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Adding some comments

--- a/dnn/fwgan.c

+++ b/dnn/fwgan.c

@@ -105,8 +105,12 @@

   st->embed_phase[0] = 1;

   model = &st->model;

   compute_wlpc(lpc, features0);

+  /* Deemphasis memory is just the last continuation sample. */

   st->deemph_mem = pcm0[CONT_PCM_INPUTS-1];

+  /* Apply analysis filter, considering that the preemphasis and deemphasis filter

+     cancel each other in this case since the LPC filter is constant across that boundary.

+     */

   for (i=LPC_ORDER;i<CONT_PCM_INPUTS;i++) {

     int j;

     wpcm0[i] = pcm0[i];

@@ -115,7 +119,10 @@

   /* FIXME: Make this less stupid. */

   for (i=0;i<LPC_ORDER;i++) wpcm0[i] = wpcm0[LPC_ORDER];

+  /* The memory of the pre-empahsis is the last sample of the weighted signal

+     (ignoring preemphasis+deemphasis combination). */

   st->preemph_mem = wpcm0[CONT_PCM_INPUTS-1];

+  /* The memory of the synthesis filter is the pre-emphasized continuation. */

   for (i=0;i<LPC_ORDER;i++) st->syn_mem[i] = pcm0[CONT_PCM_INPUTS-1-i] - FWGAN_DEEMPHASIS*pcm0[CONT_PCM_INPUTS-2-i];

   norm2 = celt_inner_prod(wpcm0, wpcm0, CONT_PCM_INPUTS, st->arch);

@@ -123,6 +130,7 @@

   for (i=0;i<CONT_PCM_INPUTS;i++) cont_inputs[i+1] = norm_1*wpcm0[i];

   cont_inputs[0] = log(sqrt(norm2) + 1e-7f);

+  /* Continuation network */

   compute_generic_dense(&model->cont_net_0, tmp1, cont_inputs, ACTIVATION_TANH);

   compute_generic_dense(&model->cont_net_2, tmp2, tmp1, ACTIVATION_TANH);

   compute_generic_dense(&model->cont_net_4, tmp1, tmp2, ACTIVATION_TANH);

@@ -131,6 +139,7 @@

   celt_assert(CONT_NET_10_OUT_SIZE == model->cont_net_10.nb_outputs);

   compute_generic_dense(&model->cont_net_10, st->cont, tmp1, ACTIVATION_TANH);

+  /* Computing continuation for each layer. */

   celt_assert(RNN_GRU_STATE_SIZE == model->rnn_cont_fc_0.nb_outputs);

   compute_generic_dense(&model->rnn_cont_fc_0, st->rnn_state, st->cont, ACTIVATION_TANH);

@@ -150,6 +159,8 @@

   compute_generic_dense(&model->fwc7_cont_fc_0, st->fwc7_state, st->cont, ACTIVATION_TANH);

   st->cont_initialized = 1;

+  /* Process the first frame, discard the first subframe, and keep the rest for the first

+     synthesis call. */

   fwgan_synthesize_impl(st, new_pcm, lpc, features0);

   OPUS_COPY(st->pcm_buf, &new_pcm[SUBFRAME_SIZE], FWGAN_FRAME_SIZE-SUBFRAME_SIZE);

 }

@@ -209,6 +220,8 @@

   compute_gated_activation(&model->feat_in_nl1_gate, rnn_in, rnn_in, ACTIVATION_TANH);

   if (st->cont_initialized == 1) {

+    /* On the very first subframe we stop here. We only want to run the feat_in layer since the

+       others are initialized via the continuation network. */

     OPUS_CLEAR(pcm, SUBFRAME_SIZE);

     st->cont_initialized = 2;

     apply_gain(pcm, c0, &st->last_gain);

@@ -247,8 +260,6 @@

   fwgan_deemphasis(pcm, &st->deemph_mem);

 }

-

-

 void fwgan_init(FWGANState *st)

 {

   int ret;

@@ -285,6 +296,7 @@

   float new_pcm[FWGAN_FRAME_SIZE];

   compute_wlpc(lpc, features);

   fwgan_synthesize_impl(st, new_pcm, lpc, features);

+  /* Handle buffering. */

   OPUS_COPY(pcm, st->pcm_buf, FWGAN_FRAME_SIZE-SUBFRAME_SIZE);

   OPUS_COPY(&pcm[FWGAN_FRAME_SIZE-SUBFRAME_SIZE], new_pcm, SUBFRAME_SIZE);

   OPUS_COPY(st->pcm_buf, &new_pcm[SUBFRAME_SIZE], FWGAN_FRAME_SIZE-SUBFRAME_SIZE);

-- 

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