dhvani-v7

Dhvani v7: Decorrelated Multi-Head Embeddings

Dhvani v7 fixes the critical surface↔abhida head collapse in v6 (ρ=0.985 → -0.009) using hinge-based cross-covariance decorrelation. The three heads now produce genuinely independent embedding subspaces.

Key Results

Architecture

Input → Qwen3-1.7B (LoRA r=16, α=32) → Mean Pool (2048)
    → Shared Trunk (Linear 2048→1024 + LN + GELU)
        → Surface Head (Linear 1024→512 + LN)   — lexical/syntactic similarity
        → Abhida Head (Linear 1024→512 + LN)    — deep meaning (decorrelated from surface)
        → Vyanjana Head (Linear 1024→512 + LN)  — register/tone
    All heads → L2 normalized

The Decorrelation Fix

v6 trained with a weak orthogonality penalty (weight=0.1, dot-product only) → heads collapsed.

v7 uses hinge-based cross-covariance decorrelation:

• Full cross-covariance matrix penalty between surface↔abhida
• Hinge threshold (0.05): no gradient when already decorrelated → stable convergence
• Only applied to the collapsed pair; vyanjana was already independent
• VICReg-style variance regularization prevents dimensional collapse

Training

• Backbone: Qwen/Qwen3-1.7B with LoRA (r=16, α=32, targets: q/k/v/o_proj)
• Data: NLI (SNLI + MultiNLI) for surface/abhida + balanced style pairs for vyanjana
• Losses: InfoNCE (surface), hard-negative InfoNCE (abhida), register-contrastive (vyanjana), hinge cross-covariance
• Hardware: AWS g5.xlarge (A10G 24GB), 2500 steps, ~3.5h
• Optimizer: AdamW (lr=1e-4, cosine schedule, 500-step warmup)

Checkpoint Format

{
    'step': 2500,
    'config': {...},
    'metrics': {'cos_surf_abhi': -0.009, 'sts17_surface': 0.883, ...},
    'lora': model.base.state_dict(),
    'trunk': model.trunk.state_dict(),
    'surface_head': model.surface_head.state_dict(),
    'abhida_head': model.abhida_head.state_dict(),
    'vyanjana_head': model.vyanjana_head.state_dict(),
    'optimizer': ...,
    'scheduler': ...,
}

Usage

import torch
import torch.nn as nn
import torch.nn.functional as F
from transformers import AutoModel, AutoTokenizer
from peft import get_peft_model, LoraConfig, TaskType
from huggingface_hub import hf_hub_download

class DhvaniV7(nn.Module):
    def __init__(self, cfg):
        super().__init__()
        base = AutoModel.from_pretrained(
            cfg['base_model'], torch_dtype=torch.bfloat16,
            attn_implementation='eager', trust_remote_code=True
        )
        lora_config = LoraConfig(
            r=cfg['lora_r'], lora_alpha=cfg['lora_alpha'],
            lora_dropout=cfg['lora_dropout'],
            target_modules=cfg['lora_targets'],
            bias='none', task_type=TaskType.FEATURE_EXTRACTION
        )
        self.base = get_peft_model(base, lora_config)
        self.trunk = nn.Sequential(
            nn.Linear(cfg['hidden_dim'], cfg['trunk_dim']),
            nn.LayerNorm(cfg['trunk_dim']), nn.GELU(),
        )
        self.surface_head = nn.Sequential(
            nn.Linear(cfg['trunk_dim'], cfg['subspace_dim']),
            nn.LayerNorm(cfg['subspace_dim']),
        )
        self.abhida_head = nn.Sequential(
            nn.Linear(cfg['trunk_dim'], cfg['subspace_dim']),
            nn.LayerNorm(cfg['subspace_dim']),
        )
        self.vyanjana_head = nn.Sequential(
            nn.Linear(cfg['trunk_dim'], cfg['subspace_dim']),
            nn.LayerNorm(cfg['subspace_dim']),
        )

    @staticmethod
    def mean_pool(hidden, mask):
        m = mask.unsqueeze(-1).float()
        return (hidden * m).sum(1) / m.sum(1).clamp(min=1e-9)

    def encode_tokens(self, input_ids, attention_mask):
        out = self.base(input_ids=input_ids, attention_mask=attention_mask)
        pooled = self.mean_pool(out.last_hidden_state.float(), attention_mask)
        trunk = self.trunk(pooled)
        return {
            'surface': F.normalize(self.surface_head(trunk), p=2, dim=-1),
            'abhida': F.normalize(self.abhida_head(trunk), p=2, dim=-1),
            'vyanjana': F.normalize(self.vyanjana_head(trunk), p=2, dim=-1),
            'full': F.normalize(torch.cat([
                self.surface_head(trunk),
                self.abhida_head(trunk),
                self.vyanjana_head(trunk),
            ], dim=-1), p=2, dim=-1),
        }

# Load
ckpt_path = hf_hub_download(repo_id="rb512/dhvani-v7", filename="v7_best.pt")
ckpt = torch.load(ckpt_path, map_location="cpu", weights_only=False)
cfg = ckpt["config"]

tokenizer = AutoTokenizer.from_pretrained(cfg['base_model'], trust_remote_code=True)
if tokenizer.pad_token is None:
    tokenizer.pad_token = tokenizer.eos_token

model = DhvaniV7(cfg)
model.base.load_state_dict(ckpt["lora"])
model.trunk.load_state_dict(ckpt["trunk"])
model.surface_head.load_state_dict(ckpt["surface_head"])
model.abhida_head.load_state_dict(ckpt["abhida_head"])
model.vyanjana_head.load_state_dict(ckpt["vyanjana_head"])
model.eval()

# Encode
texts = ["The cat sat on the mat.", "A feline rested upon the rug."]
enc = tokenizer(texts, max_length=128, truncation=True, padding='max_length', return_tensors='pt')
with torch.no_grad():
    embs = model.encode_tokens(enc['input_ids'], enc['attention_mask'])

# Surface: high similarity (paraphrases)
# Abhida: high similarity (same meaning, decorrelated from surface)
# Vyanjana: similar (same register)
print(f"Surface sim: {(embs['surface'][0] @ embs['surface'][1]).item():.3f}")
print(f"Abhida sim:  {(embs['abhida'][0] @ embs['abhida'][1]).item():.3f}")
print(f"Vyanjana sim: {(embs['vyanjana'][0] @ embs['vyanjana'][1]).item():.3f}")

Philosophical Inspiration

Named after Ānandavardhana's 9th-century theory of dhvani (resonance) in Sanskrit poetics:

• Abhidā (अभिधा, denotation): literal propositional content — what was said
• Vyañjanā (व्यञ्जना, suggestion): expressive register and style — how it was said
• Surface: overall graded semantic similarity

Related

• Karaka Attention: Uses abhida head as conditioning signal for semantically typed attention
• AGT: Action-Gating Test (Springer AI & Ethics)

Citation

@article{dhvani2026,
  title={Dhvani: Structured Multi-Head Embeddings that Separate What Was Said from How It Was Said},
  author={Baxi, Rahul},
  year={2026},
  note={VyasaLabs Technical Report}
}

License

Apache 2.0