The modn parameter of SetSynth_Klatt is not used, so remove it.

src/libespeak-ng/klatt.c

 	return 0;
 }
 
-void SetSynth_Klatt(int length, int modn, frame_t *fr1, frame_t *fr2, voice_t *v, int control)
+void SetSynth_Klatt(int length, frame_t *fr1, frame_t *fr2, voice_t *v, int control)
 {
 	int ix;
 	DOUBLEX next;
 	}
 }
 
-int Wavegen_Klatt2(int length, int modulation, int resume, frame_t *fr1, frame_t *fr2)
+int Wavegen_Klatt2(int length, int resume, frame_t *fr1, frame_t *fr2)
 {
 	if (resume == 0)
-		SetSynth_Klatt(length, modulation, fr1, fr2, wvoice, 1);
+		SetSynth_Klatt(length, fr1, fr2, wvoice, 1);
 
 	return Wavegen_Klatt(resume);
 }

src/libespeak-ng/synthesize.h

 
 void KlattInit();
 void KlattReset(int control);
-int Wavegen_Klatt2(int length, int modulation, int resume, frame_t *fr1, frame_t *fr2);
+int Wavegen_Klatt2(int length, int resume, frame_t *fr1, frame_t *fr2);
 
 #ifdef __cplusplus
 }

src/libespeak-ng/wavegen.c

 			wdata.n_mix_wavefile = 0; // ... and drop through to WCMD_SPECT case
 		case WCMD_KLATT:
 			echo_complete = echo_length;
-			result = Wavegen_Klatt2(length & 0xffff, q[1] >> 16, resume, (frame_t *)q[2], (frame_t *)q[3]);
+			result = Wavegen_Klatt2(length & 0xffff, resume, (frame_t *)q[2], (frame_t *)q[3]);
 			break;
 #endif
 		case WCMD_MARKER: