Update documentation for Scarlett 4th Gen and Vocaster

docs/iface-small.md

@@ -0,0 +1,56 @@
+# ALSA Scarlett2 Control Panel
+
+## Small Scarlett 3rd Gen Interfaces
+
+The Scarlett 3rd Gen Solo and 2i2 interfaces have just a few buttons to control
+the Air, Line, Phantom Power, and Direct Monitor settings. Mostly
+nothing that you can’t access from the front panel anyway.
+
+![Gen 3 Small Interfaces](../img/iface-small-gen3.png)
+
+## Input Controls
+
+### Air
+
+Enabling Air will transform your recordings and inspire you while
+making music.
+
+### Inst
+
+The Inst buttons are used to select between Mic/Line and Instrument
+level/impedance. When plugging in microphones or line-level equipment
+(such as a synthesizer, external preamp, or effects processor) to the
+input, set it to “Line”. The “Inst” setting is for instruments with
+pickups such as guitars.
+
+### 48V (Phantom Power)
+
+Turning the “48V” switch on sends “Phantom Power” to the XLR
+microphone input(s). This is required for some microphones (such as
+condensor microphones), and damaging to some microphones (particularly
+vintage ribbon microphones).
+
+## Output Controls
+
+### Direct Monitor
+
+Direct Monitor sends the analogue input signals to the analogue
+outputs for zero-latency monitoring.
+
+On the 2i2, you have the choice of Mono or Stereo monitoring when you
+click the button. Mono sends both inputs to the left and right
+outputs. Stereo sends input 1 to the left, and input 2 to the right
+output.
+
+## Startup Controls
+
+#### Phantom Power Persistence
+
+By default, phantom power is turned off when the interface is turned
+on. This can be changed in the startup configuration (menu option View
+→ Startup).
+
+The one control not accessible from the front panel is “Phantom Power
+Persistence” (menu option View → Startup) which controls the Phantom
+Power state when the interface is powered on.
+