Update project.pbxproj

.gitignore

@@ -0,0 +1 @@
+/build

LidAngleSensor.xcodeproj/project.pbxproj

@@ -268,7 +268,7 @@
 					"@executable_path/../Frameworks",
 				);
 				MACOSX_DEPLOYMENT_TARGET = 11.5;
-				MARKETING_VERSION = 1.0;
+				MARKETING_VERSION = 1.0.3;
 				PRODUCT_BUNDLE_IDENTIFIER = gold.samhenri.LidAngleSensor;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				REGISTER_APP_GROUPS = YES;
@@ -310,7 +310,7 @@
 					"@executable_path/../Frameworks",
 				);
 				MACOSX_DEPLOYMENT_TARGET = 11.5;
-				MARKETING_VERSION = 1.0;
+				MARKETING_VERSION = 1.0.3;
 				PRODUCT_BUNDLE_IDENTIFIER = gold.samhenri.LidAngleSensor;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				REGISTER_APP_GROUPS = YES;

LidAngleSensor/AppDelegate.m

@@ -8,32 +8,44 @@
 #import "AppDelegate.h"
 #import "LidAngleSensor.h"
 #import "CreakAudioEngine.h"
+#import "ThereminAudioEngine.h"
 #import "NSLabel.h"
 
+typedef NS_ENUM(NSInteger, AudioMode) {
+    AudioModeCreak,
+    AudioModeTheremin
+};
+
 @interface AppDelegate ()
 @property (strong, nonatomic) LidAngleSensor *lidSensor;
-@property (strong, nonatomic) CreakAudioEngine *audioEngine;
+@property (strong, nonatomic) CreakAudioEngine *creakAudioEngine;
+@property (strong, nonatomic) ThereminAudioEngine *thereminAudioEngine;
 @property (strong, nonatomic) NSLabel *angleLabel;
 @property (strong, nonatomic) NSLabel *statusLabel;
 @property (strong, nonatomic) NSLabel *velocityLabel;
 @property (strong, nonatomic) NSLabel *audioStatusLabel;
 @property (strong, nonatomic) NSButton *audioToggleButton;
+@property (strong, nonatomic) NSSegmentedControl *modeSelector;
+@property (strong, nonatomic) NSLabel *modeLabel;
 @property (strong, nonatomic) NSTimer *updateTimer;
+@property (nonatomic, assign) AudioMode currentAudioMode;
 @end
 
 @implementation AppDelegate
 
 - (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
+    self.currentAudioMode = AudioModeCreak; // Default to creak mode
     [self createWindow];
     [self initializeLidSensor];
-    [self initializeAudioEngine];
+    [self initializeAudioEngines];
     [self startUpdatingDisplay];
 }
 
 - (void)applicationWillTerminate:(NSNotification *)aNotification {
     [self.updateTimer invalidate];
     [self.lidSensor stopLidAngleUpdates];
-    [self.audioEngine stopEngine];
+    [self.creakAudioEngine stopEngine];
+    [self.thereminAudioEngine stopEngine];
 }
 
 - (BOOL)applicationSupportsSecureRestorableState:(NSApplication *)app {
@@ -41,8 +53,8 @@
 }
 
 - (void)createWindow {
-    // Create the main window (taller to accommodate audio controls)
-    NSRect windowFrame = NSMakeRect(100, 100, 450, 420);
+    // Create the main window (taller to accommodate mode selection and audio controls)
+    NSRect windowFrame = NSMakeRect(100, 100, 450, 480);
     self.window = [[NSWindow alloc] initWithContentRect:windowFrame
                                               styleMask:NSWindowStyleMaskTitled | 
                                                        NSWindowStyleMaskClosable | 
@@ -98,6 +110,25 @@
     [self.audioStatusLabel setTextColor:[NSColor secondaryLabelColor]];
     [contentView addSubview:self.audioStatusLabel];
     
+    // Create mode label
+    self.modeLabel = [[NSLabel alloc] init];
+    [self.modeLabel setStringValue:@"Audio Mode:"];
+    [self.modeLabel setFont:[NSFont systemFontOfSize:14 weight:NSFontWeightMedium]];
+    [self.modeLabel setAlignment:NSTextAlignmentCenter];
+    [self.modeLabel setTextColor:[NSColor labelColor]];
+    [contentView addSubview:self.modeLabel];
+    
+    // Create mode selector
+    self.modeSelector = [[NSSegmentedControl alloc] init];
+    [self.modeSelector setSegmentCount:2];
+    [self.modeSelector setLabel:@"Creak" forSegment:0];
+    [self.modeSelector setLabel:@"Theremin" forSegment:1];
+    [self.modeSelector setSelectedSegment:0]; // Default to creak
+    [self.modeSelector setTarget:self];
+    [self.modeSelector setAction:@selector(modeChanged:)];
+    [self.modeSelector setTranslatesAutoresizingMaskIntoConstraints:NO];
+    [contentView addSubview:self.modeSelector];
+    
     // Set up auto layout constraints
     [NSLayoutConstraint activateConstraints:@[
         // Angle label (main display, now at top)
@@ -125,7 +156,18 @@
         [self.audioStatusLabel.topAnchor constraintEqualToAnchor:self.audioToggleButton.bottomAnchor constant:15],
         [self.audioStatusLabel.centerXAnchor constraintEqualToAnchor:contentView.centerXAnchor],
         [self.audioStatusLabel.widthAnchor constraintLessThanOrEqualToAnchor:contentView.widthAnchor constant:-40],
-        [self.audioStatusLabel.bottomAnchor constraintLessThanOrEqualToAnchor:contentView.bottomAnchor constant:-20]
+        
+        // Mode label
+        [self.modeLabel.topAnchor constraintEqualToAnchor:self.audioStatusLabel.bottomAnchor constant:25],
+        [self.modeLabel.centerXAnchor constraintEqualToAnchor:contentView.centerXAnchor],
+        [self.modeLabel.widthAnchor constraintLessThanOrEqualToAnchor:contentView.widthAnchor constant:-40],
+        
+        // Mode selector
+        [self.modeSelector.topAnchor constraintEqualToAnchor:self.modeLabel.bottomAnchor constant:10],
+        [self.modeSelector.centerXAnchor constraintEqualToAnchor:contentView.centerXAnchor],
+        [self.modeSelector.widthAnchor constraintEqualToConstant:200],
+        [self.modeSelector.heightAnchor constraintEqualToConstant:28],
+        [self.modeSelector.bottomAnchor constraintLessThanOrEqualToAnchor:contentView.bottomAnchor constant:-20]
     ]];
 }
 
@@ -143,10 +185,11 @@
     }
 }
 
-- (void)initializeAudioEngine {
-    self.audioEngine = [[CreakAudioEngine alloc] init];
+- (void)initializeAudioEngines {
+    self.creakAudioEngine = [[CreakAudioEngine alloc] init];
+    self.thereminAudioEngine = [[ThereminAudioEngine alloc] init];
     
-    if (self.audioEngine) {
+    if (self.creakAudioEngine && self.thereminAudioEngine) {
         [self.audioStatusLabel setStringValue:@""];
     } else {
         [self.audioStatusLabel setStringValue:@"Audio initialization failed"];
@@ -156,21 +199,59 @@
 }
 
 - (IBAction)toggleAudio:(id)sender {
-    if (!self.audioEngine) {
+    id currentEngine = [self currentAudioEngine];
+    if (!currentEngine) {
         return;
     }
     
-    if (self.audioEngine.isEngineRunning) {
-        [self.audioEngine stopEngine];
+    if ([currentEngine isEngineRunning]) {
+        [currentEngine stopEngine];
         [self.audioToggleButton setTitle:@"Start Audio"];
         [self.audioStatusLabel setStringValue:@""];
     } else {
-        [self.audioEngine startEngine];
+        [currentEngine startEngine];
         [self.audioToggleButton setTitle:@"Stop Audio"];
         [self.audioStatusLabel setStringValue:@""];
     }
 }
 
+- (IBAction)modeChanged:(id)sender {
+    NSSegmentedControl *control = (NSSegmentedControl *)sender;
+    AudioMode newMode = (AudioMode)control.selectedSegment;
+    
+    // Stop current engine if running
+    id currentEngine = [self currentAudioEngine];
+    BOOL wasRunning = [currentEngine isEngineRunning];
+    if (wasRunning) {
+        [currentEngine stopEngine];
+    }
+    
+    // Update mode
+    self.currentAudioMode = newMode;
+    
+    // Start new engine if the previous one was running
+    if (wasRunning) {
+        id newEngine = [self currentAudioEngine];
+        [newEngine startEngine];
+        [self.audioToggleButton setTitle:@"Stop Audio"];
+    } else {
+        [self.audioToggleButton setTitle:@"Start Audio"];
+    }
+    
+    [self.audioStatusLabel setStringValue:@""];
+}
+
+- (id)currentAudioEngine {
+    switch (self.currentAudioMode) {
+        case AudioModeCreak:
+            return self.creakAudioEngine;
+        case AudioModeTheremin:
+            return self.thereminAudioEngine;
+        default:
+            return self.creakAudioEngine;
+    }
+}
+
 - (void)startUpdatingDisplay {
     // Update every 16ms (60Hz) for smooth real-time audio and display updates
     self.updateTimer = [NSTimer scheduledTimerWithTimeInterval:0.016
@@ -196,12 +277,13 @@
         [self.angleLabel setStringValue:[NSString stringWithFormat:@"%.1f°", angle]];
         [self.angleLabel setTextColor:[NSColor systemBlueColor]];
         
-        // Update audio engine with new angle
-        if (self.audioEngine) {
-            [self.audioEngine updateWithLidAngle:angle];
+        // Update current audio engine with new angle
+        id currentEngine = [self currentAudioEngine];
+        if (currentEngine) {
+            [currentEngine updateWithLidAngle:angle];
             
             // Update velocity display with leading zero and whole numbers
-            double velocity = self.audioEngine.currentVelocity;
+            double velocity = [currentEngine currentVelocity];
             int roundedVelocity = (int)round(velocity);
             if (roundedVelocity < 100) {
                 [self.velocityLabel setStringValue:[NSString stringWithFormat:@"Velocity: %02d deg/s", roundedVelocity]];
@@ -209,13 +291,17 @@
                 [self.velocityLabel setStringValue:[NSString stringWithFormat:@"Velocity: %d deg/s", roundedVelocity]];
             }
             
-            // Keep velocity label color consistent
-            
             // Show audio parameters when running
-            if (self.audioEngine.isEngineRunning) {
-                double gain = self.audioEngine.currentGain;
-                double rate = self.audioEngine.currentRate;
-                [self.audioStatusLabel setStringValue:[NSString stringWithFormat:@"Gain: %.2f, Rate: %.2f", gain, rate]];
+            if ([currentEngine isEngineRunning]) {
+                if (self.currentAudioMode == AudioModeCreak) {
+                    double gain = [currentEngine currentGain];
+                    double rate = [currentEngine currentRate];
+                    [self.audioStatusLabel setStringValue:[NSString stringWithFormat:@"Gain: %.2f, Rate: %.2f", gain, rate]];
+                } else if (self.currentAudioMode == AudioModeTheremin) {
+                    double frequency = [currentEngine currentFrequency];
+                    double volume = [currentEngine currentVolume];
+                    [self.audioStatusLabel setStringValue:[NSString stringWithFormat:@"Freq: %.1f Hz, Vol: %.2f", frequency, volume]];
+                }
             }
         }
         
@@ -227,7 +313,7 @@
             status = @"Lid slightly open";
         } else if (angle < 90.0) {
             status = @"Lid partially open";
-        } else if (angle < 135.0) {
+        } else if (angle < 120.0) {
             status = @"Lid mostly open";
         } else {
             status = @"Lid fully open";

LidAngleSensor/CreakAudioEngine.h

@@ -2,7 +2,7 @@
 //  CreakAudioEngine.h
 //  LidAngleSensor
 //
-//  Created by Sam on 2025-01-16.
+//  Created by Sam on 2025-09-06.
 //
 
 #import <Foundation/Foundation.h>

LidAngleSensor/CreakAudioEngine.m

@@ -2,7 +2,7 @@
 //  CreakAudioEngine.m
 //  LidAngleSensor
 //
-//  Created by Sam on 2025-01-16.
+//  Created by Sam on 2025-09-06.
 //
 
 #import "CreakAudioEngine.h"

LidAngleSensor/LidAngleSensor.m

@@ -48,11 +48,13 @@
         return NULL;
     }
     
-    // Use Generic Desktop + Mouse criteria to find candidate devices
-    // This broader search allows us to find the lid sensor among other HID devices
+    // Match specifically for the lid angle sensor to avoid permission prompts
+    // Target: Sensor page (0x0020), Orientation usage (0x008A)
     NSDictionary *matchingDict = @{
-        @"UsagePage": @(0x0001),    // Generic Desktop
-        @"Usage": @(0x0003),        // Mouse
+        @"VendorID": @(0x05AC),     // Apple
+        @"ProductID": @(0x8104),    // Specific product
+        @"UsagePage": @(0x0020),    // Sensor page
+        @"Usage": @(0x008A),        // Orientation usage
     };
     
     IOHIDManagerSetDeviceMatching(manager, (__bridge CFDictionaryRef)matchingDict);
@@ -60,33 +62,38 @@
     IOHIDDeviceRef device = NULL;
     
     if (devices && CFSetGetCount(devices) > 0) {
-        NSLog(@"[LidAngleSensor] Found %ld devices, looking for sensor...", CFSetGetCount(devices));
+        NSLog(@"[LidAngleSensor] Found %ld matching lid angle sensor device(s)", CFSetGetCount(devices));
         
         const void **deviceArray = malloc(sizeof(void*) * CFSetGetCount(devices));
         CFSetGetValues(devices, deviceArray);
         
-        // Search for the specific lid angle sensor device
-        // Discovered through reverse engineering: Apple device with Sensor page
+        // Test each matching device to find the one that actually works
         for (CFIndex i = 0; i < CFSetGetCount(devices); i++) {
-            IOHIDDeviceRef currentDevice = (IOHIDDeviceRef)deviceArray[i];
+            IOHIDDeviceRef testDevice = (IOHIDDeviceRef)deviceArray[i];
             
-            CFNumberRef vendorID = IOHIDDeviceGetProperty(currentDevice, CFSTR("VendorID"));
-            CFNumberRef productID = IOHIDDeviceGetProperty(currentDevice, CFSTR("ProductID"));
-            CFNumberRef usagePage = IOHIDDeviceGetProperty(currentDevice, CFSTR("PrimaryUsagePage"));
-            CFNumberRef usage = IOHIDDeviceGetProperty(currentDevice, CFSTR("PrimaryUsage"));
-            
-            int vid = 0, pid = 0, up = 0, u = 0;
-            if (vendorID) CFNumberGetValue(vendorID, kCFNumberIntType, &vid);
-            if (productID) CFNumberGetValue(productID, kCFNumberIntType, &pid);
-            if (usagePage) CFNumberGetValue(usagePage, kCFNumberIntType, &up);
-            if (usage) CFNumberGetValue(usage, kCFNumberIntType, &u);
-            
-            // Target the specific lid angle sensor device
-            // VID=0x05AC (Apple), PID=0x8104, UsagePage=0x0020 (Sensor), Usage=0x008A (Orientation)
-            if (vid == 0x05AC && pid == 0x8104 && up == 0x0020 && u == 0x008A) {
-                device = (IOHIDDeviceRef)CFRetain(currentDevice);
-                NSLog(@"[LidAngleSensor] Found lid angle sensor device: VID=0x%04X, PID=0x%04X", vid, pid);
-                break;
+            // Try to open and read from this device
+            if (IOHIDDeviceOpen(testDevice, kIOHIDOptionsTypeNone) == kIOReturnSuccess) {
+                uint8_t testReport[8] = {0};
+                CFIndex reportLength = sizeof(testReport);
+                
+                IOReturn result = IOHIDDeviceGetReport(testDevice, 
+                                                      kIOHIDReportTypeFeature,
+                                                      1,
+                                                      testReport, 
+                                                      &reportLength);
+                
+                if (result == kIOReturnSuccess && reportLength >= 3) {
+                    // This device works! Use it.
+                    device = (IOHIDDeviceRef)CFRetain(testDevice);
+                    NSLog(@"[LidAngleSensor] Successfully found working lid angle sensor device (index %ld)", i);
+                    IOHIDDeviceClose(testDevice, kIOHIDOptionsTypeNone); // Close for now, will reopen in init
+                    break;
+                } else {
+                    NSLog(@"[LidAngleSensor] Device %ld failed to read (result: %d, length: %ld)", i, result, reportLength);
+                    IOHIDDeviceClose(testDevice, kIOHIDOptionsTypeNone);
+                }
+            } else {
+                NSLog(@"[LidAngleSensor] Failed to open device %ld", i);
             }
         }
         
@@ -119,9 +126,9 @@
     
     if (result == kIOReturnSuccess && reportLength >= 3) {
         // Data format: [report_id, angle_low, angle_high]
-        // Example: [01 72 00] = 0x7201 centidegrees = 291.85 degrees
-        uint16_t rawValue = *(uint16_t*)(report);
-        double angle = rawValue * 0.01;  // Convert centidegrees to degrees
+        // Parse the 16-bit value from bytes 1-2 (skipping report ID)
+        uint16_t rawValue = (report[2] << 8) | report[1];  // High byte, low byte
+        double angle = (double)rawValue;  // Raw value is already in degrees
         
         return angle;
     }

LidAngleSensor/NSLabel.h

@@ -2,7 +2,7 @@
 //  NSLabel.h
 //  LidAngleSensor
 //
-//  Created by Sam on 2025-01-16.
+//  Created by Sam on 2025-09-06.
 //
 
 #import <Cocoa/Cocoa.h>

LidAngleSensor/NSLabel.m

@@ -2,7 +2,7 @@
 //  NSLabel.m
 //  LidAngleSensor
 //
-//  Created by Sam on 2025-01-16.
+//  Created by Sam on 2025-09-06.
 //
 
 #import "NSLabel.h"

LidAngleSensor/ThereminAudioEngine.h

@@ -0,0 +1,62 @@
+//
+//  ThereminAudioEngine.h
+//  LidAngleSensor
+//
+//  Created by Sam on 2025-09-06.
+//
+
+#import <Foundation/Foundation.h>
+#import <AVFoundation/AVFoundation.h>
+
+/**
+ * ThereminAudioEngine provides real-time theremin-like audio that responds to MacBook lid angle changes.
+ * 
+ * Features:
+ * - Real-time sine wave synthesis based on lid angle
+ * - Smooth frequency transitions to avoid audio artifacts
+ * - Volume control based on angular velocity
+ * - Configurable frequency range mapping
+ * - Low-latency audio generation
+ * 
+ * Audio Behavior:
+ * - Lid angle maps to frequency (closed = low pitch, open = high pitch)
+ * - Movement velocity controls volume (slow movement = loud, fast = quiet)
+ * - Smooth parameter interpolation for musical quality
+ */
+@interface ThereminAudioEngine : NSObject
+
+@property (nonatomic, assign, readonly) BOOL isEngineRunning;
+@property (nonatomic, assign, readonly) double currentVelocity;
+@property (nonatomic, assign, readonly) double currentFrequency;
+@property (nonatomic, assign, readonly) double currentVolume;
+
+/**
+ * Initialize the theremin audio engine.
+ * @return Initialized engine instance, or nil if initialization failed
+ */
+- (instancetype)init;
+
+/**
+ * Start the audio engine and begin tone generation.
+ */
+- (void)startEngine;
+
+/**
+ * Stop the audio engine and halt tone generation.
+ */
+- (void)stopEngine;
+
+/**
+ * Update the theremin audio based on new lid angle measurement.
+ * This method calculates frequency mapping and volume based on movement.
+ * @param lidAngle Current lid angle in degrees
+ */
+- (void)updateWithLidAngle:(double)lidAngle;
+
+/**
+ * Manually set the angular velocity (for testing purposes).
+ * @param velocity Angular velocity in degrees per second
+ */
+- (void)setAngularVelocity:(double)velocity;
+
+@end

LidAngleSensor/ThereminAudioEngine.m

@@ -0,0 +1,318 @@
+//
+//  ThereminAudioEngine.m
+//  LidAngleSensor
+//
+//  Created by Sam on 2025-09-06.
+//
+
+#import "ThereminAudioEngine.h"
+#import <AudioToolbox/AudioToolbox.h>
+
+// Theremin parameter mapping constants
+static const double kMinFrequency = 110.0;       // Hz - A2 note (closed lid)
+static const double kMaxFrequency = 440.0;       // Hz - A4 note (open lid) - much lower range
+static const double kMinAngle = 0.0;             // degrees - closed lid
+static const double kMaxAngle = 135.0;           // degrees - fully open lid
+
+// Volume control constants - continuous tone with velocity modulation
+static const double kBaseVolume = 0.6;           // Base volume when at rest
+static const double kVelocityVolumeBoost = 0.4;  // Additional volume boost from movement
+static const double kVelocityFull = 8.0;         // deg/s - max volume boost at/under this velocity
+static const double kVelocityQuiet = 80.0;       // deg/s - no volume boost over this velocity
+
+// Vibrato constants
+static const double kVibratoFrequency = 5.0;     // Hz - vibrato rate
+static const double kVibratoDepth = 0.03;        // Vibrato depth as fraction of frequency (3%)
+
+// Smoothing constants
+static const double kAngleSmoothingFactor = 0.1;      // Moderate smoothing for frequency
+static const double kVelocitySmoothingFactor = 0.3;   // Moderate smoothing for velocity
+static const double kFrequencyRampTimeMs = 30.0;      // Frequency ramping time constant
+static const double kVolumeRampTimeMs = 50.0;         // Volume ramping time constant
+static const double kMovementThreshold = 0.3;         // Minimum angle change to register movement
+static const double kMovementTimeoutMs = 100.0;       // Time before velocity decay
+static const double kVelocityDecayFactor = 0.7;       // Decay rate when no movement
+static const double kAdditionalDecayFactor = 0.85;    // Additional decay after timeout
+
+// Audio constants
+static const double kSampleRate = 44100.0;
+static const UInt32 kBufferSize = 512;
+
+@interface ThereminAudioEngine ()
+
+// Audio engine components
+@property (nonatomic, strong) AVAudioEngine *audioEngine;
+@property (nonatomic, strong) AVAudioSourceNode *sourceNode;
+@property (nonatomic, strong) AVAudioMixerNode *mixerNode;
+
+// State tracking
+@property (nonatomic, assign) double lastLidAngle;
+@property (nonatomic, assign) double smoothedLidAngle;
+@property (nonatomic, assign) double lastUpdateTime;
+@property (nonatomic, assign) double smoothedVelocity;
+@property (nonatomic, assign) double targetFrequency;
+@property (nonatomic, assign) double targetVolume;
+@property (nonatomic, assign) double currentFrequency;
+@property (nonatomic, assign) double currentVolume;
+@property (nonatomic, assign) BOOL isFirstUpdate;
+@property (nonatomic, assign) NSTimeInterval lastMovementTime;
+
+// Sine wave generation
+@property (nonatomic, assign) double phase;
+@property (nonatomic, assign) double phaseIncrement;
+
+// Vibrato generation
+@property (nonatomic, assign) double vibratoPhase;
+
+@end
+
+@implementation ThereminAudioEngine
+
+- (instancetype)init {
+    self = [super init];
+    if (self) {
+        _isFirstUpdate = YES;
+        _lastUpdateTime = CACurrentMediaTime();
+        _lastMovementTime = CACurrentMediaTime();
+        _lastLidAngle = 0.0;
+        _smoothedLidAngle = 0.0;
+        _smoothedVelocity = 0.0;
+        _targetFrequency = kMinFrequency;
+        _targetVolume = kBaseVolume;
+        _currentFrequency = kMinFrequency;
+        _currentVolume = kBaseVolume;
+        _phase = 0.0;
+        _vibratoPhase = 0.0;
+        _phaseIncrement = 2.0 * M_PI * kMinFrequency / kSampleRate;
+        
+        if (![self setupAudioEngine]) {
+            NSLog(@"[ThereminAudioEngine] Failed to setup audio engine");
+            return nil;
+        }
+    }
+    return self;
+}
+
+- (void)dealloc {
+    [self stopEngine];
+}
+
+#pragma mark - Audio Engine Setup
+
+- (BOOL)setupAudioEngine {
+    self.audioEngine = [[AVAudioEngine alloc] init];
+    self.mixerNode = self.audioEngine.mainMixerNode;
+    
+    // Create audio format for our sine wave
+    AVAudioFormat *format = [[AVAudioFormat alloc] initWithCommonFormat:AVAudioPCMFormatFloat32
+                                                             sampleRate:kSampleRate
+                                                               channels:1
+                                                            interleaved:NO];
+    
+    // Create source node for sine wave generation
+    __weak typeof(self) weakSelf = self;
+    self.sourceNode = [[AVAudioSourceNode alloc] initWithFormat:format renderBlock:^OSStatus(BOOL * _Nonnull isSilence, const AudioTimeStamp * _Nonnull timestamp, AVAudioFrameCount frameCount, AudioBufferList * _Nonnull outputData) {
+        return [weakSelf renderSineWave:isSilence timestamp:timestamp frameCount:frameCount outputData:outputData];
+    }];
+    
+    // Attach and connect the source node
+    [self.audioEngine attachNode:self.sourceNode];
+    [self.audioEngine connect:self.sourceNode to:self.mixerNode format:format];
+    
+    return YES;
+}
+
+#pragma mark - Engine Control
+
+- (void)startEngine {
+    if (self.isEngineRunning) {
+        return;
+    }
+    
+    NSError *error;
+    if (![self.audioEngine startAndReturnError:&error]) {
+        NSLog(@"[ThereminAudioEngine] Failed to start audio engine: %@", error.localizedDescription);
+        return;
+    }
+    
+    NSLog(@"[ThereminAudioEngine] Started theremin engine");
+}
+
+- (void)stopEngine {
+    if (!self.isEngineRunning) {
+        return;
+    }
+    
+    [self.audioEngine stop];
+    NSLog(@"[ThereminAudioEngine] Stopped theremin engine");
+}
+
+- (BOOL)isEngineRunning {
+    return self.audioEngine.isRunning;
+}
+
+#pragma mark - Sine Wave Generation
+
+- (OSStatus)renderSineWave:(BOOL *)isSilence
+                 timestamp:(const AudioTimeStamp *)timestamp
+                frameCount:(AVAudioFrameCount)frameCount
+                outputData:(AudioBufferList *)outputData {
+    
+    float *output = (float *)outputData->mBuffers[0].mData;
+    
+    // Always generate sound (continuous tone)
+    *isSilence = NO;
+    
+    // Calculate vibrato phase increment
+    double vibratoPhaseIncrement = 2.0 * M_PI * kVibratoFrequency / kSampleRate;
+    
+    // Generate sine wave samples with vibrato
+    for (AVAudioFrameCount i = 0; i < frameCount; i++) {
+        // Calculate vibrato modulation
+        double vibratoModulation = sin(self.vibratoPhase) * kVibratoDepth;
+        double modulatedFrequency = self.currentFrequency * (1.0 + vibratoModulation);
+        
+        // Update phase increment for modulated frequency
+        self.phaseIncrement = 2.0 * M_PI * modulatedFrequency / kSampleRate;
+        
+        // Generate sample with vibrato and current volume
+        output[i] = (float)(sin(self.phase) * self.currentVolume * 0.25); // 0.25 to prevent clipping
+        
+        // Update phases
+        self.phase += self.phaseIncrement;
+        self.vibratoPhase += vibratoPhaseIncrement;
+        
+        // Wrap phases to prevent accumulation of floating point errors
+        if (self.phase >= 2.0 * M_PI) {
+            self.phase -= 2.0 * M_PI;
+        }
+        if (self.vibratoPhase >= 2.0 * M_PI) {
+            self.vibratoPhase -= 2.0 * M_PI;
+        }
+    }
+    
+    return noErr;
+}
+
+#pragma mark - Lid Angle Processing
+
+- (void)updateWithLidAngle:(double)lidAngle {
+    double currentTime = CACurrentMediaTime();
+    
+    if (self.isFirstUpdate) {
+        self.lastLidAngle = lidAngle;
+        self.smoothedLidAngle = lidAngle;
+        self.lastUpdateTime = currentTime;
+        self.lastMovementTime = currentTime;
+        self.isFirstUpdate = NO;
+        
+        // Set initial frequency based on angle
+        [self updateTargetParametersWithAngle:lidAngle velocity:0.0];
+        return;
+    }
+    
+    // Calculate time delta
+    double deltaTime = currentTime - self.lastUpdateTime;
+    if (deltaTime <= 0 || deltaTime > 1.0) {
+        // Skip if time delta is invalid or too large
+        self.lastUpdateTime = currentTime;
+        return;
+    }
+    
+    // Stage 1: Smooth the raw angle input
+    self.smoothedLidAngle = (kAngleSmoothingFactor * lidAngle) + 
+                           ((1.0 - kAngleSmoothingFactor) * self.smoothedLidAngle);
+    
+    // Stage 2: Calculate velocity from smoothed angle data
+    double deltaAngle = self.smoothedLidAngle - self.lastLidAngle;
+    double instantVelocity;
+    
+    // Apply movement threshold
+    if (fabs(deltaAngle) < kMovementThreshold) {
+        instantVelocity = 0.0;
+    } else {
+        instantVelocity = fabs(deltaAngle / deltaTime);
+        self.lastLidAngle = self.smoothedLidAngle;
+    }
+    
+    // Stage 3: Apply velocity smoothing and decay
+    if (instantVelocity > 0.0) {
+        self.smoothedVelocity = (kVelocitySmoothingFactor * instantVelocity) + 
+                               ((1.0 - kVelocitySmoothingFactor) * self.smoothedVelocity);
+        self.lastMovementTime = currentTime;
+    } else {
+        self.smoothedVelocity *= kVelocityDecayFactor;
+    }
+    
+    // Additional decay if no movement for extended period
+    double timeSinceMovement = currentTime - self.lastMovementTime;
+    if (timeSinceMovement > (kMovementTimeoutMs / 1000.0)) {
+        self.smoothedVelocity *= kAdditionalDecayFactor;
+    }
+    
+    // Update state for next iteration
+    self.lastUpdateTime = currentTime;
+    
+    // Update target parameters
+    [self updateTargetParametersWithAngle:self.smoothedLidAngle velocity:self.smoothedVelocity];
+    
+    // Apply smooth parameter transitions
+    [self rampToTargetParameters];
+}
+
+- (void)setAngularVelocity:(double)velocity {
+    self.smoothedVelocity = velocity;
+    [self updateTargetParametersWithAngle:self.smoothedLidAngle velocity:velocity];
+    [self rampToTargetParameters];
+}
+
+- (void)updateTargetParametersWithAngle:(double)angle velocity:(double)velocity {
+    // Map angle to frequency using exponential curve for musical feel
+    double normalizedAngle = fmax(0.0, fmin(1.0, (angle - kMinAngle) / (kMaxAngle - kMinAngle)));
+    
+    // Use exponential mapping for more musical frequency distribution
+    double frequencyRatio = pow(normalizedAngle, 0.7); // Slight compression for better control
+    self.targetFrequency = kMinFrequency + frequencyRatio * (kMaxFrequency - kMinFrequency);
+    
+    // Calculate continuous volume with velocity-based boost
+    double velocityBoost = 0.0;
+    if (velocity > 0.0) {
+        // Use smoothstep curve for natural volume boost response
+        double e0 = 0.0;
+        double e1 = kVelocityQuiet;
+        double t = fmin(1.0, fmax(0.0, (velocity - e0) / (e1 - e0)));
+        double s = t * t * (3.0 - 2.0 * t); // smoothstep function
+        velocityBoost = (1.0 - s) * kVelocityVolumeBoost; // invert: slow = more boost, fast = less boost
+    }
+    
+    // Combine base volume with velocity boost
+    self.targetVolume = kBaseVolume + velocityBoost;
+    self.targetVolume = fmax(0.0, fmin(1.0, self.targetVolume));
+}
+
+// Helper function for parameter ramping
+- (double)rampValue:(double)current toward:(double)target withDeltaTime:(double)dt timeConstantMs:(double)tauMs {
+    double alpha = fmin(1.0, dt / (tauMs / 1000.0));
+    return current + (target - current) * alpha;
+}
+
+- (void)rampToTargetParameters {
+    // Calculate delta time for ramping
+    static double lastRampTime = 0;
+    double currentTime = CACurrentMediaTime();
+    if (lastRampTime == 0) lastRampTime = currentTime;
+    double deltaTime = currentTime - lastRampTime;
+    lastRampTime = currentTime;
+    
+    // Ramp current values toward targets for smooth transitions
+    self.currentFrequency = [self rampValue:self.currentFrequency toward:self.targetFrequency withDeltaTime:deltaTime timeConstantMs:kFrequencyRampTimeMs];
+    self.currentVolume = [self rampValue:self.currentVolume toward:self.targetVolume withDeltaTime:deltaTime timeConstantMs:kVolumeRampTimeMs];
+}
+
+#pragma mark - Property Accessors
+
+- (double)currentVelocity {
+    return self.smoothedVelocity;
+}
+
+@end

README.md

@@ -33,3 +33,7 @@ I guess.
 **How come the audio feels kind of...weird?**
 
 I'm bad at audio.
+
+**Where did the sound effect come from?**
+
+LEGO Batman 3: Beyond Gotham. But you knew that already.