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This commit is contained in:
Geoffrey D. Bennett
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USAGE.md
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# ALSA Scarlett Gen 2/3 Control Panel Usage
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## Prerequisites
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Linux Kernel with the ALSA Scarlett Gen 2/3 mixer driver. Use at least
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version 5.14 for Scarlett Gen 3 support and bug fixes for the Gen 2
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support.
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As of Linux 5.17, the driver is still disabled by default and needs to
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be enabled at module load time with the `device_setup=1` option to
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insmod/modprobe. Create a file /etc/modprobe.d/scarlett.conf
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containing the appropriate line for your device:
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Gen 2:
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- 6i6: `options snd_usb_audio vid=0x1235 pid=0x8203 device_setup=1`
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- 18i8: `options snd_usb_audio vid=0x1235 pid=0x8204 device_setup=1`
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- 18i20: `options snd_usb_audio vid=0x1235 pid=0x8201 device_setup=1`
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Gen 3:
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- Solo: `options snd_usb_audio vid=0x1235 pid=0x8211 device_setup=1`
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- 2i2: `options snd_usb_audio vid=0x1235 pid=0x8210 device_setup=1`
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- 4i4: `options snd_usb_audio vid=0x1235 pid=0x8212 device_setup=1`
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- 8i6: `options snd_usb_audio vid=0x1235 pid=0x8213 device_setup=1`
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- 18i8: `options snd_usb_audio vid=0x1235 pid=0x8214 device_setup=1`
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- 18i20: `options snd_usb_audio vid=0x1235 pid=0x8215 device_setup=1`
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Or you can use a sledgehammer:
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```
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options snd_usb_audio device_setup=1,1,1,1
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```
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to pass that option to the first 4 USB audio devices.
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To see if the driver is present and enabled: `dmesg | grep -i -A 5 -B
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5 scarlett` should display information like:
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```
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New USB device found, idVendor=1235, idProduct=8215, bcdDevice= 6.0b
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Product: Scarlett 18i20 USB
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Focusrite Scarlett Gen 2/3 Mixer Driver enabled pid=0x8215
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```
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If the driver is disabled you’ll see a message like:
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```
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Focusrite Scarlett Gen 2/3 Mixer Driver disabled; use options
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snd_usb_audio vid=0x1235 pid=0x8215 device_setup=1 to enable and
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report any issues to g@b4.vu",
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```
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## Building and Running
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On Fedora, the packages `alsa-lib-devel` and `gtk4-devel` need to be
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installed:
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```
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sudo dnf -y install alsa-lib-devel gtk4-devel
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```
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To build:
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```
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cd src
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make -j4
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```
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To run:
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```
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./alsa-scarlett-gui
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```
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## No interface connected
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If no interface is detected (usually because there isn’t one
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connected!) you’ll see this window:
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Plug in an interface or select the menu option File → Interface
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Simulation and load a demo file to make more interesting things
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happen.
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## MSD (Mass Storage Device) Mode
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If MSD Mode is enabled (as it is from the factory), you need to
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disable it and restart your interface to get access to its full
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functionality.
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## Using on Small Interfaces
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For the small Gen 3 interfaces (Solo and 2i2), there’s just a few
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buttons to control the Air, Line, Phantom Power, and Direct Monitor
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settings. Mostly nothing that you can’t access from the front panel
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anyway.
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The Line/Inst (Level), Air, and 48V controls are described below in
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the Analogue Input Controls section.
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Direct Monitor sends the analogue input signals to the analogue
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outputs for zero-latency monitoring. On the 2i2, you have the choice
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of Mono or Stereo monitoring. Mono sends both inputs to the left and
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right outputs. Stereo sends input 1 to the left, and input 2 to the
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right output.
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The one control not accessible from the front panel is “Phantom Power
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Persistence” (menu option View → Startup) which controls the Phantom
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Power state when the interface is powered on.
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## Gen 2 6i6+ and Gen 3 4i4+ Interfaces
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The Gen 2 6i6+ and Gen 3 4i4+ interfaces have many controls available.
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The controls are split between 4 windows, 3 of which are by default
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hidden.
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The main window has:
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- Global Controls
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- Analogue Input Controls
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- Analogue Output Controls
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The View menu option on the main window lets you open three other
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windows which contain the other controls:
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- Routing
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- Mixer
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- Startup
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### Global Controls
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Global controls affect the operation of the interface as a whole.
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#### Clock Source
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Clock Source selects where the interface receives its digital clock
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from. If you aren’t using S/PDIF or ADAT inputs, set this to Internal.
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#### Sync Status
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Sync Status indicates if the interface is locked to a valid digital
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clock. If you aren’t using S/PDIF or ADAT inputs and the Sync Status
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is Unlocked, change the Clock Source to Internal.
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#### Speaker Switching (18i8 Gen 3 and 18i20 Gen 3 only)
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Speaker Switching lets you swap between two pairs of monitoring
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speakers very easily.
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When enabled (Main or Alt):
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- Line Out 1–4 Volume Control Switches are locked to HW
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- Line Out 3/4 routing is saved
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- Line Out 3/4 routing is set to the Line Out 1/2 routing
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When set to Main, Line outputs 3 and 4 are muted.
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When set to Alt, Line outputs 1 and 2 are muted.
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When disabled (Off):
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- Global mute is activated
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- Line Out 1–4 Volume Control Switches are unlocked
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- Line Out 3/4 routing is restored to the saved values
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#### Talkback (18i20 Gen 3 only)
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Talkback lets you add another channel (usually the talkback mic) to a
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mix with a button push, usually to talk to musicians, and without
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using an additional mic channel.
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The Talkback feature has a few parts:
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- Talkback Microphone connected to Analogue Input 9
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- Talkback Disable/Enable internal switch
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- Talkback Off/On physical switch
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- Talkback Mix (one switch per mix)
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- Mix Input 25
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To set up the talkback feature, set Mix Input 25 to the talkback
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source (usually Analogue Input 9), enable the Talkback Mix switches
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for the mixes you want the talkback input to be heard on, and change
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the Talkback control from Disabled to Off. Leave the Mix Input 25 gain
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controls at zero (−127dB), otherwise the talkback inputs will be heard
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even when talkback is disabled/off.
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Pressing the Talkback switch on the device will then lower the volume
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of the other inputs on the mixes for which talkback is enabled and
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unmute Mix Input 25 on those mixes.
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Talkback can also be activated by changing the Talkback control from
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Off to On.
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The talkback microphone can also be used just the same as any of the
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other analogue inputs and routed to a physical output, PCM input, or
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mixer input.
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### Analogue Input Controls
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This is applicable to all interfaces except the Gen 2 18i20 which has
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hardware-only buttons for these features.
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#### Level
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The Level buttons are used to select between Mic/Line and Instrument
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level/impedance. When plugging in microphones or line-level equipment
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to the input, set it to “Line”. The “Inst” setting is for instrument
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with pickups such as guitars.
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#### Air (Gen 3 only)
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Enabling Air will transform your recordings and inspire you while
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making music.
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#### Pad
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Enabling Pad engages an attenuator in the channel, giving you more
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headroom for very hot signals.
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#### Phantom Power (48V)
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Gen 2 devices have a hardware button for controlling phantom power.
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Gen 3 devices have hardware and software control of phantom power.
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Turning the “48V” switch on sends “Phantom Power” to the XLR
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microphone input. This is required for some microphones (such as
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condensor microphones), and damaging to some microphones (particularly
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vintage ribbon microphones).
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On Gen 3 device, phantom power is turned off by default when the
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interface is turned on. This can be changed in the startup
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configuration (menu option View → Startup).
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### Analogue Output Controls
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The analogue output controls let you set the output volume (gain) on
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the analogue line out and headphones outputs. All interfaces support
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setting the gain and muting individual channels.
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Click and drag up/down to change the volume, or use your mouse scroll
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wheel. You can also double-click on the volume dial to quickly toggle
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the volume between the minimum value and 0dB.
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The bigger interfaces: Gen 2 18i20, Gen 3 18i8, and Gen 3 18i20 have a
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switchable hardware/software volume control. The position of the big
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volume knob on the front of the interface is indicated by the “HW”
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dial in the GUI. The analogue outputs can have their volume set either
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by the knob (“HW” setting of of the HW/SW button) or by the dials on
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each output (“SW” setting of the HW/SW button).
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When set to HW, the mute/volume status for those channels is
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controlled by the hardware volume knob and the global dim/mute
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controls and the software volume dial and mute button for those
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channels are disabled.
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There are “mute” and “dim” (reduce volume) buttons below the “HW” dial
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which affect only the outputs with “HW” control enabled. The Gen 3
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18i8 doesn’t have physical buttons or indicator lights for these
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control, but the 18i20 devices do.
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On the other (smaller) interfaces, the big volume knob on the front of
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the interface controls the volume of the Line 1 and 2 outputs. This is
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in addition to the software volume control, therefore both must be
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turned up in order to hear anything. The other (line 3+) analogue
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outputs are only controlled by the software controls.
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The volume controls for the headphone outputs on each interface
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operate in addition to any other hardware or software volume controls
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for those channels. When using headphones, the volumes for those
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channels would usually be set to 0dB and the actual volume controlled
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with the physical headphone volume control(s).
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### Routing
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The routing window allows complete control of signal routing between
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the hardware inputs/outputs, internal mixer, and PCM (USB)
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inputs/outputs.
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To manage the routing connections:
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- Click and drag from a source to a destination or a destination to a
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source to connect them. Audio from the source will then be sent to
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that destination.
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- Click on a source or a destination to clear the links connected to
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that source/destination.
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Note that a destination can only be connected to one source, but one
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source can be connected to many destinations. If you want a
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destination to receive input from more than one source, use the mixer
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inputs and outputs.
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The Presets menu can be used to clear all connections, or to set up
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common configurations:
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- The “Direct” preset sets up the usual configuration using the
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interface as an audio interface by connecting:
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- all Hardware Inputs to PCM Inputs
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- all PCM Outputs to Hardware Outputs
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- The “Preamp” preset connects all Hardware Inputs to Hardware Outputs.
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- The “Stereo Out” preset connects PCM 1 and 2 Outputs to pairs of
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Hardware Outputs.
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The Direct routing configuration is the simplest most-generally-useful
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configuration:
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#### Loopback
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Gen 2 interfaces have as many PCM Inputs as Hardware Inputs. Gen 3
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interfaces have two more PCM Inputs which the proprietary driver
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restricts to being “Loopback” inputs.
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The “Loopback” feature advertised for Gen 3 devices is actually a
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limitation of the propretary Focusrite Control software. Both Gen 2
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and Gen 3 devices support full reassignment of the PCM Inputs, so you
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can have any PCM Input as a “Loopback” or assigned to any other
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source.
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#### Talkback
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The Gen 3 18i20 talkback microphone is Analogue Input 9 and can be
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routed like any other source. If you want to record using it, there is
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no need for the loopback hack suggested by the vendor. Just route it
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to a PCM Input.
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### Mixer
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If you use the Routing window to connect Sources to Mixer Inputs and
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Mixer Outputs to Destinations, then you can use the Mixer window to
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set the amount of each Mixer Input that is sent to each Mixer Output
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using a matrix of controls.
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Click and drag up/down on the gain controls to adjust, or use your
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mouse scroll wheel. You can also double-click on the dial to quickly
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toggle between the minimum value and 0dB.
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### Startup
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The Startup window is used to configure settings that only take effect
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when the interface is powered on.
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#### Standalone
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When Standalone mode is enabled, the interface will continue to route
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audio as per the previous routing and mixer settings after it has been
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disconnected from a computer. By configuring the routing between the
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hardware and mixer inputs and outputs appropriately, the interface can
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act as a standalone preamp or mixer.
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Standalone mode is supported on all devices supported by the kernel
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driver. Even the 4i4 Gen 3 (which is bus-powered) will operate in
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standalone mode.
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#### Phantom Power Persistence (Gen 3 only)
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When Phantom Power Persistence is enabled, the interface will restore
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the previous Phantom Power/48V setting when the interface is turned
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on. For the safety of microphones which can be damaged by phantom
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power, the interface defaults to having phantom power disabled when it
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is turned on.
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#### MSD (Mass Storage Device) Mode (Gen 3 only)
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When MSD Mode is enabled (as it is from the factory), the interface
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has reduced functionality. You’ll want to have this disabled. On the
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other hand, when MSD Mode is enabled, the interface presents itself as
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a Mass Storage Device (like a USB stick), containing a link to the
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Focusrite web site encouraging you to register your product and
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download the proprietary drivers which can’t be used on Linux.
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By default, once MSD Mode is disabled, the control for it is hidden.
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If for some reason you want to re-enable MSD Mode, you can set the
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`device_setup` option to 3 to get the control back.
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## Load/Save Configuration
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The entire state of the interface can be loaded and saved using the
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File → Load Configuration and File → Save Configuration menu options.
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Internally, this uses `alsactl`:
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- Load: `alsactl restore USB -f <fn>`
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- Save: `alsactl store USB -f <fn>`
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The saved state files can be used to simulate an interface if you
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don’t have one attached. The `demo` directory in the distribution
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contains a sample file for every supported model.
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## Interface Simulation Mode
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The GUI can load an `alsactl` state file saved from a real interface
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and display a GUI as if the corresponding interface was connected.
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This is useful if you don’t have an interface connected and want to
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try, develop, or debug the GUI.
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Either specify the `.state` filename on the command line or select the
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menu option File → Interface Simulation to load.
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## Known Bugs/Issues
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- The linear-dB scale of the volume controls doesn’t work well. Lower
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volumes (e.g. below −30dB) don’t need as much fine control as higher
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volumes.
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- Can’t select (focus) the gain/volume controls or use a keyboard to
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adjust them.
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- Level (monitoring) doesn’t work yet and is disabled (needs kernel
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driver update).
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- Load/Save uses `alsactl` which will be confused if the ALSA
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interface name (e.g. `USB`) changes.
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- Load/Save is not implemented for simulated interfaces.
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- Lots of “couldn't find weak ref” warnings are emitted when loading a
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state file for simulation.
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- The read-only status of controls in interface simulation mode does
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not change when the HW/SW button is clicked.
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- When there’s more than one main window open, closing one of them
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doesn’t free and close everything related to that card.
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- There is no facility to group channels into stereo pairs (needs
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kernel support to save this information in the interface).
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- There is no facility to give channels custom names (needs kernel
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support to save this information in the interface).
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Reference in New Issue
Block a user