website: Add draft about 1.2.0 release song.

* website/drafts/music-production-on-guix-system.md: New file.

website/drafts/music-production-on-guix-system.md

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+title: Music Production on Guix System
+date: 2020-11-24 23:00
+author: Ricardo Wurmus
+tags: Music
+---
+
+The recent release of Guix 1.2.0 was accompanied by a release song.
+Let me tell you how this happened and how you can use Guix System for
+your own music productions!
+
+It all started only three days before the 1.2.0 release when someone
+on the `#guix` IRC channel brought up the tradition of OpenBSD people
+to write, record, and publish at least one song alongside their system
+release:
+
+    https://logs.guix.gnu.org/guix/2020-11-20.log#142825
+
+A wistful look at my neglected instruments later I felt compelled to
+take this as a challenge: with less than three days to go could we
+actually compose, record, and publish a song using nothing but free
+software despite a jam-packed weekend schedule?  I wanted to find out.
+
+## Inspiration and Planning
+
+The working title "Ode to One Two Oh" was an obvious choice, being a
+quasi-palindrome, and its five syllables suggested a time signature of
+5/4.  Where to from here?
+
+As I stared at my Emacs session with a Guile REPL (read, eval, print,
+loop) buffer I tried to recall what the letters "REPL" stand for.
+Clearly, in my case the "P" was for "Procrastination", but what about
+the others?  I had stumbled upon the chorus: a description of the Guix
+development process.  Contribute as others before us have shared their
+contributions ("Reciprocation"), review patches and discuss
+("Evaluation"), hack on something else ("Procrastination"), and repeat
+("Loop").
+
+The words suggested a simple descending melody, which would need to be
+elevated by a somewhat less simple chord progression.  After trying
+out a few harmonies on the Grand Stick I remembered how terrible my
+memory was and decided that I would need to scatter the harmonies onto
+a canvas, listen to the whole progression, and adjust the lines as
+needed --- all *without* having to build up muscle memory for
+harmonies and progressions I may very well end up discarding in the
+process.
+
+This is where my composition workflow probably deviates from most
+other people.  Many would use a MIDI sequencer for that kind of
+approach, whereas I decided to hone in on the exact harmonies with an
+unlikely tool: the unparalleled [music engraving application
+Lilypond](https://lilypond.org/).  Lilypond sports a versatile
+language that covers primitive note input, the means of combining them
+to larger phrases and musical ideas, and the means of abstraction ---
+it allows for musical ideas to be named and recombined in different
+shapes.  For everything the language doesn't account for with
+specialized syntax I can simply switch to Guile Scheme.  No other
+notation software is as flexible and malleable as Lilypond.  I let it
+generate both sheet music and a MIDI file --- the sheet music is
+displayed in a PDF viewer in Emacs and the MIDI file sent to
+`fluidsynth` (because I trust my ears over my eyes).
+
+    lilypond draft.ly && \
+      fluidsynth -r 48000 -i -n -a alsa \
+        ~/soundfonts/FluidR3GM.sf2 draft.midi
+
+I always try to keep the duration of my stay in the MIDI world at a
+minimum, because a composition workflow that is firmly rooted in MIDI
+tends to result in music that sounds sterile or robotic, an
+undesirable quality that can be hard to eradicate later.  So I put
+them aside and focus on another part of the song.  Mirroring the
+quasi-palindrome of the title, the song's structure would be A B C B
+A.  With the smooth chords of the B section locked down I walked up to
+the Grand Stick (I mounted it on a modified microphone stand for more
+flexibility) and tapped out a contrasting two-handed funky bass line
+to the click of a metronome.
+
+Time to record!
+
+## Audio Recording
+
+How does the signal of my stringed instrument make it into a file on
+my computer's disk?  The Stick's stereo signal feeds into two
+daisy-chained [Axoloti boards](http://www.axoloti.com/) with
+[hand-crafted](https://guix.gnu.org/en/packages/axoloti-patcher-1.0.12-2/)
+signal processing tuned to the peculiarities of my instrument; the
+stereo output of the DSP boards is connected to two inputs on my USB
+audio interface (the Tascam US16x08, though any class-compliant audio
+interface will work just fine), which presents itself to the system as
+a 16 channel input sound card.  The computer runs [JACK
+1](https://guix.gnu.org/en/packages/jack-0.125.0/) to shuffle the
+incoming signals on all channels to other JACK clients (audio
+applications and plugins).  I use
+[patchage](https://guix.gnu.org/en/packages/patchage-1.0.2/) to
+conveniently wire up inputs and outputs in an interactive graphical
+signal flow diagram.
+
+The center piece of my recording session is the venerable
+[Ardour](https://guix.gnu.org/en/packages/ardour-5.12/), an incredibly
+flexible and polished digital audio workstation (DAW) that natively
+supports JACK and also serves as an [LV2](https://lv2plug.in/) audio
+plugin host.
+
+Okay, the Stick is ready to be recorded, but I prefer to record a drum
+track first instead of playing to the click of a metronome.  But wait,
+I really can't record the drums now!  This is an apartment and the
+neighbors are asleep.  Oh, and I'm a lousy funk drummer.  Let's cheat!
+
+My drum machine of choice is
+[Hydrogen](https://guix.gnu.org/en/packages/hydrogen-1.0.1/).  It lets
+me create any numer of arbitrarily long patterns, combine them, and
+--- that's crucially important --- sync up with other JACK
+applications such as Ardour.  I toggled a button in Ardour to let it
+take control of the JACK transport, meaning that when I start
+recording in Ardour the drum machine starts playing in sync ---
+perfect!  Let's roll!
+
+## Rough Processing
+
+After frustrating minutes had turned into exhausting hours of
+recording the bass line (eventually resorting to punching in and out
+instead of re-recording *everything* whenever I made an audible
+mistake) I put my arranger's hat on and tried to get a sense for what
+might still be missing.  The recorded track sounded rather "flat";
+after all this was the "raw" signal straight from the instrument's
+pre-amplifier.  Time to spruce it up and approximate the final sound!
+
+Over the years the selection of audio plugins that I'm using to
+process my recordings has narrowed down to few more than the [Calf
+suite of LV2 plugins](https://guix.gnu.org/en/packages/calf-0.90.3/).
+I will admit to being an extremely superficial person, so a big factor
+in choosing the Calf plugins is the consistent, very pretty and
+intuitive user interface they present.  What made me stick to the Calf
+plugins, though, is that they also sound really good.  Furthermore,
+they make it easy to tweak the many parameters and come with helpful
+diagnostics (such as listening only to the changed frequencies, or
+spectral visualizations, etc).
+
+First thing I do is to use light compression to even out slight
+variations in dynamics.  Calf Mono Compressor does the job here.  The
+principle is simple: a compressor *lowers* the volume when a sound
+gets loud and it *raises* the volume of the resulting signal according
+to the dialed in makeup gain.  It has a bunch of other knobs to
+control how far ahead it will look to watch out for loud sounds,
+another to prevent "pumping" (too rapid activation and deactivation),
+another to smooth out the "knee" of the threshold curve, etc --- but
+what it really comes down to is: at what level should the signal be
+reduced, by how much, and what's the gain to make up for the overall
+loss in volume.
+
+One piece of advice: resist the temptation of overdoing this!
+Compression may make the sound punchier, but don't throw away all
+dynamics here or you'll risk draining the life from your hard-earned
+waveforms.  So I stick with a ratio of no more than two, keep the
+makeup gain fairly low, and the threshold somewhat high to only
+trigger the compressor in the upper fifth of the dynamic range.
+
+Next: equalization.  This is to scoop out an unpleasant character by
+attenuating certain frequency ranges.  Again, the Calf suite has got
+me covered.  A five band EQ is sufficient as I don't want to be
+tempted to make sharp cuts in the frequency spectrum of the signal.
+As a general rule I don't *boost* any frequencies but primarily *cut*.
+Here, too, the key is to be gentle.  Don't cut more than two or three
+decibels or you'll end up with a comically filtered sound.
+(Exceptions apply for drum recordings, but thankfully we dodged that
+bullet by using Hydrogen.)  If you find that you need to cut or boost
+more than that, chances are that there are problems with your
+recording.  Don't try to compensate for problems with post-processing
+that could have been avoided by improving the recording quality.  I
+scoop out the mids a tiny bit and cut out the *very* low bass
+frequencies that don't contribute anything more than a rumble.
+
+## MIDI Resurgence
+
+With the bass line and the drums in place it was time to revisit the
+harmonies for part B.  I really did want to record them with my very
+red virtual analog hardware synthesizer, but when I brought it into my
+tiny work room I realized that I had ran out of space on my lap --- I
+had run out of space on my desk months ago, and with all those audio
+cables piling up on the floor even that was no option.
+
+Lilypond generated a MIDI file earlier, so I sighed and told Ardour to
+import it.  I assigned the ancient electric piano plugin
+[mdaEPiano](https://guix.gnu.org/en/packages/lv2-mda-epiano-0.0.2/) as
+a synthesizer to the track, and expanded the track vertically to drag
+around every MIDI note event by hand, refining the notes and adding
+tiny timing and velocity imperfections to make it seem as if a human
+played them.  To paper over the clearly audible undesirable
+imperfections of the plugin's sound generation I added some Calf
+Reverb (for the graphics people: adding reverb is roughly equivalent
+to using the blur tool in a graphics application).
+
+MIDI support in Ardour is really well thought-out as you don't need to
+ever leave the main window, so you are always surrounded by audio
+context.  You just expand the track vertically and have as much access
+to the events as you want.  This approach may be a little unusual for
+those who are used to MIDI sequencers, but for my purposes it is close
+to perfect.
+
+## Lyrics and Vocals: Human vs Machine
+
+At this point things were coming together nicely, but we only had
+lyrics (and handful of words, really) for the chorus.  Not enough for
+a song, but just a little too much for a laundry list.  So I turned to
+IRC again where our resident Debian ambassador and assuredly human
+person Vagrant Cascadian happend to volunteer a stroke of genius: what
+if the lyrics were composed entirely of typos in package descriptions
+that had been fixed since the last release?  Vagrant carefully
+reordered the words to a poignant poem, bringing them alive as the
+voice of the adversarial machine, a symbol of the waning hold of the
+bugs and errors on our way to the next release.  What would be more
+fitting than to let the machine croak these words in the release song?
+
+I started up the Festival speech synthesis software and a few Scheme
+expressions later the inimitable monotone of none other than the
+entity known only as `cmu_us_fem_cg` droned the words into an audio
+file that I promptly imported into Ardour, and processed with the
+GxDetune plugin, Calf Vintage Delay, and some reverb.
+
+I did my best between bites of a Monday pre-release lunch to perform
+the role of the human contemplating this cycle of creation through
+hacking by recording three vocal lines (two low, one high) for the
+chorus.
+
+## Final touches
+
+With about half an hour or so left before the release announcement it
+became clear that there would be no "audio mastering" in the
+traditional sense.  I put on my monitoring headphones (flat frequency
+response for an "objective" mixing experience) and adjusted the volume
+levels, plugin settings, and faded in and out the noisy edges of each
+take.  I also added a few more effects: a phaser on the Chapman Stick
+track to emphasize that this is supposed to be funk; a crossover (Calf
+X-Over 2 Band) and three audio busses to first process the low bass
+frequencies separately from the high frequencies (e.g. to use
+different amplifier simulations) and then to rejoin them; and a
+limiter on the master bus to avoid any volume spikes above 0dB and to
+compress the mix.
+
+I exported the final mix as a Vorbis OGG audio file and sent it off to
+Ludovic to have it included in the release announcement.
+
+## Concluding thoughts
+
+So what's the verdict?  Is the result perfect?  Absolutely not!  But I
+do want to point out that any and all mistakes and imperfections are
+entirely due to my own lack of skill and time --- they are not the
+result of the limitations of free software.  A more skilled audio
+engineer would certainly not be limited by a system like the one I
+used, a system composed entirely of freedom-respecting software that
+is made extra reliable by the user-empowering and liberating features
+of Guix System.