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Implements AF-Vocoder GAFilter (Interspeech 2025): learnable per-channel depthwise FIR filter inserted after each Snake/Activation1d in BigVGAN residual blocks. Initialized as identity so training starts from pretrained behaviour. - inject_gafilters() walks resblocks.*.activations and wraps each Activation1d with _ActivationWithGAFilter — weights appear in vocoder.state_dict() automatically - Trained alongside Snake alphas in snake_alpha_only mode - Checkpoint saves has_gafilter + gafilter_kernel_size metadata - Loader detects metadata and injects before load_state_dict so weights populate correctly - Controlled by use_gafilter (default True) and gafilter_kernel_size (default 9) Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>