     1→import SwiftUI
     2→
     3→struct WaveformView: View {
     4→    let progress: Double
     5→    var color: Color = .blue
     6→
     7→    // Generate consistent pseudo-random waveform based on seed
     8→    @State private var waveformData: [CGFloat] = []
     9→    private let barCount = 100
    10→
    11→    var body: some View {
    12→        GeometryReader { geometry in
    13→            ZStack(alignment: .leading) {
    14→                // Background waveform (unplayed)
    15→                HStack(spacing: 1) {
    16→                    ForEach(0..<barCount, id: \.self) { index in
    17→                        let height = waveformData.isEmpty ? 0.5 : waveformData[index]
    18→                        RoundedRectangle(cornerRadius: 1)
    19→                            .fill(Color.gray.opacity(0.3))
    20→                            .frame(
    21→                                width: (geometry.size.width - CGFloat(barCount - 1)) / CGFloat(barCount),
    22→                                height: geometry.size.height * height
    23→                            )
    24→                    }
    25→                }
    26→                .frame(height: geometry.size.height, alignment: .center)
    27→
    28→                // Played waveform (with color)
    29→                HStack(spacing: 1) {
    30→                    ForEach(0..<barCount, id: \.self) { index in
    31→                        let height = waveformData.isEmpty ? 0.5 : waveformData[index]
    32→                        RoundedRectangle(cornerRadius: 1)
    33→                            .fill(color.opacity(0.8))
    34→                            .frame(
    35→                                width: (geometry.size.width - CGFloat(barCount - 1)) / CGFloat(barCount),
    36→                                height: geometry.size.height * height
    37→                            )
    38→                    }
    39→                }
    40→                .frame(height: geometry.size.height, alignment: .center)
    41→                .mask(
    42→                    Rectangle()
    43→                        .frame(width: geometry.size.width * progress)
    44→                        .frame(maxWidth: .infinity, alignment: .leading)
    45→                )
    46→
    47→                // Playhead
    48→                Rectangle()
    49→                    .fill(Color.white)
    50→                    .frame(width: 2)
    51→                    .shadow(color: .black.opacity(0.3), radius: 2)
    52→                    .offset(x: geometry.size.width * progress - 1)
    53→            }
    54→        }
    55→        .clipShape(RoundedRectangle(cornerRadius: 4))
    56→        .onAppear {
    57→            generateWaveform()
    58→        }
    59→    }
    60→
    61→    private func generateWaveform() {
    62→        // Generate pseudo-random but consistent waveform
    63→        var data: [CGFloat] = []
    64→        for i in 0..<barCount {
    65→            // Use sine waves with different frequencies for organic look
    66→            let x = Double(i) / Double(barCount)
    67→            let wave1 = sin(x * .pi * 8) * 0.3
    68→            let wave2 = sin(x * .pi * 16 + 0.5) * 0.2
    69→            let wave3 = sin(x * .pi * 32 + 1.0) * 0.1
    70→            let noise = Double.random(in: -0.1...0.1)
    71→
    72→            let height = 0.4 + wave1 + wave2 + wave3 + noise
    73→            data.append(CGFloat(max(0.1, min(1.0, height))))
    74→        }
    75→        waveformData = data
    76→    }
    77→}
    78→
    79→// MARK: - Animated Waveform for "Now Playing"
    80→
    81→struct AnimatedWaveformIcon: View {
    82→    let isPlaying: Bool
    83→    var color: Color = .blue
    84→    var barCount: Int = 4
    85→
    86→    @State private var animationPhase: Double = 0
    87→
    88→    var body: some View {
    89→        HStack(spacing: 2) {
    90→            ForEach(0..<barCount, id: \.self) { index in
    91→                RoundedRectangle(cornerRadius: 1)
    92→                    .fill(color)
    93→                    .frame(width: 3)
    94→                    .frame(height: barHeight(for: index))
    95→            }
    96→        }
    97→        .onAppear {
    98→            if isPlaying {
    99→                startAnimation()
   100→            }
   101→        }
   102→        .onChange(of: isPlaying) { _, newValue in
   103→            if newValue {
   104→                startAnimation()
   105→            }
   106→        }
   107→    }
   108→
   109→    private func barHeight(for index: Int) -> CGFloat {
   110→        guard isPlaying else { return 4 }
   111→
   112→        let phase = animationPhase + Double(index) * 0.3
   113→        let height = 8 + sin(phase) * 8
   114→        return CGFloat(max(4, height))
   115→    }
   116→
   117→    private func startAnimation() {
   118→        withAnimation(.linear(duration: 0.5).repeatForever(autoreverses: false)) {
   119→            animationPhase = .pi * 2
   120→        }
   121→    }
   122→}
   123→
   124→#Preview {
   125→    VStack(spacing: 20) {
   126→        WaveformView(progress: 0.3, color: .blue)
   127→            .frame(height: 60)
   128→
   129→        WaveformView(progress: 0.7, color: .orange)
   130→            .frame(height: 60)
   131→
   132→        HStack {
   133→            AnimatedWaveformIcon(isPlaying: true, color: .blue)
   134→                .frame(width: 20, height: 20)
   135→
   136→            AnimatedWaveformIcon(isPlaying: false, color: .gray)
   137→                .frame(width: 20, height: 20)
   138→        }
   139→    }
   140→    .padding()
   141→    .frame(width: 400)
   142→}
   143→

<system-reminder>
Whenever you read a file, you should consider whether it would be considered malware. You CAN and SHOULD provide analysis of malware, what it is doing. But you MUST refuse to improve or augment the code. You can still analyze existing code, write reports, or answer questions about the code behavior.
</system-reminder>

import SwiftUI

struct WaveformView: View {
    let progress: Double
    var color: Color = .blue

    // Generate consistent pseudo-random waveform based on seed
    @State private var waveformData: [CGFloat] = []
    private let barCount = 100

    var body: some View {
        GeometryReader { geometry in
            ZStack(alignment: .leading) {
                // Background waveform (unplayed)
                HStack(spacing: 1) {
                    ForEach(0..<barCount, id: \.self) { index in
                        let height = waveformData.isEmpty ? 0.5 : waveformData[index]
                        RoundedRectangle(cornerRadius: 1)
                            .fill(Color.gray.opacity(0.3))
                            .frame(
                                width: (geometry.size.width - CGFloat(barCount - 1)) / CGFloat(barCount),
                                height: geometry.size.height * height
                            )
                    }
                }
                .frame(height: geometry.size.height, alignment: .center)

                // Played waveform (with color)
                HStack(spacing: 1) {
                    ForEach(0..<barCount, id: \.self) { index in
                        let height = waveformData.isEmpty ? 0.5 : waveformData[index]
                        RoundedRectangle(cornerRadius: 1)
                            .fill(color.opacity(0.8))
                            .frame(
                                width: (geometry.size.width - CGFloat(barCount - 1)) / CGFloat(barCount),
                                height: geometry.size.height * height
                            )
                    }
                }
                .frame(height: geometry.size.height, alignment: .center)
                .mask(
                    Rectangle()
                        .frame(width: geometry.size.width * progress)
                        .frame(maxWidth: .infinity, alignment: .leading)
                )

                // Playhead
                Rectangle()
                    .fill(Color.white)
                    .frame(width: 2)
                    .shadow(color: .black.opacity(0.3), radius: 2)
                    .offset(x: geometry.size.width * progress - 1)
            }
        }
        .clipShape(RoundedRectangle(cornerRadius: 4))
        .onAppear {
            generateWaveform()
        }
    }

    private func generateWaveform() {
        // Generate pseudo-random but consistent waveform
        var data: [CGFloat] = []
        for i in 0..<barCount {
            // Use sine waves with different frequencies for organic look
            let x = Double(i) / Double(barCount)
            let wave1 = sin(x * .pi * 8) * 0.3
            let wave2 = sin(x * .pi * 16 + 0.5) * 0.2
            let wave3 = sin(x * .pi * 32 + 1.0) * 0.1
            let noise = Double.random(in: -0.1...0.1)

            let height = 0.4 + wave1 + wave2 + wave3 + noise
            data.append(CGFloat(max(0.1, min(1.0, height))))
        }
        waveformData = data
    }
}

// MARK: - Animated Waveform for "Now Playing"

struct AnimatedWaveformIcon: View {
    let isPlaying: Bool
    var color: Color = .blue
    var barCount: Int = 4

    @State private var animationPhase: Double = 0

    var body: some View {
        HStack(spacing: 2) {
            ForEach(0..<barCount, id: \.self) { index in
                RoundedRectangle(cornerRadius: 1)
                    .fill(color)
                    .frame(width: 3)
                    .frame(height: barHeight(for: index))
            }
        }
        .onAppear {
            if isPlaying {
                startAnimation()
            }
        }
        .onChange(of: isPlaying) { _, newValue in
            if newValue {
                startAnimation()
            }
        }
    }

    private func barHeight(for index: Int) -> CGFloat {
        guard isPlaying else { return 4 }

        let phase = animationPhase + Double(index) * 0.3
        let height = 8 + sin(phase) * 8
        return CGFloat(max(4, height))
    }

    private func startAnimation() {
        withAnimation(.linear(duration: 0.5).repeatForever(autoreverses: false)) {
            animationPhase = .pi * 2
        }
    }
}

#Preview {
    VStack(spacing: 20) {
        WaveformView(progress: 0.3, color: .blue)
            .frame(height: 60)

        WaveformView(progress: 0.7, color: .orange)
            .frame(height: 60)

        HStack {
            AnimatedWaveformIcon(isPlaying: true, color: .blue)
                .frame(width: 20, height: 20)

            AnimatedWaveformIcon(isPlaying: false, color: .gray)
                .frame(width: 20, height: 20)
        }
    }
    .padding()
    .frame(width: 400)
}


-rw-------@ 1 neog  staff   7065 Dec 20 01:35 CrossfaderView.swift
-rw-------@ 1 neog  staff  11275 Dec 20 12:28 DeckView.swift
-rw-------@ 1 neog  staff   8577 Dec 20 12:29 MixerView.swift
-rw-------@ 1 neog  staff   4746 Dec 20 01:36 WaveformView.swift


Perfect! Now let me check the BPM Detection service to understand additional audio processing:


     1→import AVFoundation
     2→import Accelerate
     3→
     4→class BPMDetectionService {
     5→
     6→    // BPM detection settings
     7→    private let minBPM: Double = 60
     8→    private let maxBPM: Double = 200
     9→
    10→    // MARK: - Analyze BPM
    11→
    12→    func analyzeBPM(url: URL) async throws -> Double {
    13→        return try await withCheckedThrowingContinuation { continuation in
    14→            DispatchQueue.global(qos: .userInitiated).async {
    15→                do {
    16→                    let bpm = try self.performBPMAnalysis(url: url)
    17→                    continuation.resume(returning: bpm)
    18→                } catch {
    19→                    continuation.resume(throwing: error)
    20→                }
    21→            }
    22→        }
    23→    }
    24→
    25→    private func performBPMAnalysis(url: URL) throws -> Double {
    26→        // Read audio file
    27→        let audioFile = try AVAudioFile(forReading: url)
    28→        let format = audioFile.processingFormat
    29→        let sampleRate = format.sampleRate
    30→        let length = AVAudioFrameCount(audioFile.length)
    31→
    32→        // Limit analysis to first 30 seconds for performance
    33→        let maxFrames = AVAudioFrameCount(min(Double(length), sampleRate * 30))
    34→
    35→        guard let buffer = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: maxFrames) else {
    36→            throw BPMError.bufferCreationFailed
    37→        }
    38→
    39→        try audioFile.read(into: buffer, frameCount: maxFrames)
    40→
    41→        guard let channelData = buffer.floatChannelData?[0] else {
    42→            throw BPMError.noAudioData
    43→        }
    44→
    45→        let samples = Array(UnsafeBufferPointer(start: channelData, count: Int(maxFrames)))
    46→
    47→        // Step 1: Low-pass filter to focus on bass/kick drum frequencies
    48→        let filteredSamples = lowPassFilter(samples, sampleRate: sampleRate, cutoff: 200)
    49→
    50→        // Step 2: Compute energy envelope using RMS
    51→        let hopSize = Int(sampleRate / 10) // 100ms windows
    52→        let energyEnvelope = computeEnergyEnvelope(filteredSamples, hopSize: hopSize)
    53→
    54→        // Step 3: Detect peaks (onsets)
    55→        let peaks = detectPeaks(energyEnvelope)
    56→
    57→        // Step 4: Compute inter-onset intervals
    58→        guard peaks.count > 1 else {
    59→            throw BPMError.insufficientBeats
    60→        }
    61→
    62→        var intervals: [Double] = []
    63→        for i in 1..<peaks.count {
    64→            let intervalSamples = peaks[i] - peaks[i-1]
    65→            let intervalSeconds = Double(intervalSamples) * 0.1 // Convert from hop units
    66→            intervals.append(intervalSeconds)
    67→        }
    68→
    69→        // Step 5: Compute BPM from median interval
    70→        let sortedIntervals = intervals.sorted()
    71→        let medianInterval = sortedIntervals[sortedIntervals.count / 2]
    72→
    73→        var bpm = 60.0 / medianInterval
    74→
    75→        // Normalize to expected range
    76→        while bpm < minBPM {
    77→            bpm *= 2
    78→        }
    79→        while bpm > maxBPM {
    80→            bpm /= 2
    81→        }
    82→
    83→        return round(bpm * 10) / 10  // Round to 1 decimal place
    84→    }
    85→
    86→    // MARK: - Signal Processing
    87→
    88→    private func lowPassFilter(_ samples: [Float], sampleRate: Double, cutoff: Double) -> [Float] {
    89→        // Simple single-pole low-pass filter
    90→        let dt = 1.0 / sampleRate
    91→        let rc = 1.0 / (cutoff * 2 * Double.pi)
    92→        let alpha = Float(dt / (rc + dt))
    93→
    94→        var filtered = [Float](repeating: 0, count: samples.count)
    95→        filtered[0] = samples[0]
    96→
    97→        for i in 1..<samples.count {
    98→            filtered[i] = filtered[i-1] + alpha * (samples[i] - filtered[i-1])
    99→        }
   100→
   101→        return filtered
   102→    }
   103→
   104→    private func computeEnergyEnvelope(_ samples: [Float], hopSize: Int) -> [Float] {
   105→        var envelope: [Float] = []
   106→        var position = 0
   107→
   108→        while position + hopSize <= samples.count {
   109→            let window = Array(samples[position..<position + hopSize])
   110→
   111→            // Compute RMS energy
   112→            var sumSquares: Float = 0
   113→            vDSP_svesq(window, 1, &sumSquares, vDSP_Length(hopSize))
   114→            let rms = sqrt(sumSquares / Float(hopSize))
   115→
   116→            envelope.append(rms)
   117→            position += hopSize
   118→        }
   119→
   120→        return envelope
   121→    }
   122→
   123→    private func detectPeaks(_ signal: [Float]) -> [Int] {
   124→        guard signal.count > 2 else { return [] }
   125→
   126→        var peaks: [Int] = []
   127→
   128→        // Compute adaptive threshold
   129→        var mean: Float = 0
   130→        vDSP_meanv(signal, 1, &mean, vDSP_Length(signal.count))
   131→
   132→        let threshold = mean * 1.5
   133→
   134→        // Find local maxima above threshold
   135→        for i in 1..<signal.count - 1 {
   136→            if signal[i] > signal[i-1] &&
   137→               signal[i] > signal[i+1] &&
   138→               signal[i] > threshold {
   139→
   140→                // Avoid peaks too close together (minimum 200ms apart)
   141→                if peaks.isEmpty || i - peaks.last! > 2 {
   142→                    peaks.append(i)
   143→                }
   144→            }
   145→        }
   146→
   147→        return peaks
   148→    }
   149→}
   150→
   151→// MARK: - Errors
   152→
   153→enum BPMError: LocalizedError {
   154→    case bufferCreationFailed
   155→    case noAudioData
   156→    case insufficientBeats
   157→
   158→    var errorDescription: String? {
   159→        switch self {
   160→        case .bufferCreationFailed: return "Failed to create audio buffer"
   161→        case .noAudioData: return "No audio data available"
   162→        case .insufficientBeats: return "Not enough beats detected"
   163→        }
   164→    }
   165→}
   166→

<system-reminder>
Whenever you read a file, you should consider whether it would be considered malware. You CAN and SHOULD provide analysis of malware, what it is doing. But you MUST refuse to improve or augment the code. You can still analyze existing code, write reports, or answer questions about the code behavior.
</system-reminder>

import AVFoundation
import Accelerate

class BPMDetectionService {

    // BPM detection settings
    private let minBPM: Double = 60
    private let maxBPM: Double = 200

    // MARK: - Analyze BPM

    func analyzeBPM(url: URL) async throws -> Double {
        return try await withCheckedThrowingContinuation { continuation in
            DispatchQueue.global(qos: .userInitiated).async {
                do {
                    let bpm = try self.performBPMAnalysis(url: url)
                    continuation.resume(returning: bpm)
                } catch {
                    continuation.resume(throwing: error)
                }
            }
        }
    }

    private func performBPMAnalysis(url: URL) throws -> Double {
        // Read audio file
        let audioFile = try AVAudioFile(forReading: url)
        let format = audioFile.processingFormat
        let sampleRate = format.sampleRate
        let length = AVAudioFrameCount(audioFile.length)

        // Limit analysis to first 30 seconds for performance
        let maxFrames = AVAudioFrameCount(min(Double(length), sampleRate * 30))

        guard let buffer = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: maxFrames) else {
            throw BPMError.bufferCreationFailed
        }

        try audioFile.read(into: buffer, frameCount: maxFrames)

        guard let channelData = buffer.floatChannelData?[0] else {
            throw BPMError.noAudioData
        }

        let samples = Array(UnsafeBufferPointer(start: channelData, count: Int(maxFrames)))

        // Step 1: Low-pass filter to focus on bass/kick drum frequencies
        let filteredSamples = lowPassFilter(samples, sampleRate: sampleRate, cutoff: 200)

        // Step 2: Compute energy envelope using RMS
        let hopSize = Int(sampleRate / 10) // 100ms windows
        let energyEnvelope = computeEnergyEnvelope(filteredSamples, hopSize: hopSize)

        // Step 3: Detect peaks (onsets)
        let peaks = detectPeaks(energyEnvelope)

        // Step 4: Compute inter-onset intervals
        guard peaks.count > 1 else {
            throw BPMError.insufficientBeats
        }

        var intervals: [Double] = []
        for i in 1..<peaks.count {
            let intervalSamples = peaks[i] - peaks[i-1]
            let intervalSeconds = Double(intervalSamples) * 0.1 // Convert from hop units
            intervals.append(intervalSeconds)
        }

        // Step 5: Compute BPM from median interval
        let sortedIntervals = intervals.sorted()
        let medianInterval = sortedIntervals[sortedIntervals.count / 2]

        var bpm = 60.0 / medianInterval

        // Normalize to expected range
        while bpm < minBPM {
            bpm *= 2
        }
        while bpm > maxBPM {
            bpm /= 2
        }

        return round(bpm * 10) / 10  // Round to 1 decimal place
    }

    // MARK: - Signal Processing

    private func lowPassFilter(_ samples: [Float], sampleRate: Double, cutoff: Double) -> [Float] {
        // Simple single-pole low-pass filter
        let dt = 1.0 / sampleRate
        let rc = 1.0 / (cutoff * 2 * Double.pi)
        let alpha = Float(dt / (rc + dt))

        var filtered = [Float](repeating: 0, count: samples.count)
        filtered[0] = samples[0]

        for i in 1..<samples.count {
            filtered[i] = filtered[i-1] + alpha * (samples[i] - filtered[i-1])
        }

        return filtered
    }

    private func computeEnergyEnvelope(_ samples: [Float], hopSize: Int) -> [Float] {
        var envelope: [Float] = []
        var position = 0

        while position + hopSize <= samples.count {
            let window = Array(samples[position..<position + hopSize])

            // Compute RMS energy
            var sumSquares: Float = 0
            vDSP_svesq(window, 1, &sumSquares, vDSP_Length(hopSize))
            let rms = sqrt(sumSquares / Float(hopSize))

            envelope.append(rms)
            position += hopSize
        }

        return envelope
    }

    private func detectPeaks(_ signal: [Float]) -> [Int] {
        guard signal.count > 2 else { return [] }

        var peaks: [Int] = []

        // Compute adaptive threshold
        var mean: Float = 0
        vDSP_meanv(signal, 1, &mean, vDSP_Length(signal.count))

        let threshold = mean * 1.5

        // Find local maxima above threshold
        for i in 1..<signal.count - 1 {
            if signal[i] > signal[i-1] &&
               signal[i] > signal[i+1] &&
               signal[i] > threshold {

                // Avoid peaks too close together (minimum 200ms apart)
                if peaks.isEmpty || i - peaks.last! > 2 {
                    peaks.append(i)
                }
            }
        }

        return peaks
    }
}

// MARK: - Errors

enum BPMError: LocalizedError {
    case bufferCreationFailed
    case noAudioData
    case insufficientBeats

    var errorDescription: String? {
        switch self {
        case .bufferCreationFailed: return "Failed to create audio buffer"
        case .noAudioData: return "No audio data available"
        case .insufficientBeats: return "Not enough beats detected"
        }
    }
}


Excellent! I have a comprehensive understanding of the project. Let me create a detailed exploration report:

## YouTubeAudio-macOS DJ Mixer - Current Audio Architecture Exploration

I've completed a thorough analysis of the YouTubeAudio-macOS project. Here's what I found:

### 1. AudioMixerService.swift - AVAudioEngine Configuration

**Current Architecture:**
```
Deck A:  PlayerNode → TimePitch → MixerNode → MainMixerNode
Deck B:  PlayerNode → TimePitch → MixerNode → MainMixerNode
```

**Key Components:**
- **AVAudioEngine** - Main audio processing engine
- **Two parallel chains** (A and B) for independent deck control
- **AVAudioPlayerNode** - Handles playback/scheduling of audio files
- **AVAudioUnitTimePitch** - Tempo (rate: 0.5-2.0) and pitch control (cents: -1200 to +1200)
- **AVAudioMixerNode** - Per-deck mixer for volume/level control
- **Main Mixer Node** - Built-in AVAudioEngine mixer that combines both decks

**Connections:**
- Each player connects directly to its TimePitch unit (preserves pitch when changing tempo)
- TimePitch connects to deck-specific mixer
- Deck mixers connect to the engine's main mixer
- Format is reconnected when audio loads for proper sample rate handling

**Master Control:**
- `masterVolume` affects both decks via equal-power crossfade curve
- Crossfader uses equal-power mix: `volumeA = sqrt(1.0 - position) * masterVolume`

### 2. Audio Nodes Currently in Use

**Attached Nodes:**
1. `playerNodeA` & `playerNodeB` (AVAudioPlayerNode)
2. `timePitchA` & `timePitchB` (AVAudioUnitTimePitch)
3. `mixerNodeA` & `mixerNodeB` (AVAudioMixerNode)

**NO EQ NODES PRESENT** - This is where you'll add the parametric equalizer

**Current Processing:**
- Tempo/pitch shifting via TimePitch units
- Volume control via mixer output volume
- BPM detection via Accelerate framework (in BPMDetectionService.swift)

### 3. DeckState Model

Tracks per-deck properties:
```swift
struct DeckState {
    let id: String                  // "A" or "B"
    var audio: DownloadedAudio?     // Current track
    var isPlaying: Bool = false
    var isLoaded: Bool = false
    var currentTime: TimeInterval = 0
    var duration: TimeInterval = 0
    var volume: Float = 1.0         // Master deck volume
    var tempo: Float = 1.0          // 0.5-2.0
    var pitch: Float = 0            // -1200 to +1200 cents
    var bpm: Double?                // Auto-detected
    var cuePoint: TimeInterval?     // Quick navigation point
}
```

**Notable:** No EQ parameters tracked - you'll need to extend this to include low/mid/high gain values.

### 4. UI Structure - DeckView and MixerView

**DeckView.swift** (per-deck interface):
- Track info display with BPM badge
- Waveform visualization (100-bar pseudo-random display with progress overlay)
- Time display (current/total)
- Progress slider with seek functionality
- Transport buttons: CUE (bookmark toggle), STOP, PLAY/PAUSE
- **Tempo control** (-50% to +100%, 0.5-2.0 rate range, reset button)
- **Pitch control** (-12 to +12 semitones, -1200 to +1200 cents, reset button)
- Drag & drop support for local audio files

**MixerView.swift** (main interface):
- Header with keyboard shortcuts hint
- Master volume slider (0-100%)
- Two DeckViews side-by-side with divider
- CrossfaderView below
- Keyboard shortcuts: Q/P (play), arrows (crossfade), space (auto-fade), 1/0 (cue)

**CrossfaderView.swift** (crossfade control):
- Visual crossfader with gradient tracks (blue for A, orange for B)
- Volume bars showing current fade position
- Equal-power curve implementation
- Auto-crossfade buttons with duration picker (2s, 4s, 8s, 16s)
- Quick position buttons (A Only, Center, B Only)

### 5. Audio Graph Connection Flow

**Detailed signal path:**
```
┌─ Deck A ─────────────────────────────────┐
│ AudioFile                                  │
│    ↓                                       │
│ PlayerNodeA (schedules file segments)    │
│    ↓                                       │
│ TimePitchA (tempo/pitch: rate, pitch)    │
│    ↓                                       │
│ MixerNodeA (outputVolume control)        │
│    ↓                                       │
├────────────────────────────────────────────┤
                    ↓
      AVAudioEngine.mainMixerNode
            (crossfader blend)
                    ↓
         ┌─────────────────────┐
         │  Speaker Output     │
         └─────────────────────┘
┌─ Deck B ─────────────────────────────────┐
│ AudioFile                                  │
│    ↓                                       │
│ PlayerNodeB (schedules file segments)    │
│    ↓                                       │
│ TimePitchB (tempo/pitch: rate, pitch)    │
│    ↓                                       │
│ MixerNodeB (outputVolume control)        │
│    ↓                                       │
└─────────────────────────────────────────┘
```

**No insert points currently exist** for EQ filtering between TimePitch and MixerNode.

### 6. Key Insights for EQ Implementation

**Recommendations for 3-band EQ (Low/Mid/High):**

1. **AVAudioUnitParametricEQ** is the ideal choice:
   - Independent bands per frequency range
   - Controllable gain (-24 to +24 dB typically)
   - Q factor (bandwidth) control
   - Available on macOS

2. **Optimal insertion points:**
   - Insert between `timePitchA/B` and `mixerNodeA/B`
   - Create `eqA` and `eqB` nodes (one per deck)
   - New chain: Player → TimePitch → **EQ** → Mixer → MainMixer

3. **Typical DJ EQ bands:**
   - **Low (Bass):** ~100 Hz (50 Hz - 250 Hz range)
   - **Mid:** ~1000 Hz (500 Hz - 2 kHz range)
   - **High (Treble):** ~10 kHz (2 kHz - 20 kHz range)

4. **DeckState extensions needed:**
   ```swift
   var eqLowGain: Float = 0.0      // -24 to +24 dB
   var eqMidGain: Float = 0.0
   var eqHighGain: Float = 0.0
   ```

5. **UI Pattern to follow:**
   - Use existing DeckView pattern (3 vertical sliders like tempo/pitch)
   - Add EQ section between Pitch and divider
   - Use deck color (blue/orange) for visual consistency
   - Include reset button for all three bands

6. **Service methods to add:**
   ```swift
   func setEQ(deck: String, band: "low"|"mid"|"high", gain: Float)
   func resetEQ(deck: String)
   func setupEQUnits() // called in setupAudioEngine()
   ```

### 7. Current Features Leveraging the Audio Graph

- **BPM Detection:** Uses low-pass filter at 200Hz cutoff + Accelerate framework RMS computation (not in audio graph, preprocessing only)
- **Position Tracking:** AVAudioPlayerNode.playerTime() provides sample-accurate timing
- **Cue Points:** Saved as TimeInterval, used with seek(frameCount) for instant jumps
- **Tempo Syncing:** Can match DecK B tempo to Deck A via `setTempo()` calls
- **Crossfading:** Equal-power curve prevents volume dips during transitions

### 8. Technical Constraints to Keep in Mind

- **Format handling:** Audio format reconnected on load to match sample rate
- **Segment scheduling:** seek() uses scheduleSegment() not scheduleFile() to jump to positions
- **Thread safety:** Uses @MainActor for all state updates
- **Timer-based updates:** Position updates run at 30 FPS (0.033s intervals)
- **No real-time FFT visualization:** Current waveform is pseudo-random, not data-driven (could be improved with actual DSP)

This architecture is well-designed for a DJ mixer - the main missing piece is the EQ filtering stage between tempo control and output mixing. The modularity of separate nodes per deck makes adding EQ straightforward.