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Merge pull request #380 from perladvent/2023-12-18
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2023-12-18
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oalders authored Dec 16, 2023
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Expand Up @@ -2,7 +2,6 @@ Author: Joel Roth <joelz@pobox.com>
Title: Trimming audio files with Audio::Nama
Topic: Audio::Nama


=for :html
<center><img src="warpedwav7.png" alt="Warped audio waveforms" width="85%"></center>

Expand All @@ -15,36 +14,36 @@ various info breaks during a radio play. In other words, we
want to extract relevant parts of an audio file, and stitch
them together into a new file. We'll see how this happens
through an audio network language we'll use perl to
generate.
generate.

=head2 Our hammer

We'll be accomplishing this with Audio::Nama, a multitrack
We'll be accomplishing this with L<Audio::Nama>, a multitrack
recording mixing and audio-processing application written in
perl, and L<Ecasound|https://ecasound.seul.org/ecasound/>, a
general-purpose audio engine. We also need git, which Nama
uses to manage project state, provide for branching, undo,
etc. C<nama> is the executable program script and also man
page, so "man nama" for the docs, or use nama's internal
help.
help.

Nama configures Ecasound for recording, mixing and a variety
of tasks via a audio network definition called a I<chain
setup> with syntax we will use Nama to generate.
setup> with syntax we will use Nama to generate.

Aside from housekeeping duties, Nama's main task is to
regenerate the chain setup (and re-configure the engine)
whenever the graph changes due to user input, such
whenever the graph changes due to user input, such
as deactivating a track or changing an output--a bit
like how a spreadsheet recalculates as necessary.
like how a spreadsheet recalculates as necessary.

The first run of C<nama> creates a C<$HOME/nama> directory for
project files and a configuration file C<$HOME/.namarc>.
The first run of C<nama> creates a C<$HOME/nama> directory for
project files and a configuration file C<$HOME/.namarc>.

Nama assumes a linux environment: that you'll be recording
or listening from the default ALSA soundcard device,
or listening from the default ALSA soundcard device,
usually your computer's built-in soundcard. You can
change this setting in C<namarc>.
change this setting in C<namarc>.

=for :html
<center><img src="thin2.png" alt="section divider" width="7%"></center>
Expand All @@ -56,15 +55,15 @@ We'll create a new project called 'christmas'.
C<$ nama -c christmas>

We get a startup banner, then an empty track listing:

No. Name Requested Status Source Destination Vol Pan
===============================================================================
1 Main MON Main bus CH 1/2 100 50
2 Mixdown OFF track Main -- -- --

nama christmas Mixdown >

In the prompt, 'christmas' is the project, 'Mixdown', the current track.
In the prompt, 'christmas' is the project, 'Mixdown', the current track.

We create a separate track to accommodate our audio file,
then import the file.
Expand All @@ -81,14 +80,14 @@ then import the file.
2 Mixdown OFF track Main -- -- --
3 carol PLAY carol_1.wav Main bus 100 50

We can now press SPACE to start/stop playback.
We can now press SPACE to start/stop playback.

In the track listing above we see that track 'carol' with
source C<carol_1.wav> is set to PLAY. The output of 'carol'
feeds the 'Main' track via the 'Main' bus. The 'Main' track
serves as the master fader with output to the sound card.
Like 'carol', all new tracks start as members of the 'Main'
bus.
bus.

=for :html
<center><img src="thin2.png" alt="section divider" width="7%"></center>
Expand All @@ -102,14 +101,14 @@ keep.

We do that by listening to the track and using the
C<clip-here> command (bound to the F1 key) to mark clip
starts and ends.
starts and ends.

After some trial and error, we have the correct marks.
In this example: four five-minute sections of content
separated by 40-second breaks.

nama christmas carol > list-marks

0 40.0 clip-start-0020
1 340.0 clip-end-0021
2 380.0 clip-start-0022
Expand All @@ -134,7 +133,7 @@ We can now assemble our clips.

Note that the source for track 3 has changed from C<carol_1.wav> to
C<carol sequence>.

Having listened to the output and resolved any hiccups
(there were none!) we are ready to render it to an audio
file.
Expand Down Expand Up @@ -168,9 +167,9 @@ The mixdown step also generates ogg and mp3 encodings with
oggenc and lame, respectively, if desired. These files
appear in the project directory:

C<~/nama/christmas/christmas_1.mp3>
C<~/nama/christmas/christmas_1.ogg>
C<~/nama/christmas/christmas_1.wav> is a symlink to C<~/nama/christmas/.wav/Mixdown_1.wav>
C<~/nama/christmas/christmas_1.mp3>
C<~/nama/christmas/christmas_1.ogg>
C<~/nama/christmas/christmas_1.wav> is a symlink to C<~/nama/christmas/.wav/Mixdown_1.wav>

=for :html
<center><img src="thin2.png" alt="section divider" width="7%"></center>
Expand All @@ -183,7 +182,7 @@ An Ecasound chain setup is made of signal-processing
I<chains>--edges in the processing graph--and I<loop
devices>, which are nodes capable of summing their inputs.

A chain represents a stream with one input and one output.
A chain represents a stream with one input and one output.

Here is a setup of one chain, omitting general options
related to buffer sizes, etc.
Expand All @@ -206,9 +205,9 @@ loop device. A loop device is a buffer stage that can sum
the signal from one or more chains. It supplies the sum to
another chain (or possibly multiple chains.) A loop device
with its sources and an output chain can represent a mixer
or bus.
or bus.

Significantly for our task, a chain can represent an I<audio clip>,
Significantly for our task, a chain can represent an I<audio clip>,
part of an audio file that plays at a particular time.

-a:5 -f:s16_le,2,44100 -i:playat,40,select,80,300,/home/jroth/nama/christmas/.wav/carol_1.wav
Expand All @@ -222,7 +221,7 @@ plugins and plugin controllers called I<chain operators>
included in Ecasound and provided by numerous
L<LADSPA|https://ladspa.org> and
L<LV2|https://wiki.linuxaudio.org/apps/categories/lv2_plugins>
authors.
authors.

=for :html
<center><img src="thin2.png" alt="section divider" width="7%"></center>
Expand All @@ -233,7 +232,7 @@ Each time a change in track status occurs, Nama generates a
Chain setup file and commands Ecasound to load it.

Let's start with the mixer configuration when we imported
our radio play.
our radio play.

No. Name Requested Status Source Destination Vol Pan
===============================================================================
Expand All @@ -242,7 +241,7 @@ our radio play.
3 carol PLAY carol_1.wav Main bus 100 50

This is the corresponding chain setup:

nama christmas carol > chains

# audio inputs
Expand Down Expand Up @@ -312,34 +311,34 @@ chain setup: a different class for each type of terminal.
[1516] ChainSetup (L 362) name: Main, endpoint: Main_in, direction: input


bless( {
chain_id_ => 3,
endpoint_ => "wav_in",
track_ => "carol",
}, 'Audio::Nama::IO::from_wav' )
bless( {
chain_id_ => 1,
endpoint_ => "soundcard_out",
track_ => "Main",
}, 'Audio::Nama::IO::to_alsa_soundcard_device' )
bless( {
chain_id_ => 3,
device_id_ => "loop,Main_in",
endpoint_ => "Main_in",
track_ => "carol",
}, 'Audio::Nama::IO::to_loop' )
bless( {
chain_id_ => 1,
device_id_ => "loop,Main_in",
endpoint_ => "Main_in",
track_ => "Main",
}, 'Audio::Nama::IO::from_loop' )
bless( {
chain_id_ => 3,
endpoint_ => "wav_in",
track_ => "carol",
}, 'Audio::Nama::IO::from_wav' )

bless( {
chain_id_ => 1,
endpoint_ => "soundcard_out",
track_ => "Main",
}, 'Audio::Nama::IO::to_alsa_soundcard_device' )

bless( {
chain_id_ => 3,
device_id_ => "loop,Main_in",
endpoint_ => "Main_in",
track_ => "carol",
}, 'Audio::Nama::IO::to_loop' )

bless( {
chain_id_ => 1,
device_id_ => "loop,Main_in",
endpoint_ => "Main_in",
track_ => "Main",
}, 'Audio::Nama::IO::from_loop' )

These classes provide methods that can be overridden by
field values annotated on the graph edges or graph nodes,
field values annotated on the graph edges or graph nodes,
with the edge (chain) values having the highest priority.

Overrides are used for mixdown and anywhere values for an IO
Expand All @@ -352,7 +351,7 @@ track.
We'll look at the project after we issued the C<gather>
command and entered <mixdown>, ready to render the sequenced
clips. The output of track 'Main' feeds track 'Mixdown'
which will write C<Mixdown_1.wav>.
which will write C<Mixdown_1.wav>.

No. Name Requested Status Source Destination Vol Pan
================================================================================
Expand All @@ -376,7 +375,7 @@ The source for each is the same audio file.
7 carol-4-carol-v PLAY carol_1.wav carol sequen 100 50

In the chain setup below we see that C<select> and C<playat> terms
are used in the inputs to define a region of the audio file and play it
are used in the inputs to define a region of the audio file and play it
with a given delay. The values were generated from our list
of marks.

Expand All @@ -399,7 +398,7 @@ of marks.

Some overriding was involved, as we see C<-a:Mixdown>, a
chain identifier that is not a track number. I think there
was some technical reason, but it does stand out.
was some technical reason, but it does stand out.

=head2 Thanks for reading!

Expand Down

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