Sonic Pi Vocoder Prototype

README.md

Prototype of vocoder on Sonic Pi

Demo here: https://www.dropbox.com/s/qiktze3ml7bz5iq/autotune_the_shipping_forecast.wav?dl=0 Original voice input here: https://soundcloud.com/jb_uk/neil-nunes-bbc-radio-4-and

This is a demo of a simple effects synth using the Vocoder.ar UGen from SuperCollider. This is a fairly primitive vocoder implementation made of a bunch of bandpass filters which are "tuned" to various frequencies.

The results are mixed, but it's difficult to get a decent reproduction of the words from this.

To get T-Pain/Imogen Heap style auto-tune it would be necessary to write a different algorithm probably using a technique called PSOLA which is described at the following links:

• https://valhalladsp.com/2009/05/21/auto-tune-autocorrelation-and-seismic-analysis/
• https://cnx.org/exports/22567958-1f9b-4426-8abe-b9e0736df034@1.1.pdf/auto-tune-1.1.pdf
• http://www.guitarpitchshifter.com/index.html

Part of the problem is that the algorithm is probably under copyright which makes distribution of an open source version more difficult.

sonic-pi-fx_vocoder.sc

//s.boot;
//s.quit;
(
SynthDef('sonic-pi-fx_vocoder', {
	arg out_bus=0, in_bus=0;
	var car, mod, result;
	car = In.ar(in_bus,1);
	mod = In.ar(in_bus+1,1);
	result = Vocoder.ar(car, mod, 32);

	Out.ar(out_bus, result.dup);
}).writeDefFile("/Users/xriley/Projects/sonic-pi/etc/synthdefs/compiled/"); // change this path to point to Sonic Pi on your system
)

vocoder_example.rb

live_loop :bd do
  sample :bd_haus
  sleep 0.5
end

in_thread do
  with_fx :vocoder do
    # right channel provides the voice input to the effect
    with_fx :band_eq, freq: 70, db: 2 do
      sample "/Users/xriley/Movies/shipping_forecast.wav", start: 0.506, amp: 5, rate: 1, pan: 1
    end
    
    # using a noisy synth gives more for the vocoder to work with
    x = synth :supersaw, sustain: 200, note_slide: 0.05, pan: -1
    200.times do
      control(x, note: (scale :a2, :minor_pentatonic, num_octaves: 2).choose)
      sleep [0.5,0.25,1].choose
    end
  end
end

vocoder_synthinfo.patch

diff --git a/app/server/ruby/lib/sonicpi/synths/synthinfo.rb b/app/server/ruby/lib/sonicpi/synths/synthinfo.rb
index d70c85199..135c8c765 100644
--- a/app/server/ruby/lib/sonicpi/synths/synthinfo.rb
+++ b/app/server/ruby/lib/sonicpi/synths/synthinfo.rb
@@ -4942,6 +4942,28 @@ A decent range of Q factors for naturally sounding boosts/cuts is 0.6 to 1.
       end
     end

+    class FXVocoder < FXInfo
+      def name
+        "Vocoder"
+      end
+
+      def introduced
+        Version.new(2,10,0)
+      end
+
+      def synth_name
+        "fx_vocoder"
+      end
+
+      def doc
+        ""
+      end
+
+      def arg_defaults
+        super.merge({})
+      end
+    end
+
     class FXMono < FXInfo
       def name
         "Mono"
@@ -7606,6 +7628,7 @@ Use FX `:band_eq` with a negative db for the opposite effect - to attenuate a gi
         :fx_replace_reverb => FXReverb.new,
         :fx_level => FXLevel.new,
         :fx_mono => FXMono.new,
+        :fx_vocoder => FXVocoder.new,
         :fx_replace_level => FXLevel.new,
         :fx_echo => FXEcho.new,
         :fx_replace_echo => FXEcho.new,

This might be worth looking at for a PSOLA implementation

Work on this is continuing - updates here https://in-thread.sonic-pi.net/t/prototype-of-a-vocoder-in-sonic-pi/1247/4