Add Psytrance Visualizer macOS app with Metal rendering

A complete audio-reactive visualizer for psytrance music featuring:

Audio Analysis (DSPEngine):
- FFT spectrum analysis via Accelerate/vDSP
- 64-band Mel spectrogram
- Sub-bass energy extraction (<100Hz)
- Automatic sidechain pump detection
- Harmonic-to-Noise ratio (HNR) calculation
- Peak/transient detection

8 Visualization Modes (Metal Shaders):
1. FFT Classic - Frequency spectrum bars with glow
2. Mel Spectrogram - Waterfall display
3. Sub-Bass - Pulsating rings
4. Sidechain Pump - Breathing zoom effect
5. Harmonic/Noise - Geometric vs chaotic particles
6. Mandelbrot - Audio-reactive fractal zoom
7. Tunnel Warp - Infinite tunnel with distortion
8. DMT Geometry - Sacred geometry patterns

Features:
- Selectable audio input device (BlackHole support)
- Configurable buffer size (512/1024)
- Reactivity slider for visual intensity
- Auto-hiding control panel
- Fullscreen support with keyboard shortcuts (1-8, F, ESC)
- Persistent settings via UserDefaults
- Psytrance-inspired neon/UV color palette

PsytranceVisualizer/Models/AppSettings.swift

@@ -0,0 +1,90 @@
+//
+//  AppSettings.swift
+//  PsytranceVisualizer
+//
+//  Persistent application settings
+//
+
+import Foundation
+
+/// Application settings that are persisted between sessions
+struct AppSettings: Codable {
+    /// Selected audio input device UID
+    var selectedAudioDeviceUID: String?
+
+    /// Audio buffer size (512 or 1024 samples)
+    var bufferSize: Int
+
+    /// Last used visualization mode (1-8)
+    var lastVisualizationMode: Int
+
+    /// Reactivity slider value (0.0 - 1.0)
+    var reactivity: Float
+
+    /// Whether app was in fullscreen mode
+    var isFullscreen: Bool
+
+    /// Last window frame (for restoration)
+    var windowFrame: CodableRect?
+
+    /// Volume/gain adjustment
+    var inputGain: Float
+
+    /// Whether to show FPS counter
+    var showFPS: Bool
+
+    /// Default settings
+    static var `default`: AppSettings {
+        AppSettings(
+            selectedAudioDeviceUID: nil,
+            bufferSize: 1024,
+            lastVisualizationMode: 1,
+            reactivity: 0.5,
+            isFullscreen: false,
+            windowFrame: nil,
+            inputGain: 1.0,
+            showFPS: false
+        )
+    }
+
+    /// Available buffer sizes
+    static let availableBufferSizes = [512, 1024]
+
+    /// Validates and clamps settings to valid ranges
+    mutating func validate() {
+        // Clamp buffer size to valid options
+        if !AppSettings.availableBufferSizes.contains(bufferSize) {
+            bufferSize = 1024
+        }
+
+        // Clamp visualization mode
+        if lastVisualizationMode < 1 || lastVisualizationMode > 8 {
+            lastVisualizationMode = 1
+        }
+
+        // Clamp reactivity
+        reactivity = max(0.0, min(1.0, reactivity))
+
+        // Clamp input gain
+        inputGain = max(0.0, min(2.0, inputGain))
+    }
+}
+
+/// Codable wrapper for CGRect
+struct CodableRect: Codable {
+    var x: Double
+    var y: Double
+    var width: Double
+    var height: Double
+
+    init(from rect: CGRect) {
+        self.x = Double(rect.origin.x)
+        self.y = Double(rect.origin.y)
+        self.width = Double(rect.size.width)
+        self.height = Double(rect.size.height)
+    }
+
+    var cgRect: CGRect {
+        CGRect(x: x, y: y, width: width, height: height)
+    }
+}

PsytranceVisualizer/Models/AudioAnalysisData.swift

@@ -0,0 +1,111 @@
+//
+//  AudioAnalysisData.swift
+//  PsytranceVisualizer
+//
+//  Audio analysis data structure containing all DSP results
+//
+
+import Foundation
+
+/// Contains all audio analysis data computed by DSPEngine
+struct AudioAnalysisData {
+    // MARK: - FFT Data
+
+    /// Raw FFT magnitude spectrum
+    var fftMagnitudes: [Float]
+
+    // MARK: - Mel Spectrogram
+
+    /// 64 Mel frequency bands
+    var melBands: [Float]
+
+    // MARK: - Sub-Bass Analysis
+
+    /// RMS energy below 100Hz (0.0 - 1.0)
+    var subBassEnergy: Float
+
+    /// History buffer for time-based visualization
+    var subBassHistory: [Float]
+
+    // MARK: - Sidechain Detection
+
+    /// Current envelope follower value (0.0 - 1.0)
+    var sidechainEnvelope: Float
+
+    /// Detected pumping amount (0.0 - 1.0)
+    var sidechainPumpAmount: Float
+
+    /// Whether pump is currently active
+    var isPumping: Bool
+
+    // MARK: - Harmonic-to-Noise Ratio
+
+    /// HNR ratio (0.0 = noise, 1.0 = pure harmonic)
+    var hnrRatio: Float
+
+    // MARK: - Transient Detection
+
+    /// Whether a transient peak was detected
+    var isPeak: Bool
+
+    /// Intensity of the detected peak (0.0 - 1.0)
+    var peakIntensity: Float
+
+    // MARK: - Stereo Channels
+
+    /// Left channel samples
+    var leftChannel: [Float]
+
+    /// Right channel samples
+    var rightChannel: [Float]
+
+    // MARK: - Additional Analysis
+
+    /// Spectral centroid (brightness) normalized 0.0 - 1.0
+    var spectralCentroid: Float
+
+    /// Overall RMS level
+    var rmsLevel: Float
+
+    // MARK: - Initialization
+
+    /// Creates an empty AudioAnalysisData with default values
+    static var empty: AudioAnalysisData {
+        AudioAnalysisData(
+            fftMagnitudes: [],
+            melBands: Array(repeating: 0, count: 64),
+            subBassEnergy: 0,
+            subBassHistory: [],
+            sidechainEnvelope: 0,
+            sidechainPumpAmount: 0,
+            isPumping: false,
+            hnrRatio: 0.5,
+            isPeak: false,
+            peakIntensity: 0,
+            leftChannel: [],
+            rightChannel: [],
+            spectralCentroid: 0.5,
+            rmsLevel: 0
+        )
+    }
+
+    /// Creates AudioAnalysisData with specified FFT size
+    static func create(fftSize: Int) -> AudioAnalysisData {
+        AudioAnalysisData(
+            fftMagnitudes: Array(repeating: 0, count: fftSize / 2),
+            melBands: Array(repeating: 0, count: 64),
+            subBassEnergy: 0,
+            subBassHistory: Array(repeating: 0, count: 128),
+            sidechainEnvelope: 0,
+            sidechainPumpAmount: 0,
+            isPumping: false,
+            hnrRatio: 0.5,
+            isPeak: false,
+            peakIntensity: 0,
+            leftChannel: [],
+            rightChannel: [],
+            spectralCentroid: 0.5,
+            rmsLevel: 0
+        )
+    }
+}

PsytranceVisualizer/Models/VisualizationMode.swift

@@ -0,0 +1,109 @@
+//
+//  VisualizationMode.swift
+//  PsytranceVisualizer
+//
+//  Enumeration of all available visualization modes
+//
+
+import Foundation
+
+/// Available visualization modes, accessible via keyboard shortcuts 1-8
+enum VisualizationMode: Int, CaseIterable, Codable {
+    case fftClassic = 1
+    case melSpectrogram = 2
+    case subBass = 3
+    case sidechainPump = 4
+    case hnr = 5
+    case mandelbrot = 6
+    case tunnelWarp = 7
+    case dmtGeometry = 8
+
+    /// Display name for UI
+    var displayName: String {
+        switch self {
+        case .fftClassic:
+            return "FFT Classic"
+        case .melSpectrogram:
+            return "Mel Spektrogramm"
+        case .subBass:
+            return "Sub-Bass (<100Hz)"
+        case .sidechainPump:
+            return "Sidechain Pump"
+        case .hnr:
+            return "Harmonic/Noise"
+        case .mandelbrot:
+            return "Mandelbrot"
+        case .tunnelWarp:
+            return "Tunnel Warp"
+        case .dmtGeometry:
+            return "DMT Geometry"
+        }
+    }
+
+    /// Keyboard shortcut (1-8)
+    var shortcut: String {
+        return "\(self.rawValue)"
+    }
+
+    /// Metal shader function name
+    var shaderFunctionName: String {
+        switch self {
+        case .fftClassic:
+            return "fftClassicFragment"
+        case .melSpectrogram:
+            return "melSpectrogramFragment"
+        case .subBass:
+            return "subBassFragment"
+        case .sidechainPump:
+            return "sidechainPumpFragment"
+        case .hnr:
+            return "hnrFragment"
+        case .mandelbrot:
+            return "mandelbrotFragment"
+        case .tunnelWarp:
+            return "tunnelWarpFragment"
+        case .dmtGeometry:
+            return "dmtGeometryFragment"
+        }
+    }
+
+    /// Description of the visualization
+    var description: String {
+        switch self {
+        case .fftClassic:
+            return "Classic frequency spectrum bars with glow effects"
+        case .melSpectrogram:
+            return "64-band Mel spectrogram with scrolling waterfall display"
+        case .subBass:
+            return "Pulsating rings visualizing sub-bass energy below 100Hz"
+        case .sidechainPump:
+            return "Breathing zoom effect synchronized to sidechain pumping"
+        case .hnr:
+            return "Harmonic vs noise visualization with geometric shapes"
+        case .mandelbrot:
+            return "Audio-reactive Mandelbrot fractal with zoom and color cycling"
+        case .tunnelWarp:
+            return "Infinite tunnel effect with warp distortion"
+        case .dmtGeometry:
+            return "Sacred geometry patterns: Flower of Life, Metatron's Cube, Sri Yantra"
+        }
+    }
+
+    /// Creates mode from keyboard key code
+    static func fromKeyCode(_ keyCode: UInt16) -> VisualizationMode? {
+        // Key codes for 1-8 on US keyboard
+        let keyCodes: [UInt16: Int] = [
+            18: 1,  // 1
+            19: 2,  // 2
+            20: 3,  // 3
+            21: 4,  // 4
+            23: 5,  // 5
+            22: 6,  // 6
+            26: 7,  // 7
+            28: 8   // 8
+        ]
+
+        guard let modeNumber = keyCodes[keyCode] else { return nil }
+        return VisualizationMode(rawValue: modeNumber)
+    }
+}