╔═══════════════════════════════════════════════════════════════════════════════════════════════╗
║                  SPATIAL-BEATS TRAINING VS VALIDATION DATA FLOW                              ║
║                           (SHOWING THE ROOT CAUSES OF DOA GAP)                               ║
╚═══════════════════════════════════════════════════════════════════════════════════════════════╝

TRAINING PATH (epoch T)                            VALIDATION PATH (epoch T)
════════════════════════════════════════════════════════════════════════════════════════════════

┌─────────────────────────────────┐          ┌──────────────────────────────┐
│  FOA Waveform [4, T]            │          │  FOA Waveform [4, T]         │
│  (W, X, Y, Z channels)          │          │  (W, X, Y, Z channels)       │
└──────────────┬──────────────────┘          └────────────┬─────────────────┘
               │                                           │
               ▼ ─────────────────────────────────────────► ▼
        ╔══════════════════════╗                    ╔═══════════════════╗
        │  PREPROCESSING       │                    │ PREPROCESSING     │
        ├──────────────────────┤                    ├───────────────────┤
        │ • Normalize (same)   │                    │ • Normalize (same)│
        │ • Mel filterbank (OK)│                    │ • Mel filterbank  │
        │ • FOA features (OK)  │                    │   (OK)            │
        └──────────┬───────────┘                    └─────────┬─────────┘
                   │                                         │
    ⚠️ ISSUE #1 ◄──┘─────────────────────────────────────────┘ ⚠️ ISSUE #1
    
    SpecAugment:                           SpecAugment:
    ├─ freq_masks=2×27                     ├─ NO MASKING
    ├─ time_masks=2×100                    ├─ w_logmel unchanged
    └─ Applied to W channel                └─ Returns w_logmel as-is
    
    Result: ~20-50% of spec erased         Result: Full pristine spectrum
    
               │                                         │
               ▼ ─────────────────────────────────────────► ▼
        ╔══════════════════════╗                    ╔═══════════════════╗
        │  ENCODER (Frozen)    │                    │ ENCODER (Eval)    │
        │  • BEATs backbone    │                    │ • BEATs backbone  │
        │  • SpatialFuser      │                    │ • SpatialFuser    │
        │  • LocalSpatialEnc   │                    │ • LocalSpatialEnc │
        └──────────┬───────────┘                    └─────────┬─────────┘
                   │                                         │
               [B, T_s, D]                               [B, T_s, D]
               │                                         │
               ▼                                         ▼
        ╔══════════════════════╗                    ╔═══════════════════╗
        │ PREDICTION HEADS     │                    │ PREDICTION HEADS  │
        ├──────────────────────┤                    ├───────────────────┤
        │ activity_head        │                    │ activity_head     │
        │ class_head           │                    │ class_head        │
        │ direction_head       │                    │ direction_head    │
        │ distance_head        │                    │ distance_head     │
        └──────────┬───────────┘                    └─────────┬─────────┘
                   │                                         │
                   │ pred_activity [B, T_s, K]              │
                   │ pred_class    [B, T_s, K, C]           │
                   │ pred_dir      [B, T_s, K, 3]           │ (STALE in v10p1)
                   │ pred_dist     [B, T_s, K]              │
                   │                                         │
                   ▼                                         ▼
        ╔══════════════════════╗                    ╔═══════════════════╗
        │ HUNGARIAN MATCHING   │                    │ HUNGARIAN MATCHING│
        │ (per-frame)          │                    │ (per-frame)       │
        ├──────────────────────┤                    ├───────────────────┤
        │ For each (b, t):     │                    │ For each (b, t):  │
        │  cost = act_cost +   │                    │  cost = act_cost +│
        │         cls_nll +    │                    │         cls_nll + │
        │         dir_cost +   │                    │         dir_cost +│
        │         dist_cost    │                    │         dist_cost │
        │                      │                    │                   │
    ⚠️  │ ISSUE #4: Fixed cost │ ────────────────── │ ISSUE #4: But     │
        │ weights (1.0 each)   │ (v10p1: matches    │ loss uses lambda  │
        │ but loss uses        │  on stale DOA)     │ weights (0.0)     │
        │ variable lambda      │                    │                   │
        └──────────┬───────────┘                    └─────────┬─────────┘
                   │                                         │
               matched_slot                            matched_slot
               [B, N_gt, T_s]                         [B, N_gt, T_s]
               │                                         │
               ▼                                         ▼
        ╔══════════════════════╗                    ╔═══════════════════╗
        │ LOSS COMPUTATION     │                    │ METRICS COMPUTATION
        ├──────────────────────┤                    ├───────────────────┤
        │ loss_activity ×      │                    │ For matched pairs: │
        │   λ_frame_activity   │                    │  pred_azi_deg     │
        │ loss_class ×         │                    │  pred_ele_deg     │
        │   λ_frame_class      │                    │  tgt_azi_deg      │
        │ loss_direction × ◄─ v10p1: 0.0           │  tgt_ele_deg      │
        │   λ_frame_direction  │                    │                   │
        │ loss_distance × ◄─ v10p1: 0.0            │  azi_mae = MAE    │
        │   λ_frame_distance   │                    │  ele_mae = MAE    │
        └──────────┬───────────┘                    └─────────┬─────────┘
                   │                                         │
    ⚠️ ISSUE #2   │ v9:         Full training               │
    ────────────► │ v10 phase-1: FROZEN dir/dist head       │
                   │             no gradients!              │
                   │                                        │
                   ▼                                         ▼
            loss_total                            azi_mae, ele_mae
            (backprop)                           (forward only)


KEY ASYMMETRIES CAUSING TRAIN/VALID GAP
════════════════════════════════════════════════════════════════════════════════════════════════

┌─────────────────────────────────┬──────────────────────────┬──────────────┐
│ Aspect                          │ Training                 │ Validation   │
├─────────────────────────────────┼──────────────────────────┼──────────────┤
│ SpecAugment                     │ Masking 45% of spectrum  │ NO masking   │
│                                 │ →音频特性不同                           │
├─────────────────────────────────┼──────────────────────────┼──────────────┤
│ Spatial Augmentation (Rotation) │ NONE                     │ NONE         │
│                                 │ → DOA diversity limited  │ → Unseen     │
│                                 │   to ~1 epoch            │   angles     │
├─────────────────────────────────┼──────────────────────────┼──────────────┤
│ Direction Head State (v10p1)    │ FROZEN (no gradients)    │ FROZEN +     │
│                                 │ λ=0.0 (no loss signal)   │ STALE (from  │
│                                 │                          │   v9 epoch 3)│
├─────────────────────────────────┼──────────────────────────┼──────────────┤
│ Matching Cost Weights           │ Unweighted sum           │ Same unweighted
│                                 │ act + cls + dir + dist   │ sum, but on  │
│                                 │ (but loss uses lambda)   │ frozen DOA   │
├─────────────────────────────────┼──────────────────────────┼──────────────┤
│ Gradient Flow                   │ Through loss (v9) or     │ Validation   │
│                                 │ None (v10p1)             │ mode: no     │
│                                 │                          │ gradients    │
└─────────────────────────────────┴──────────────────────────┴──────────────┘


IMPACT CASCADE (Most Severe Scenario: ov3, v10 Phase-1)
════════════════════════════════════════════════════════════════════════════════════════════════

1. Training sees only ~single orientation per azimuth per epoch
   No rotation aug → limited DOA diversity
   
   ├─→ Model sees: (azi=0°, ele=0°), (azi=1°, ele=1°), ...
   └─→ Model learns: limited generalization to unseen angles

2. Direction head frozen at v10 phase-1 start
   λ_frame_direction = 0.0 → no training signal
   freeze_frame_track_spatial_heads = True → no gradients
   
   ├─→ Head receives: ZERO gradients from loss
   ├─→ Head receives: ZERO gradients from backward pass
   └─→ Result: Output completely stale (from v9 epoch 3)

3. At validation: direction head outputs used to compute metrics
   But outputs are unchanged from 10 epochs ago
   And model hasn't learned ov2/ov3 multi-source DOA at all
   
   ├─→ Validation sees: unseen azimuth combos (not in training)
   ├─→ Validation sees: multi-source situations unfamiliar to frozen head
   └─→ Result: 20-30° azimuth errors

4. SpecAugment makes training acoustic features different
   Masking 45% of W channel during training
   Zero masking at validation
   
   └─→ Result: +2-5° additional error on top


FIX #1: Add Rotation Augmentation
════════════════════════════════════════════════════════════════════════════════════════════════

Current (BROKEN):
  FOA [W, X, Y, Z] → (no change) → Encoder → DOA predictor

Fixed (CORRECT):
  FOA [W, X, Y, Z] → Rotate(θ, φ, ψ) → [W', X', Y', Z'] 
                  → Encoder → DOA predictor
  
  Labels: (azi, ele, dist) → Rotate_targets(θ, φ, ψ) → (azi', ele', dist)
  
  Result: Same class, different DOA → model learns generalization


FIX #2: Make SpecAugment Train/Val Consistent
════════════════════════════════════════════════════════════════════════════════════════════════

Current (BROKEN):
  Training:   if self.training: apply_masking() ✓
  Validation: if not self.training: skip_masking() ✗ (mismatch!)

Fixed (OPTION A):
  Training:   No masking (simplified, possibly less robust)
  Validation: No masking (consistent)

Fixed (OPTION B):
  Training:   apply_masking() ✓
  Validation: apply_same_masking_with_fixed_seed() ✓ (consistent)


FIX #3: Don't Fully Freeze Direction Head (v10)
════════════════════════════════════════════════════════════════════════════════════════════════

Current v10 (BROKEN):
  λ_frame_direction = 0.0
  freeze_frame_track_spatial_heads = True
  → Head receives zero signal for 10 epochs

Fixed (BETTER):
  λ_frame_direction = 0.1 (not zero!)
  freeze_frame_track_spatial_heads = False
  → Head receives weak signal to fine-tune on multi-source
  → Prevents complete staleness at v10 unfreezing