SuperCollider Synthdefs that can play chords

gordonguthrie · January 4, 2023, 12:58pm

I can play chords with Sonic Pi synths:

use_synth :dsaw

play 60

play(note: chord(:c3, :major))

No problem. When I write my own ones though they play single notes fine, then they crash when I play chords:

use_synth(:mysecondsynth)

play 60

play(note: chord(:c3, :major))

The error is:

Thread death!
Unable to normalise argument with key note: and value (ring <SonicPi::Chord...

So I am learning SuperCollider and figure this must be my problem and look at passing arrays as parameters and stuff. Nothing I try works. Then I read the source code to SuperCollider synths in github and they all seem to be single note synths.

I took the source of sonic-pi-rodeo renamed it an ran it and it did indeed fail with the same error on a chord.

Is there an example of how to write a SuperCollider synth that accepts chords as well as notes for me to look at?

emlyn · January 4, 2023, 5:02pm

I’m not sure about the answer to your question, but in the meantime, you can always use a workaround to play each note separately:

use_synth(:mysecondsynth)

chord(:c3, :major).each do |note|
  play note
end

gordonguthrie · January 4, 2023, 7:37pm

yeah, but if the plan is to get more synths bundled with Sonic Pi using Supercollider that’s not really sustainable and if you are trying to do more complex synthesis then not having all the notes available in your SynthDef might be limiting, perhaps?

gordonguthrie · March 11, 2023, 4:11pm

So it would appear that the issue is the munging of notes in the heart of Sonic Pi

github.com

sonic-pi-net/sonic-pi/blob/dev/app/server/ruby/lib/sonicpi/lang/sound.rb#L1090


      
          
          
args_h = tls.merge(args_h).to_h
          
          
if rest? args_h
            unless __thread_locals.get(:sonic_pi_mod_sound_synth_silent)
              __delayed_message "synth #{synth_name.to_sym.inspect}, {note: :rest}"
            end
            return BlankNode.new(args_h)
          end
          
          
if info
            # only munge around with :note and notes if
            # this is a built-in synth.
            notes = args_h[:notes] || args_h[:note]
            if is_list_like?(notes)
              args_h.delete(:notes)
              args_h.delete(:note)
              shifted_notes = notes.map {|n| normalise_transpose_and_tune_note_from_args(n, args_h)}
              return trigger_chord(synth_name, shifted_notes, args_h)
            end

I have been adding synths by loading them with load_synthdefs - I might need to actually compile them in to get them to play chords

Is that right @ethancrawford @samaaron ?

samaaron · March 11, 2023, 7:51pm

Hi @gordonguthrie,

by default, Sonic Pi doesn’t mess around with any args for synths that aren’t built-in. This is because it’s impossible to know whether an arg which shares the same name, such as :note is accidental or not. If it’s accidental, it might be that the arg has completely different semantics to that of Sonic Pi’s built-in synths.

For Sonic Pi’s built-in synths there is metadata describing each of the args - their names, docs and some checker functions (checking bounds etc.). This is unfortunately not something we’ve yet worked on making easy to extend for user-defined synths.

The built-in synth metadata is stored in the synthinfo.rb files. For example, here’s a link to the :square synth:

github.com

sonic-pi-net/sonic-pi/blob/dev/app/server/ruby/lib/sonicpi/synths/synthinfo.rb#L864


      
              super.merge({
                cutoff: 100,
                cutoff_slide: 0,
                cutoff_slide_shape: 1,
                cutoff_slide_curve: 0
              })
            end
          end
          
          

          
class Square < SonicPiSynth
            def name
              "Square Wave"
            end
          
          
  def introduced
              Version.new(2,2,0)
            end
          
          
  def synth_name
              "square"

It should be possible to hack and extend this file with metadata for your synth. However, we really should look at ways for people to bundle similar metadata with their own synths. I’m thinking a toml file or similar would be sensible for such a thing.

gordonguthrie · March 11, 2023, 8:28pm

That makes sense.

I am slowly writing a manual for writing SuperCollider synths with SonicPi, as and when I get a dev enivronment up I will have a look at it…

samaaron · March 11, 2023, 8:32pm

This is fab, thanks so much for working on this - it will be a really valuable resource.

gordonguthrie · March 11, 2023, 11:29pm

I am using my literate code reader so I can just write well-commented SuperCollider code and it will generate the manual pages automatically from the source

I don’t know anything unless I write it down, and I can’t remember anything from one day to the next so I might as well document my own learning SuperCollider as I go along