Update docs and such for 1st Gen and big 4th Gen support
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Geoffrey D. Bennett
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docs/iface-4th-gen-small.md
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docs/iface-4th-gen-small.md
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# ALSA Scarlett Control Panel
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## Scarlett Small 4th Gen Interfaces
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This document describes how to use the ALSA Scarlett Control Panel
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with the small Scarlett 4th Gen interfaces:
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- Scarlett 4th Gen Solo, 2i2, and 4i4
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### Comparison with earlier Scarlett and Clarett Interfaces
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If you are familiar with the Scarlett 2nd and 3rd Gen interfaces or
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the Clarett interfaces, the major differences to the 4th Gen
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interfaces from the point of view of this software are:
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- The 4th Gen Solo and 2i2 interfaces have the full routing and mixing
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capabilities of the larger 2nd and 3rd Gen and Clarett interfaces
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(although the line outputs and the headphone outputs are still
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linked).
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- The 4th Gen 2i2 and 4i4 interfaces have software-controllable
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(“remote”) input gain controls.
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- The 4th Gen interfaces don’t have the output volume and mute
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controls that the 2nd and 3rd Gen and Clarett interfaces have.
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- The Air mode with Presence+Drive is implemented with a DSP which is
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separately routable.
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## Main Window
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The main window is divided into three sections:
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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 main window for the Solo and 2i2 interfaces is shown below; the
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4i4 interface is similar to the 2i2, but doesn’t have the Direct
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Monitor control, and can show the position of the front panel volume
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knobs.
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### Global Controls
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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. This should only ever briefly show “Unlocked” when the sample
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rate is changed as these interfaces can only use their internal clock.
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#### Power
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The 4i4 has a “Power” control that displays the power status. It can
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be “Fail”, “Bus”, or “External”. “Fail” means that the interface is
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not receiving sufficient power; please see the Scarlett 4i4 4th Gen
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User Guide for more information. “Bus” vs. “External” indicates
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whether the interface is receiving power from the second USB-C port
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(“External”) or not (“Bus”).
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#### Sample Rate
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Sample Rate is informative only, and displays the current sample rate
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if the interface is currently in use. In ALSA, the sample rate is set
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by the application using the interface, which is usually a sound
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server such as PulseAudio, JACK, or PipeWire.
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### Analogue Input Controls
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The analogue input controls available depend on the interface model:
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- **Instrument, Air, and Phantom Power**: All models
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- **Mix**: Solo only (described later in the [Solo Mix
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Control](#solo-mix-control) section)
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- **Input Select, Link, Gain, Autogain, and Safe**: 2i2 and 4i4
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#### Instrument
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The Inst button(s) 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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(such as a synthesizer, external preamp, or effects processor) to the
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input, set it to “Line”. The “Inst” setting is for instruments with
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pickups such as guitars.
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#### Air
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The Scarlett 3rd Gen introduced Air mode which transformed your
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recordings and inspired you while making music by boosting the
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signal’s high-end. The 4th Gen interfaces now call that “Air Presence”
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and add a new mode “Air Presence+Drive” which boosts mid-range
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harmonics in your sound.
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#### Phantom Power (48V)
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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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The 2i2 has a single 48V switch that controls both channels, and the
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4i4 has an independent 48V switch for each channel.
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#### Input Select
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The 2i2 and 4i4 interfaces have hardware buttons for 48V, Inst, Air,
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Auto, and Safe. The “Input Select” control allows you to choose which
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channel those buttons control.
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#### Link
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The “Link” control links the 48V, Inst, Air, Auto, and Safe controls
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together so that they control both channels simultaneously.
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#### Gain
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The “Gain” controls adjust the input gain for the selected channel.
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Click and drag up/down on the control to adjust the gain, use your
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mouse scroll wheel, or click the control to select it and use the
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arrow keys, Page Up, Page Down, Home, and End keys.
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#### Autogain
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When the “Autogain” control is enabled, the interface will listen to
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the input signal for ten seconds and automatically adjust the gain to
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get the best signal level. When autogain is not running, the
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most-recent autogain exit status is shown below the “Autogain”
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control.
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#### Safe
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“Safe” mode is a feature that automatically reduces the gain if the
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signal is too loud. This can be useful to prevent clipping.
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### Analogue Output Controls
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The analogue output controls available depend on the interface model:
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- **Direct Monitor**: Solo and 2i2
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- **Volume Knobs**: 4i4
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#### Direct Monitor
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Enabling Direct Monitor sends the analogue input signals to the
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analogue outputs (speakers/headphones) for zero-latency monitoring.
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On the 2i2, you have the choice of Mono or Stereo monitoring when you
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click the button:
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- **Mono** sends both inputs to the left and right outputs
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- **Stereo** sends input 1 to the left, and input 2 to the right
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output.
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As the 4th Gen Solo and 2i2 interfaces have the full routing and
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mixing capabilities of the larger 2nd and 3rd Gen interfaces, the
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Direct Monitor levels can be [adjusted in the
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mixer](#solo-direct-monitor).
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The 4i4 has no Direct Monitor button, but that functionality can be
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achieved with [appropriate configuration in the routing and mixing
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windows](#4i4-sample-direct-monitor-configuration).
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#### Volume Knobs
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The 4i4 interface has volume knobs on the front panel, the position of
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which is shown in the main window.
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## Routing and Mixing
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The routing and mixing capabilities of the 4th Gen interfaces are the
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same in concept as the 2nd and 3rd Gen interfaces, but there is a DSP
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which is separately routable, and the default routing uses the mixer
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extensively.
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From the main window, open the Routing window with the View → Routing
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menu option or pressing Ctrl-R:
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To understand the signal flow, note the following:
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1. The Analogue 1 & 2 Inputs (i.e. the Mic/Line/Inst inputs) are
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routed to the DSP Inputs.
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2. The DSP Outputs are routed to the PCM 1 & 2 Inputs (that’s what
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ALSA sees as the first two inputs from the interface for
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recording).
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3. The PCM Outputs (that’s what ALSA sees as the interface outputs for
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playback) and the DSP Outputs are all connected to the Mixer
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Inputs.
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4. The Mixer A & B Outputs are connected to the Hardware Analogue
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outputs (i.e. your speakers/headphones) so you can hear any mix of
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the PCM and DSP Outputs (this is how the Direct Monitor function
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works).
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5. The Mixer C & D Outputs are connected to the PCM 3 & 4 Inputs (this
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is referred to as Loopback, for recording audio from your computer,
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but can be used for another purpose if you want).
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Important Notes:
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- The “Presets” are generally not useful with the 4th Gen interfaces
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as they are designed for the 2nd and 3rd Gen interfaces. If you try
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these out, you’ll probably want to reset back to the factory
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defaults afterwards.
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- Besides Air Mode, the DSP is also used for the gain halo level
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meters and autogain, so if you route something else to the DSP
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Inputs, those features will work “rather differently”.
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- The Focusrite Control 2 software can’t control most of this routing,
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so if you make changes here and then want to use Focusrite Control
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2, you’ll probably need to reset the routing back to the factory
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default settings.
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To adjust the routing:
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- Click and drag from a source to a sink or a sink to a source to
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connect them. Audio from the source will then be sent to that sink.
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- Click on a source or a sink to clear the links connected to that
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source/sink.
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Note that a sink can only be connected to one source, but one source
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can be connected to many sinks.
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To adjust the mixer output levels:
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1) Open the mixer window with the main window View → Mixer menu
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option, or press Ctrl-M.
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2) Mixer levels can be adjusted with your keyboard or mouse in the
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same way as the [Gain Controls](#gain).
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### Solo Direct Monitor
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When you enable or disable Direct Monitor on the Solo interface, the
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interface will update the Mix A and B Outputs so that the DSP 1 & 2
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Outputs are mixed in (or not) with the PCM 1 & 2 Outputs. Note how the
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volume of the PCM outputs is also reduced when Direct Monitor is
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enabled so that you can hear the DSP outputs (i.e. your Analogue
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inputs) more clearly.
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If you customise the Mix A/B mixer levels while Direct Monitor is
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enabled, the new settings will be saved and used when Direct Monitor
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is enabled again.
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### 2i2 Direct Monitor
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Similarly to the Solo interface, the 2i2 interface will update the Mix
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A and B Outputs when you enable or disable Direct Monitor, but the 2i2
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has Mono and Stereo options:
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Note how in Mono mode:
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- the DSP 1 & 2 Outputs are mixed to both the left and right outputs
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and in Stereo mode:
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- DSP 1 (i.e. Analogue Input 1) is sent to the left output (Mix A),
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and
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- DSP 2 (i.e. Analogue Input 2) is sent to the right output (Mix B).
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### Solo Mix Control
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The Mix control is only available on the Solo interface. It switches
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the source for the PCM 1 & 2 Inputs between the DSP Outputs and the
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Mixer E & F Outputs.
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By default, enabling this control will mix the Analogue 1 & 2 Inputs
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together before they are sent to the PCM 1 & 2 Inputs:
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This can be useful if you want to treat the PCM 1 & 2 Inputs as a
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stereo pair, and not have the line/instrument input panned hard left
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and the microphone input panned hard right.
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The mixer levels for the Mix E & F Outputs can adjusted to suit.
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### 4i4 Routing and Mixing
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Although the 4th Gen 4i4 has no explicit Direct Monitor control, it is
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far more flexible because it has 6 PCM inputs, 6 PCM outputs, a 10×6
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mixer, and 6 Analogue Hardware outputs.
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Analogue Outputs 1–4 correspond to the Line Outputs 1–4 on the back of
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the interface, and Analogue Outputs 5–6 correspond to the Headphone
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Output on the front of the interface.
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The default routing and mix for the 4i4 is shown below:
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Note that with the default routing/mix settings:
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- The Analogue Inputs 1–4 are routed to the PCM Inputs 1–4 (the first
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two going via the DSP).
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- PCM Inputs 5–6 are used for Loopback (recording audio from your
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computer).
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- All the Hardware Inputs and PCM Outputs are connected to the Mixer
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Inputs.
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- PCM Outputs 1–4 are connected to the Analogue Outputs 1–4 (via the
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mixer).
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- The Line 1–2 Outputs (Analogue Outputs 1–2) and the Headphones
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(Analogue Outputs 5–6) share the Mixer Outputs A & B.
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#### 4i4 Sample Direct Monitor Configuration
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A common configuration for the 4i4 is to send the PCM 1 & 2 Outputs
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mixed with the Analogue Inputs 1 & 2 to the Headphones, while leaving
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the Analogue Outputs 1–2 as they are. This is an advanced version of
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the direct monitoring feature that is available on the Solo and 2i2.
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It can be implemented by:
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1) Route Mixer Outputs E & F to Analogue Outputs 5 & 6.
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2) Turn up Mix E & F DSP 1 & 2 levels in the mixer (see the mixer
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example above for [2i2 Direct Monitor](#2i2-direct-monitor)).
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As there are only 6 Mixer Outputs, the PCM 5 & 6 Inputs (Loopback) are
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now shared with the headphones. If you want to retain the Loopback
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functionality without having the Analogue Inputs mixed in, you could:
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- Route the PCM 1 & 2 Outputs directly to the PCM 5 & 6 Inputs, rather
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than going via the mixer, or
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- Free up Mixer Outputs A & B for Loopback by routing PCM Outputs 1 &
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2 directly to Analogue Outputs 1 & 2.
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Besides Direct Monitor, there are many other possibilities for
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routing/mixing with the 4i4. For example, by using the additional PCM
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Outputs and Inputs you could set up a mix-minus configuration for a
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podcast/video call.
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## Levels
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The meters show the levels seen by the interface at every routing
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sink: Hardware Outputs, Mixer Inputs, DSP Inputs, and PCM Inputs. Open
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this window by selecting the View → Levels menu option or pressing
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Ctrl-L.
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Look at this in conjunction with the routing window to understand
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which meter corresponds to which source or sink.
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Thanks for reading this far! If you appreciate the hundreds of hours
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of work that went into the kernel driver, the control panel, and this
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documentation, please consider supporting the author with a
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[donation](../README.md#donations).
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