Write more about multichannel audio; adapted from my blog post.

diff --git a/audio.rst b/audio.rst
index 65fe9af432a20b130fd5ba81901eeebd87051720..ea949839ffcd2d963e838fdd1efc1f9f2ee73137 100644 (file)
--- a/audio.rst
+++ b/audio.rst
@@ -117,6 +117,7 @@ are indications of common issues:
 A healthy stereo stream will usually have a correlation somewhere
 around 0.7–0.8, and this section is marked in green.
 
+.. _audio-strip:
 
 The audio strip
 ---------------
@@ -209,6 +210,7 @@ several buses. Each bus has a name (for instance, something like
 Nageru doesn't care what you write here, but the labels are useful
 for the operator.
 
+
 Input mappings
 ''''''''''''''
 
@@ -267,10 +269,62 @@ keys on the keyboard) allow you to select between two views:
 
 .. image:: images/audio-bus-controls.png
 
-There's one set each of these controls for every bus.
-
-(TODO: write more)
-
+(TODO: fix image)
+
+There's one set each of these controls for every bus. The most
+important parts of the mix are given the most screen estate,
+so even though the way through the signal chain is left-to-right
+top-to-bottom, we'll go over it in the opposite direction.
+
+By far the most important part is the audio level, so the **fader** naturally is
+very prominent. (Note that the scale is nonlinear; you want more resolution
+in the most important area.) Changing a fader with the mouse or keyboard is
+possible, and probably most people will be doing that, but Nageru also
+supports USB faders (see :ref:`midi-control`). There's a mute button
+if you just want to silence a bus temporarily; it has exactly the same
+effect as pulling the fader all the way down, ie., it will make the bus
+go all silent.
+
+Then there's the **peak meter** to the left of that. For each bus, unlike
+for the meters used for mastering (see :ref:`audio meters`),
+you don't want to know loudness; you want to know recording levels,
+so this is a peak meter, *not* a loudness meter. (There's some holdoff
+so you can see the actual peaks over a short period.) In particular,
+you don't want the bus to send clipped data to the master
+(which would happen if you set it too high); Nageru can handle
+this situation pretty well (unlike most digital mixers, it mixes in
+full 32-bit floating-point so there's no internal clipping,
+and the limiter described in :ref:`audio-strip` will usually save you)
+but it's still not a good place to be in, so if you peak,
+the **historical peak label** under the meter will go red if it happens.
+If you want to reset it, click on it using the mouse.
+
+The peak meter doubles as an input peak check during
+setup; if you turn off all the effects and set the fader to neutral, you can
+see if the input hits peak or not, and then adjust it down. Left and right
+channel are shown separately, so you can see if they are approximately
+the same level or even completely mono.
+
+The **compressor** is well-known from the simple audio mode, but in this view,
+it also has a **reduction meter**, so that you can see whether it kicks in or not.
+(This is also nonlinear, and each step is marked with number of decibels
+the compressor had to reduce the signal.) Most casual users
+would want to just leave the gain staging and compressor settings alone, but
+a skilled audio engineer will know how to adjust these to each speaker's
+antics—some speak at a pretty even volume and thus can get a bit of
+headroom, while some are much more variable and need tighter settings.
+
+Finally (or, well, first), there's the EQ section. The **lo-cut** is again
+well-known from the simple audio mode (the filter is separate for each
+bus, the cutoff **frequency** is the same across all buses),
+but there's now also a simple **three-band EQ** per bus. Simply ask the speaker
+to talk normally for a bit, and tweak the controls until it sounds good.
+People have different voices and different ways of holding the microphone,
+and if you have a reasonable ear, you can use the EQ to your advantage to
+make them sound a little more even on the stream. Either that, or just
+put it in neutral, and the entire EQ code will be bypassed.
+
+.. _midi-control:
 
 MIDI control
 ------------