GUI: try using FFTW for per-chan osc wave center

not reliable yet

extern/fftw/kernel/tensor8.c

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2003, 2007-14 Matteo Frigo
+ * Copyright (c) 2003, 2007-14 Massachusetts Institute of Technology
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ */
+
+
+#include "kernel/ifftw.h"
+
+void X(tensor_destroy2)(tensor *a, tensor *b)
+{
+     X(tensor_destroy)(a);
+     X(tensor_destroy)(b);
+}
+
+void X(tensor_destroy4)(tensor *a, tensor *b, tensor *c, tensor *d)
+{
+     X(tensor_destroy2)(a, b);
+     X(tensor_destroy2)(c, d);
+}