to the following command:

make DESTDIR=... udevrulesdir=/usr/lib/udev/rules.d install install-udev-rules