diff --git a/Fonderie/filterstack.c b/Fonderie/filterstack.c
index 13d9f71..0256436 100644
--- a/Fonderie/filterstack.c
+++ b/Fonderie/filterstack.c
@@ -105,6 +105,11 @@ if (numid < 0 || numid > NUMBER_OF_STACK) {
 	exit(1);
 	}
 
+if (0==f_stacks[numid].count) {
+	fprintf(stderr, "%s: stack %d empty ?\n", __func__, numid);
+	return -11;
+	}
+
 for (idx=0; idx<f_stacks[numid].count; idx++) {
 
 	eff = f_stacks[numid].slots[idx].numero;
diff --git a/Fonderie/interpolator.c b/Fonderie/interpolator.c
index 85bb3dd..83b70a0 100644
--- a/Fonderie/interpolator.c
+++ b/Fonderie/interpolator.c
@@ -163,7 +163,13 @@ for (idx=0; idx<globbuf.gl_pathc; idx++) {
 	value = idx_values[idx].value;
 
 	/* here, insert the input filter */
-	foo = crapulator(&B, infx, value);
+	if (infx) {
+		foo = crapulator(&B, infx, value);
+		}
+	else	{
+		foo = filterstack_run(0, &B, 0);
+		}
+
 	if (foo) {
 		fprintf(stderr, "%s: input fx fail %d\n", __func__, foo);
 		exit(1);
@@ -181,9 +187,9 @@ for (idx=0; idx<globbuf.gl_pathc; idx++) {
 		//	exit(1);
 		//	}
 
-		foo = filterstack_run(0, &Out, 0);
+		foo = filterstack_run(1, &Out, 0);
 		if (foo) {
-			fprintf(stderr, "run filt stk--> %d\n", foo);
+			fprintf(stderr, "run filt stack--> %d\n", foo);
 			return foo;
 			}
 
@@ -282,7 +288,12 @@ if (foo) {
 	exit(1);
 	}
 
-// filterstack_list(__FILE__);
+if (verbosity) {
+	puts("==============");
+	filterstack_list(0, __FILE__);
+	filterstack_list(1, __FILE__);
+	puts("==============");
+	}
 
 nbrsteps = atoi(argv[optind+2]);
 foo = interpolator(argv[optind], argv[optind+1], nbrsteps,