From: Steinar H. Gunderson Date: Tue, 8 Nov 2016 18:02:24 +0000 (+0100) Subject: Start the audio node. X-Git-Url: https://git.sesse.net/?p=nageru-docs;a=commitdiff_plain;h=403d734c4564e560a85e329fccaf93700b4c1794 Start the audio node. --- diff --git a/audio.rst b/audio.rst index 050f8aa..2aedd36 100644 --- a/audio.rst +++ b/audio.rst @@ -1,2 +1,79 @@ -Audio (not written yet) -======================= +Audio +===== + +Audio is the most important part of video. It is also the most +neglected part in most amateur productions; it is easy to care +about full-HD productions but never remember to give the speaker +a microphone. Your stream can live with blurry or murky pictures, +but it cannot live with people not hearing what's being said. + +Nageru aims to give the operator meaningful, useful controls for +processing and mixing audio, with a focus on voice. There are two +modes for audio processing, namely *simple* and *multichannel*; +they are selectable from the audio menu. + +Be aware that a mix that sounds good on a PA system will not +necessarily sound good on a stream; PA systems often have rather +different audio characteristics than a set of home speakers or +headphones, and there will also frequently be other sounds in the +room that remove some of the typical “dryness”. However, for simple +use, reusing such a mix isn't the worst choice you can make. + + +Simple mode +----------- + +**Simple** audio mode is the default, and was the only mode available +up until Nageru 1.4.0. Despite its name, it contains a powerful +audio processing chain; however, in many cases, you won't need to +understand or twiddle any of the knobs availale. + +Simple mode allows input from only a single source, and that source +has to be one of the capture cards. (You choose which one by right-clicking +on its channel and selecting it as audio source.) The two typical +cases where this is useful are: + + * When you simply take in audio from one of the cameras, + possibly by way of external microphone, or + * When you have an external mixer and can embed its output + in one of the video inputs. + +If you want more than one audio source at a time, or if you want +to use ALSA inputs, you will need to use multichannel mode; it is +more complicated, but it is a strict superset of what the simple mode +can do. (In fact, simple mode constructs a multichannel setup +behind-the-scenes and then runs the multichannel audio code.) + + +The audio strip +--------------- + +.. image:: images/basic-ui.png + +The audio strip contains the processing chain for the audio from +start to end. Note that by default, everything is enabled; +if you have a premade audio mix that you are confident that you +want 1:1 into the stream, you can start Nageru with the “--flat-audio” +flag, that instead starts with everything disabled. + +The first step in the pipeline is a **lo-cut** (or equivalently, +highpass) filter. The exact cutoff frequency is a bit a matter +of taste (and also depends on the speaker), but the main point +is that it gets rid of low-frequency hum and a lot of the background +noise that is not related to the speaker's voice. (If you were +producing music, you'd probably want it there to make room for +music *under* it, but the you'd want it higher than the default 120 Hz.) + +(TODO: write more) + + +Audio meters +------------ + + +Multichannel mode +----------------- + + +MIDI control +------------ diff --git a/images/audio-strip.png b/images/audio-strip.png new file mode 100644 index 0000000..1dcf525 Binary files /dev/null and b/images/audio-strip.png differ