diff --git a/.gitignore b/.gitignore
index f2e1d895..c4e25230 100644
--- a/.gitignore
+++ b/.gitignore
@@ -64,6 +64,9 @@ tools/*.png
 tools/*.tiff
 
 Fonderie/*.o
+Fonderie/*.png
+Fonderie/*.pnm
 Fonderie/fonderie
 Fonderie/interpolator
+Fonderie/t
 
diff --git a/Fonderie/Makefile b/Fonderie/Makefile
index e72df859..39a77106 100644
--- a/Fonderie/Makefile
+++ b/Fonderie/Makefile
@@ -8,7 +8,12 @@ LIBS = ../libfloatimg.a -lpnglite -lm
 OBJS = fonctions.o sfx.o crapulator.o glitches.o metriques.o
 DEPS = fonctions.h crapulator.h metriques.h glitches.h
 
-all:	fonderie interpolator
+all:	fonderie interpolator t
+
+# ---------------------------------------------------------
+
+t:	t.c Makefile glitches.o
+	gcc ${COPT} $< glitches.o  ${LIBS} -lz -o $@
 
 # ---------------------------------------------------------
 
diff --git a/Fonderie/glitches.c b/Fonderie/glitches.c
index 9fca56b0..7640d3d7 100644
--- a/Fonderie/glitches.c
+++ b/Fonderie/glitches.c
@@ -117,6 +117,7 @@ int vertical_singlitch(FloatImg *picz, int xpos, float fval,
 						float omega, float phi)
 {
 int		y, x, w, h;
+double		dy;
 
 #if DEBUG_LEVEL
 fprintf(stderr, ">>> %s ( %p %d %f %f )\n", __func__, picz,
@@ -124,9 +125,13 @@ fprintf(stderr, ">>> %s ( %p %d %f %f )\n", __func__, picz,
 #endif
 
 h = picz->height;		w = picz->width;
-#define BB 12
+#define BB 10
 for (y=BB; y<h-BB; y++) {
-	x = xpos;	/* add sinus deviation here */
+
+	dy = (double)y * omega;
+
+	x = xpos + (int)(10.9*sin(dy+phi));	/* add sinus deviation */
+
 	/* compute bounding box */
 	if ( (x>BB) && (x<w-BB) ) {
 		/* an make the glitch */
diff --git a/Fonderie/interpolator.c b/Fonderie/interpolator.c
index aa6172ac..273e1206 100644
--- a/Fonderie/interpolator.c
+++ b/Fonderie/interpolator.c
@@ -167,7 +167,7 @@ for (idx=0; idx<globbuf.gl_pathc; idx++) {
 		coef = (float)step / (float)Nsteps;
 		fimg_interpolate(pSecond, pFirst, &Out, coef);
 
-		/* here we can insert the output filter */
+		/* here we can insert the OUTPUT filter */
 		foo = crapulator(&Out, outfx, value);
 		if (foo) {
 			fprintf(stderr, "\nout fx %d crapulator failure %d\n",
diff --git a/Fonderie/t.c b/Fonderie/t.c
new file mode 100644
index 00000000..fafcb0b7
--- /dev/null
+++ b/Fonderie/t.c
@@ -0,0 +1,65 @@
+/*
+ * 		test des trucs
+ */
+
+#include  <stdio.h>
+#include  <stdlib.h>
+
+#include  "../floatimg.h"
+#include  "glitches.h"
+
+/* ----------------------------------------------------------- */
+
+int		verbosity;
+
+#define		PNG	"out.png"
+#define		W	512
+#define		H	256
+#define		LMAX	233.333
+#define		TIMER	1
+
+int main(int argc, char *argv[])
+{
+int		foo, iter, xloc, bloub;
+FloatImg	image;
+char		buff[1000];
+double		debut, fin;
+float		omega;
+verbosity = 1;
+
+fimg_print_version(1);
+
+foo = fimg_create(&image, W, H, FIMG_TYPE_RGB);
+if (foo) {
+	fprintf(stderr, "err %d create image\n", foo);
+	exit(1);
+	}
+fimg_vdeg_a(&image, LMAX);
+
+debut = fimg_timer_set(TIMER);
+
+for (iter=0; iter<64; iter++) {
+
+	for (bloub=0; bloub<5; bloub++) {
+		xloc = rand() % W;
+		omega = (float)(0.1 + drand48()*0.8) * 0.5;
+		foo = vertical_singlitch(&image, xloc, LMAX,
+						omega, (float)iter);
+		if (foo) abort();
+		}
+
+	sprintf(buff, "out%03d.png", iter);
+	foo = fimg_save_as_png(&image, buff, 0);
+	if (foo) {
+		fprintf(stderr, "err %d saving to '%s'\n", foo, PNG);
+		exit(1);
+		}
+	}
+
+fin = fimg_timer_set(TIMER);
+fprintf(stderr, "elapsed %f\n", fin-debut);
+
+return 0;
+}
+
+/* ----------------------------------------------------------- */
diff --git a/doc/the_floatimg_hack.tex b/doc/the_floatimg_hack.tex
index 313bb24b..8fcfbe56 100644
--- a/doc/the_floatimg_hack.tex
+++ b/doc/the_floatimg_hack.tex
@@ -694,7 +694,15 @@ int fimg_killcolors_b(FloatImg *fimg, float fval);
 int fimg_colors_mixer_a(FloatImg *fimg, float fval);
 \end{lstlisting}
 
+\subsection{Glitches}\index{glitch}
 
+Un \textsl{glitch} peut-il être classé dans la catégorie des effets
+spéciaux ou non ? \textsc{Hmha}, non. un fx est paramétrable
+et surtout répétitif. Un glitch est quasiment souvbent un phénomène
+aléatoire\index{drand48} et tout aussi paramétrable.
+
+J'ai commencé à étudier ces objets étranges quand j'ai commencé
+sur l'interpolator\index{interpolator} à l'automne 2020.
 
 %		----------------------------------