From: Steinar H. Gunderson Date: Wed, 9 Nov 2016 19:46:31 +0000 (+0100) Subject: Write more about audio. X-Git-Url: https://git.sesse.net/?p=nageru-docs;a=commitdiff_plain;h=d7d47cba9a794efe23d4ac53f108628ca221935f Write more about audio. --- diff --git a/audio.rst b/audio.rst index e1b8d19..65fe9af 100644 --- a/audio.rst +++ b/audio.rst @@ -45,6 +45,8 @@ can do. (In fact, simple mode constructs a multichannel setup behind-the-scenes and then runs the multichannel audio code.) +.. _audio-meters: + Audio meters ------------ @@ -171,12 +173,104 @@ that got through the other compressors—a classic example is a speaker suddenly coughing, or a very loud bass drum. This prevents both clipping and blowing out the speakers' ears. -(TODO: write more) +At this point, the audio signal is *almost* where we'd like it +to be, but the overall sound level might not be quite right. +All the previous compressors have been working in the objective +domain, but as explained in the :ref:`previous section `, +this does not necessarily correspond to the desired overall +audio loudness. (Their default levels have been calibrated so +that they end up around 0 LU for typical speech content, +but they could easily miss by a few LU in many cases.) + +Thus, there's a final **makeup gain** at the end to compensate +for these issues. When the “Auto” checkbox is ticked, which is +by default, it will very slowly (filter constant of 30 seconds) +adjust itself so that the overall level goes toward 0 LU, +ie., the reference level. It is so slow because the R128 calculations +inherently must go over a certain amount of time (what we want +to change with this gain is the *overall* sound level, +not the *immediate* one). In periods where the makeup gain is +far off, such as when the stream is all silent, it doesn't update +at all. As with the other knobs, you can uncheck the “Auto” +checkbox and tune this yourself if you want to. Multichannel mode ----------------- +**Multichannel mode** expands on simple audio mode by allowing you +to have multiple *buses* of audio. (In a sense, it could more accurately +be called “multibus mode” instead, but the name would be too confusing.) +A bus in Nageru is a pair of channels (left/right), sourced from +a video capture or ALSA card. The channel mapping is flexible; my USB +sound card has 18 channels, for instance, and you can use that to make +several buses. Each bus has a name (for instance, something like +“Blue microphone” or “Speaker PC”), which is just for convenience; +Nageru doesn't care what you write here, but the labels are useful +for the operator. + +Input mappings +'''''''''''''' + +.. image:: images/input-mapping.png + +The input mapping dialog should be pretty much self-explanatory; +you can use the + button to add a new bus, and the - button to remove +the currently selected one (you select by clicking on it). The up and +down buttons rearrange the order by moving the currently selected bus +up or down, if possible. + +Because mappings can be tedious to setup, you wouldn't want to set up +a complicated one every time you started Nageru. Therefore, mappings +can be saved and loaded from disk; the stored file is a +`protocol buffer `_ +in textual format. You can also load one at start with the +“--input-mapping” parameter, which also implies multichannel mode +(--multichannel). + +Nageru strives to keep the mapping consistent even +in the face of a changed environment—for instance, if you unplug and +replug a USB sound card, Nageru will attempt to keep your buses mapped to +that card still mapped. (While the card unplugged, the main display will show +the relevant buses as “(disconnected)”.) Similarly, if an ALSA device +is taken by another program on startup and cannot be accessed by Nageru, +it will mark it as “(busy)” and try again in the background. However, +there are edge cases where Nageru simply cannot do the right thing, +for instance if you unplug two identical cards and plug them back +in the reverse order; USB cards don't carry any kind of serial number +or other forms of unique identification. + + +The audio views +''''''''''''''' + +.. image:: images/audio-view-selector.png + +Once multichannel mode is active, a little selector shows up to the right, +just below the level meters. The arrows (or equivalently, the PgUp/PgDown +keys on the keyboard) allow you to select between two views: + + * In the **compact audio view** (which is the default), each bus is + represented only by its label, its peak meter (see below) and its + fader. This takes up little screen estate, and allows the video channels + to be visible. This is the typical view you'd use once you've set up + everything and are actually doing live video editing; the controls + from the full audio view are still in effect, but you cannot see or + interact with them. + + * The **full audio view** contains a lot more controls, but leaves no + room for the video channels. These are useful when you are doing initial + setup of your mix, or if you want to go back and tune something. + The full audio view will be described in detail in the following section; + the interpretation of the corresponding controls in the compact audio view + is the same. + +.. image:: images/audio-bus-controls.png + +There's one set each of these controls for every bus. + +(TODO: write more) + MIDI control ------------ diff --git a/images/audio-view-selector.png b/images/audio-view-selector.png new file mode 100644 index 0000000..328608b Binary files /dev/null and b/images/audio-view-selector.png differ diff --git a/images/input-mapping.png b/images/input-mapping.png new file mode 100644 index 0000000..50e9c53 Binary files /dev/null and b/images/input-mapping.png differ diff --git a/images/level-meters.png b/images/level-meters.png new file mode 100644 index 0000000..13185ca Binary files /dev/null and b/images/level-meters.png differ