DripSynth

DripSynth is a physical modeling synthesizer for the Daisy Patch SM. It uses the Drip physical modeling voice to create percussive, water-like sounds, which are then processed through a filter and a chain of effects.

Features

• Voice: Drip physical modeling voice.
• Filter: State-Variable Filter (SVF) with low-pass output.
• Envelope: ADSR envelope to shape the sound.
• Effects:
  • Wavefolder
  • Pitch Shifter

Controls

Control	Parameter	Description
GATE IN 1	Trigger	Triggers the Drip voice and the ADSR envelope.
CV 1	ADSR Attack	Sets the attack time of the envelope (0.001s to 4s).
CV 2	ADSR Decay	Sets the decay time of the envelope (0.001s to 4s).
CV 3	ADSR Sustain	Sets the sustain level of the envelope (0-1).
CV 4	ADSR Release	Sets the release time of the envelope (0.001s to 4s).
CV 5	Filter Cutoff	Sets the cutoff frequency of the SVF filter (20Hz-20kHz).
CV 6	Filter Resonance	Sets the resonance of the SVF filter (0-0.95).
CV 7	Wavefolder Gain	Controls the amount of wavefolding (0-10).
CV 8	Wavefolder Offset	Sets the offset of the wavefolder (-0.8 to 0.8).
KNOB 1	Pitch Shifter Transpose	Transposes the pitch of the sound (-12 to +12 semitones).
KNOB 2	Pitch Shifter Fun	Controls the "fun" parameter of the pitch shifter (0-1).

Signal Flow

---
title: A Physical Modeling Synth to make Drip sounds for daisy patch
config:
  theme: default
---
graph TD
   subgraph Drip [DripSynth Physical Modeling Voice]
       subgraph Dripin [Ocsillator]
         insig(Trigger)
      end
     subgraph ADSR [ADSR Envelope]
         Attack(Attack ADSR)
         Decay(Decay ADSR)
         Sustain(Sustain ADSR)
         Release(Release ADSR)
      end
      subgraph SVF [SVF Filter]
         Cutoff(Cutoff SVF)
         Resonance(Resonance SVF)
      end
      subgraph Wavefolder
         gain(Wavefolder Gain)
         offset(Wavefolder Offset)
      end
      subgraph PitchShifter
         transpose(Pitchshifter Transpose)
         fun(Pitchshifter Fun)
      end
   end

    subgraph SM [Daisy Patch SM]
        GATE_IN_1[GATE IN 1]
        CV_1(CV 1)
        CV_2(CV 2)
        CV_3(CV 3)
        CV_4(CV 4)
        CV_5(CV 5)
        CV_6(CV 6)
        CV_7(CV 7)
        CV_8(CV 8)
        ADC_9(KNOB 1)
        ADC_10(KNOB 2)
        AUDIO_OUT_L[AUDIO OUT L]
        AUDIO_OUT_R[AUDIO OUT R]
    end



    GATE_IN_1 -->|trig in| Dripin;
    GATE_IN_1 -->|trig in| ADSR;



    CV_1 --> Attack;
    CV_2 --> Decay;
    CV_3 --> Sustain;
    CV_4 --> Release;

    CV_5 --> Cutoff;
    CV_6 --> Resonance;

    CV_7 --> gain;
    CV_8 --> offset;

    ADC_9 --> transpose;
    ADC_10 --> fun;

    Dripin -->|signal to filter| SVF;
    ADSR --> Dripin;
    SVF --> Wavefolder;
    Wavefolder --> PitchShifter;
    PitchShifter --> AUDIO_OUT_L;
    PitchShifter --> AUDIO_OUT_R;

Loading

Building and Uploading

To build and upload the DripSynth to your Daisy Patch SM, follow these steps:

1. Navigate to the patch_sm/DripSynth directory:

   cd patch_sm/DripSynth

2. Build the project:

   make

3. Upload the program to the Daisy Patch SM:

   make program-dfu

Trigger/Gate Input

The GATE IN 1 input is designed to accept standard Eurorack-level trigger or gate signals.

• Signal Type: It works with both short triggers and longer gates.
  • A trigger will fire the sound once.
  • A gate will fire the sound and hold the envelope open until the gate goes low.
• Voltage Level: The input expects a voltage of approximately +5V or higher to register as a high signal.
• Audio as Trigger: Using an audio signal as a trigger is not recommended. It will cause the sound to re-trigger at audio rates, resulting in a noisy, unpredictable output.

Audio Output

The audio output is sent to the AUDIO_OUT_L and AUDIO_OUT_R jacks on the Daisy Patch SM, which correspond to pins B2 and B1 respectively. No additional code is required to enable the audio output.

Unit Testing

While not included in this project, here are some suggestions for unit tests that would be appropriate for the DripSynth:

• Module-Level Tests:

  • Drip Voice:
    • Verify that Process(true) produces a sound with the expected characteristics (e.g., a decaying sine-like waveform).
    • Confirm that Process(false) after a trigger results in a decaying sound that eventually becomes silent.
  • ADSR Envelope:
    • Test that the envelope generator correctly follows the Attack, Decay, Sustain, and Release phases.
    • Ensure that the output values are always within the expected 0.0 to 1.0 range.
  • SVF Filter:
    • Verify that the low-pass output correctly attenuates frequencies above the cutoff frequency.
    • Test that the resonance control behaves as expected, creating a peak at the cutoff frequency.

• Integration Tests:

  • Test the entire audio signal chain by providing a trigger signal and analyzing the output to ensure it has the expected characteristics.
  • Verify the control mappings by setting mock ADC values and checking that the corresponding parameters in the DSP modules are updated correctly.

Appendix: Control Scaling Philosophy

The raw 0.0 to 1.0 output of a CV input or knob is rarely the most musically expressive range for a parameter. To make the DripSynth more playable and intuitive, the control ranges have been carefully scaled.

• ADSR Times (Attack, Decay, Release): A linear 0-1 second range is not ideal. For percussive sounds, very short envelope times are needed, while ambient sounds require much longer times. By mapping the input to a range of 0.001 to 4 seconds, the DripSynth can produce both snappy, clicky envelopes and long, evolving soundscapes.

• Filter Resonance: The Svf filter can self-oscillate loudly and harshly when the resonance is set to 1.0. To prevent sudden, unpleasant volume spikes and make the resonance more controllable, the maximum value has been capped at 0.95. This keeps the filter's behavior in a more musical "sweet spot".

• Wavefolder Offset: The offset parameter shifts the waveform before it enters the wavefolder, which alters the harmonic content of the resulting sound. A bipolar range is more useful here, as it allows for a wider variety of timbres. The input is mapped to a -0.8 to +0.8 range, providing a more diverse sonic palette.

• Pitch Shifter Transposition: The ability to pitch a sound both up and down is essential for musical applications. The original 0 to +24 semitone range has been changed to -12 to +12 semitones, allowing for one octave of pitch shifting in either direction.