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Prevents a folding artefact due to "folding the folding"

--- a/libcelt/bands.c

+++ b/libcelt/bands.c

@@ -927,6 +927,7 @@

       int b;

       int N;

       int curr_balance;

+      celt_norm *effective_lowband=NULL;

       celt_norm * restrict X, * restrict Y;

       int tf_change=0;

@@ -962,7 +963,7 @@

          b = C*16*N<<BITRES;

       if (M*eBands[i]-N >= M*eBands[start] && (update_lowband || lowband==NULL))

-            lowband = norm+M*eBands[i]-N;

+            lowband = norm+M*eBands[i];

       tf_change = tf_res[i];

       if (i>=m->effEBands)

@@ -972,8 +973,15 @@

             Y = norm;

       }

+      /* This ensures we never repeat spectral content within one band */

+      if (lowband != NULL)

+      {

+         effective_lowband = lowband-N;

+         if (effective_lowband < norm+M*eBands[start])

+            effective_lowband = norm+M*eBands[start];

+      }

       quant_band(encode, m, i, X, Y, N, b, fold, B, tf_change,

-            lowband, resynth, ec, &remaining_bits, LM,

+            effective_lowband, resynth, ec, &remaining_bits, LM,

             norm+M*eBands[i], bandE, 0, &seed, Q15ONE, lowband_scratch);

       balance += pulses[i] + tell;