Merge pull request #123 from Stability-AI/qk_layernorm

Add QK LayerNorm to transformer

stable_audio_tools/models/transformer.py

@@ -276,7 +276,7 @@ def __init__(
         dim_context = None,
         causal = False,
         zero_init_output=True,
-        qk_norm = False,
+        qk_norm: Literal['l2', 'ln', 'none'] = 'none',
         natten_kernel_size = None
     ):
         super().__init__()
@@ -302,6 +302,10 @@ def __init__(
 
         self.qk_norm = qk_norm
 
+        if self.qk_norm == "ln":
+            self.q_norm = nn.LayerNorm(dim_heads, elementwise_affine=True, eps=1.0e-6)
+            self.k_norm = nn.LayerNorm(dim_heads, elementwise_affine=True, eps=1.0e-6)
+
         # Using 1d neighborhood attention
         self.natten_kernel_size = natten_kernel_size
         if natten_kernel_size is not None:
@@ -416,9 +420,12 @@ def forward(
             q, k, v = map(lambda t: rearrange(t, 'b n (h d) -> b h n d', h = h), (q, k, v))
 
         # Normalize q and k for cosine sim attention
-        if self.qk_norm:
+        if self.qk_norm == "l2":
             q = F.normalize(q, dim=-1)
             k = F.normalize(k, dim=-1)
+        elif self.qk_norm == "ln":
+            q = self.q_norm(q)
+            k = self.k_norm(k)
 
         if rotary_pos_emb is not None and not has_context:
             freqs, _ = rotary_pos_emb