sfx-maker: sfxc - sfxr-style .sfx text presets -> 16-bit WAV synthesis

- waves: square (duty), saw, sine, triangle, pitched noise (seeded, deterministic)
- envelope attack/sustain/decay, freq slide, vibrato, arpeggio jump,
  one-pole low/high-pass filters, clamped output
- presets blip/coin/explosion/hurt/jump/laser/powerup with seeded variants;
  preset writes editable .sfx or renders .wav directly
- go tests: parse/validate, determinism, per-preset RMS, WAV header roundtrip

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmdG9GqfSWCzts7AkDwRDh

sfx-maker/sfx/presets.go

@@ -0,0 +1,114 @@
+package sfx
+
+import (
+	"fmt"
+	"math/rand"
+	"sort"
+)
+
+// Preset returns ready-made parameters for classic game sounds.
+// seed 0 gives the canonical version; other seeds vary it slightly so
+// agents can generate alternatives ("give me three coin variants").
+func Preset(name string, seed int64) (*Params, error) {
+	p := Defaults()
+	p.Name = name
+	switch name {
+	case "jump":
+		p.Wave = "square"
+		p.Duty = 0.5
+		p.Freq = 330
+		p.FreqSlide = 900
+		p.Attack = 0.01
+		p.Sustain = 0.08
+		p.Decay = 0.18
+	case "coin":
+		p.Wave = "square"
+		p.Duty = 0.5
+		p.Freq = 988
+		p.ArpFactor = 1.335 // up a fourth: B5 -> E6
+		p.ArpTime = 0.06
+		p.Attack = 0.005
+		p.Sustain = 0.08
+		p.Decay = 0.25
+	case "laser":
+		p.Wave = "saw"
+		p.Freq = 1400
+		p.FreqSlide = -6000
+		p.Attack = 0.005
+		p.Sustain = 0.05
+		p.Decay = 0.12
+		p.HighPass = 300
+	case "explosion":
+		p.Wave = "noise"
+		p.Freq = 900
+		p.FreqSlide = -600
+		p.Attack = 0.01
+		p.Sustain = 0.15
+		p.Decay = 0.55
+		p.LowPass = 2200
+	case "hurt":
+		p.Wave = "saw"
+		p.Freq = 300
+		p.FreqSlide = -700
+		p.Attack = 0.005
+		p.Sustain = 0.04
+		p.Decay = 0.14
+	case "powerup":
+		p.Wave = "square"
+		p.Duty = 0.4
+		p.Freq = 220
+		p.FreqSlide = 700
+		p.VibratoDepth = 25
+		p.VibratoRate = 9
+		p.Attack = 0.01
+		p.Sustain = 0.25
+		p.Decay = 0.25
+	case "blip":
+		p.Wave = "square"
+		p.Duty = 0.4
+		p.Freq = 660
+		p.Attack = 0.002
+		p.Sustain = 0.03
+		p.Decay = 0.05
+	default:
+		return nil, fmt.Errorf("unknown preset %q (available: %s)", name, PresetNames())
+	}
+	if seed != 0 {
+		vary(&p, seed)
+	}
+	if err := p.Validate(); err != nil {
+		return nil, fmt.Errorf("preset %s (seed %d): %w", name, seed, err)
+	}
+	return &p, nil
+}
+
+// vary nudges the tonal parameters deterministically from the seed.
+func vary(p *Params, seed int64) {
+	rng := rand.New(rand.NewSource(seed))
+	jitter := func(v, amount float64) float64 {
+		return v * (1 + amount*(rng.Float64()*2-1))
+	}
+	p.Freq = jitter(p.Freq, 0.15)
+	p.FreqSlide = jitter(p.FreqSlide, 0.25)
+	p.Sustain = jitter(p.Sustain, 0.2)
+	p.Decay = jitter(p.Decay, 0.2)
+	if p.ArpFactor != 0 {
+		p.ArpFactor = jitter(p.ArpFactor, 0.05)
+	}
+	p.Seed = seed // noise variation too
+}
+
+var presetNames = []string{"blip", "coin", "explosion", "hurt", "jump", "laser", "powerup"}
+
+// PresetNames lists the available presets, sorted.
+func PresetNames() string {
+	sort.Strings(presetNames)
+	out := ""
+	for i, n := range presetNames {
+		if i > 0 {
+			out += ", "
+		}
+		out += n
+	}
+	return out
+}