diff --git a/lib_com/cnst.h b/lib_com/cnst.h
index a2d051d876401b0d4c1e46d46e442dac5c38de96..17dbc31c4392fce7232ba2c2040e7ebad91abe9d 100644
--- a/lib_com/cnst.h
+++ b/lib_com/cnst.h
@@ -45,20 +45,22 @@
 #define MATRIX_CONSTANT (759250113) 
 #define NUM_SAMPLES_960 (960)
 #define NUM_SAMPLES_720 (720)
+#define NUM_SAMPLES_640 (640)
 #define NUM_SAMPLES_320 (320)
 #define NUM_SAMPLES_160 (160)
 #define L_SUBFRAME_48k         (240)
 #define L_SUBFRAME_32k         (180)
 #define L_SUBFRAME_16k         (80)
 #define L_SUBFRAME_8k           (40)
-#define Q31_BY_NUM_SAMPLES_960 ( 2239294 )
-#define Q31_BY_NUM_SAMPLES_720 ( 2986764 )
-#define Q31_BY_NUM_SAMPLES_320 ( 6731924 )
-#define Q31_BY_NUM_SAMPLES_160 ( 13506186 )
-#define Q31_BY_SUB_FRAME_240 ( 8985287 )
-#define Q31_BY_SUB_FRAME_180 ( 11997115 )
-#define Q31_BY_SUB_FRAME_80  ( 27183337 )
-#define Q31_BY_SUB_FRAME_40  ( 55063683 )
+#define Q31_BY_NUM_SAMPLES_960 ( 2239294 ) /* 1/959 in Q31 */
+#define Q31_BY_NUM_SAMPLES_720 ( 2986764 ) /* 1/719 in Q31 */
+#define Q31_BY_NUM_SAMPLES_640 ( 3360694 ) /* 1/639 in Q31 */
+#define Q31_BY_NUM_SAMPLES_320 ( 6731924 ) /* 1/319 in Q31 */
+#define Q31_BY_NUM_SAMPLES_160 ( 13506186 ) /* 1/159 in Q31 */
+#define Q31_BY_SUB_FRAME_240 ( 8985287 ) /* 1/239 in Q31 */
+#define Q31_BY_SUB_FRAME_180 ( 11997115 ) /* 1/179 in Q31 */
+#define Q31_BY_SUB_FRAME_80  ( 27183337 ) /* 1/79 in Q31 */
+#define Q31_BY_SUB_FRAME_40  ( 55063683 ) /* 1/39 in Q31 */
 
 
 /*----------------------------------------------------------------------------------*
diff --git a/lib_rend/lib_rend_fx.c b/lib_rend/lib_rend_fx.c
index e39b9a61e5e69fad68e535a1ef6ce72e23023fe8..2b70c2e21086b71248f8795522827a8e75780584 100644
--- a/lib_rend/lib_rend_fx.c
+++ b/lib_rend/lib_rend_fx.c
@@ -4579,6 +4579,12 @@ static void renderBufferChannelLerp_fx(
                         move32();
                         move32();
                         BREAK;
+                    case NUM_SAMPLES_640:
+                        tmp = Q31_BY_NUM_SAMPLES_640;
+                        tmp1 = 639; /* NUM_SAMPLES_640 - 1 */
+                        move32();
+                        move32();
+                        BREAK;
                     case NUM_SAMPLES_320:
                         tmp = Q31_BY_NUM_SAMPLES_320;
                         tmp1 = 319; /* NUM_SAMPLES_320 - 1 */