diff --git a/src/owl/fftpack/owl_fft_d.mli b/src/owl/fftpack/owl_fft_d.mli
index 093791d42..ea80f18bb 100644
--- a/src/owl/fftpack/owl_fft_d.mli
+++ b/src/owl/fftpack/owl_fft_d.mli
@@ -5,24 +5,25 @@
 
 open Bigarray
 open Owl_dense_ndarray_generic
+open Owl_fft_generic
 
 val fft
   :  ?axis:int
-  -> ?norm:int
+  -> ?norm:tnorm
   -> ?nthreads:int
   -> (Complex.t, complex64_elt) Owl_dense_ndarray_generic.t
   -> (Complex.t, complex64_elt) Owl_dense_ndarray_generic.t
 
 val ifft
   :  ?axis:int
-  -> ?norm:int
+  -> ?norm:tnorm
   -> ?nthreads:int
   -> (Complex.t, complex64_elt) Owl_dense_ndarray_generic.t
   -> (Complex.t, complex64_elt) Owl_dense_ndarray_generic.t
 
 val rfft
   :  ?axis:int
-  -> ?norm:int
+  -> ?norm:tnorm
   -> ?nthreads:int
   -> (float, float64_elt) t
   -> (Complex.t, complex64_elt) t
@@ -30,7 +31,7 @@ val rfft
 val irfft
   :  ?axis:int
   -> ?n:int
-  -> ?norm:int
+  -> ?norm:tnorm
   -> ?nthreads:int
   -> (Complex.t, complex64_elt) t
   -> (float, float64_elt) t
@@ -41,8 +42,8 @@ val ifft2 : (Complex.t, complex64_elt) t -> (Complex.t, complex64_elt) t
 
 val dct
   :  ?axis:int
-  -> ?ttype:int
-  -> ?norm:int
+  -> ?ttype:ttrig_transform
+  -> ?norm:tnorm
   -> ?ortho:bool
   -> ?nthreads:int
   -> (float, float64_elt) t
@@ -50,8 +51,8 @@ val dct
 
 val idct
   :  ?axis:int
-  -> ?ttype:int
-  -> ?norm:int
+  -> ?ttype:ttrig_transform
+  -> ?norm:tnorm
   -> ?ortho:bool
   -> ?nthreads:int
   -> (float, float64_elt) t
@@ -59,8 +60,8 @@ val idct
 
 val dst
   :  ?axis:int
-  -> ?ttype:int
-  -> ?norm:int
+  -> ?ttype:ttrig_transform
+  -> ?norm:tnorm
   -> ?ortho:bool
   -> ?nthreads:int
   -> (float, float64_elt) t
@@ -68,8 +69,8 @@ val dst
 
 val idst
   :  ?axis:int
-  -> ?ttype:int
-  -> ?norm:int
+  -> ?ttype:ttrig_transform
+  -> ?norm:tnorm
   -> ?ortho:bool
   -> ?nthreads:int
   -> (float, float64_elt) t
diff --git a/src/owl/fftpack/owl_fft_generic.ml b/src/owl/fftpack/owl_fft_generic.ml
index 4d24c219c..377e7a0c7 100644
--- a/src/owl/fftpack/owl_fft_generic.ml
+++ b/src/owl/fftpack/owl_fft_generic.ml
@@ -5,7 +5,17 @@
 
 open Owl_dense_ndarray_generic
 
-let fft ?axis ?(norm : int = 0) ?(nthreads : int = 1) x =
+type tnorm =
+  | Backward
+  | Forward
+  | Ortho
+
+let tnorm_to_int = function
+  | Backward -> 0
+  | Forward -> 1
+  | Ortho -> 2
+
+let fft ?axis ?(norm : tnorm = Backward) ?(nthreads : int = 1) x =
   let axis =
     match axis with
     | Some a -> a
@@ -14,11 +24,11 @@ let fft ?axis ?(norm : int = 0) ?(nthreads : int = 1) x =
   let axis = if axis < 0 then num_dims x + axis else axis in
   assert (axis < num_dims x);
   let y = empty (kind x) (shape x) in
-  Owl_fftpack._owl_cfftf (kind x) x y axis norm nthreads;
+  Owl_fftpack._owl_cfftf (kind x) x y axis (tnorm_to_int norm) nthreads;
   y
 
 
-let ifft ?axis ?(norm : int = 1) ?(nthreads : int = 1) x =
+let ifft ?axis ?(norm : tnorm = Forward) ?(nthreads : int = 1) x =
   let axis =
     match axis with
     | Some a -> a
@@ -27,11 +37,11 @@ let ifft ?axis ?(norm : int = 1) ?(nthreads : int = 1) x =
   let axis = if axis < 0 then num_dims x + axis else axis in
   assert (axis < num_dims x);
   let y = empty (kind x) (shape x) in
-  Owl_fftpack._owl_cfftb (kind x) x y axis norm nthreads;
+  Owl_fftpack._owl_cfftb (kind x) x y axis (tnorm_to_int norm) nthreads;
   y
 
 
-let rfft ?axis ?(norm : int = 0) ?(nthreads : int = 1) ~(otyp : ('a, 'b) kind) x =
+let rfft ?axis ?(norm : tnorm = Backward) ?(nthreads : int = 1) ~(otyp : ('a, 'b) kind) x =
   let axis =
     match axis with
     | Some a -> a
@@ -43,11 +53,11 @@ let rfft ?axis ?(norm : int = 0) ?(nthreads : int = 1) ~(otyp : ('a, 'b) kind) x
   s.(axis) <- (s.(axis) / 2) + 1;
   let y = empty otyp s in
   let ityp = kind x in
-  Owl_fftpack._owl_rfftf ityp otyp x y axis norm nthreads;
+  Owl_fftpack._owl_rfftf ityp otyp x y axis (tnorm_to_int norm) nthreads;
   y
 
 
-let irfft ?axis ?n ?(norm : int = 1) ?(nthreads : int = 1) ~(otyp : ('a, 'b) kind) x =
+let irfft ?axis ?n ?(norm : tnorm = Forward) ?(nthreads : int = 1) ~(otyp : ('a, 'b) kind) x =
   let axis =
     match axis with
     | Some a -> a
@@ -63,7 +73,7 @@ let irfft ?axis ?n ?(norm : int = 1) ?(nthreads : int = 1) ~(otyp : ('a, 'b) kin
   in
   let y = empty otyp s in
   let ityp = kind x in
-  Owl_fftpack._owl_rfftb ityp otyp x y axis norm nthreads;
+  Owl_fftpack._owl_rfftb ityp otyp x y axis (tnorm_to_int norm) nthreads;
   y
 
 
@@ -71,7 +81,19 @@ let fft2 x = fft ~axis:0 x |> fft ~axis:1
 
 let ifft2 x = ifft ~axis:0 x |> ifft ~axis:1
 
-let dct ?axis ?(ttype = 2) ?(norm : int = 0) ?(ortho : bool option) ?(nthreads = 1) x =
+type ttrig_transform  =
+  | I
+  | II
+  | III
+  | IV
+
+let ttrig_transform_to_int = function
+  | I -> 1
+  | II -> 2
+  | III -> 3
+  | IV -> 4
+
+let dct ?axis ?(ttype: ttrig_transform = II) ?(norm : tnorm = Backward) ?(ortho : bool option) ?(nthreads = 1) x =
   let axis =
     match axis with
     | Some a -> a
@@ -82,15 +104,14 @@ let dct ?axis ?(ttype = 2) ?(norm : int = 0) ?(ortho : bool option) ?(nthreads =
   let ortho =
     match ortho with
     | Some o -> o
-    | None -> if norm = 2 then true else false
+    | None -> if norm = Ortho then true else false
   in
-  assert (ttype > 0 || ttype < 5);
   let y = empty (kind x) (shape x) in
-  Owl_fftpack._owl_dctf (kind x) x y axis ttype norm ortho nthreads;
+  Owl_fftpack._owl_dctf (kind x) x y axis (ttrig_transform_to_int ttype) (tnorm_to_int norm) ortho nthreads;
   y
 
 
-let idct ?axis ?(ttype = 3) ?(norm : int = 1) ?(ortho : bool option) ?(nthreads = 1) x =
+let idct ?axis ?(ttype: ttrig_transform = II) ?(norm : tnorm = Forward) ?(ortho : bool option) ?(nthreads = 1) x =
   let axis =
     match axis with
     | Some a -> a
@@ -101,15 +122,14 @@ let idct ?axis ?(ttype = 3) ?(norm : int = 1) ?(ortho : bool option) ?(nthreads
   let ortho =
     match ortho with
     | Some o -> o
-    | None -> if norm = 2 then true else false
+    | None -> if norm = Ortho then true else false
   in
-  assert (ttype > 0 || ttype < 5);
   let y = empty (kind x) (shape x) in
-  Owl_fftpack._owl_dctb (kind x) x y axis ttype norm ortho nthreads;
+  Owl_fftpack._owl_dctb (kind x) x y axis (ttrig_transform_to_int ttype) (tnorm_to_int norm) ortho nthreads;
   y
 
 
-let dst ?axis ?(ttype = 2) ?(norm : int = 0) ?(ortho : bool option) ?(nthreads = 1) x =
+let dst ?axis ?(ttype: ttrig_transform = II) ?(norm : tnorm = Backward) ?(ortho : bool option) ?(nthreads = 1) x =
   let axis =
     match axis with
     | Some a -> a
@@ -120,15 +140,14 @@ let dst ?axis ?(ttype = 2) ?(norm : int = 0) ?(ortho : bool option) ?(nthreads =
   let ortho =
     match ortho with
     | Some o -> o
-    | None -> if norm = 2 then true else false
+    | None -> if norm = Ortho then true else false
   in
-  assert (ttype > 0 || ttype < 5);
   let y = empty (kind x) (shape x) in
-  Owl_fftpack._owl_dstf (kind x) x y axis ttype norm ortho nthreads;
+  Owl_fftpack._owl_dstf (kind x) x y axis (ttrig_transform_to_int ttype) (tnorm_to_int norm) ortho nthreads;
   y
 
 
-let idst ?axis ?(ttype = 3) ?(norm : int = 1) ?(ortho : bool option) ?(nthreads = 1) x =
+let idst ?axis ?(ttype = III) ?(norm : tnorm = Forward) ?(ortho : bool option) ?(nthreads = 1) x =
   let axis =
     match axis with
     | Some a -> a
@@ -139,9 +158,8 @@ let idst ?axis ?(ttype = 3) ?(norm : int = 1) ?(ortho : bool option) ?(nthreads
   let ortho =
     match ortho with
     | Some o -> o
-    | None -> if norm = 2 then true else false
+    | None -> if norm = Ortho then true else false
   in
-  assert (ttype > 0 || ttype < 5);
   let y = empty (kind x) (shape x) in
-  Owl_fftpack._owl_dstb (kind x) x y axis ttype norm ortho nthreads;
+  Owl_fftpack._owl_dstb (kind x) x y axis (ttrig_transform_to_int ttype) (tnorm_to_int norm) ortho nthreads;
   y
diff --git a/src/owl/fftpack/owl_fft_generic.mli b/src/owl/fftpack/owl_fft_generic.mli
index ef0d63032..d66528bc9 100644
--- a/src/owl/fftpack/owl_fft_generic.mli
+++ b/src/owl/fftpack/owl_fft_generic.mli
@@ -7,48 +7,59 @@
 
 open Owl_dense_ndarray_generic
 
+(** Normalisation options for transforms. *)
+type tnorm =
+  | Backward (** No normalization on Forward and scaling by 1/N on Backward *)
+  | Forward (** Normalization by 1/N on the Forward transform. *)
+  | Ortho (** Forward and Backward are scaled by 1/sqrt(N) *)
+
 (** {5 Discrete Fourier Transforms functions} *)
 
 val fft
   :  ?axis:int
-  -> ?norm:int
+  -> ?norm:tnorm
   -> ?nthreads:int
   -> (Complex.t, 'a) t
   -> (Complex.t, 'a) t
-(** [fft ~axis x] performs 1-dimensional FFT on a complex input. [axis] is the
-    highest dimension if not specified. The return is not scaled. *)
+(** [fft ~axis ~norm x] performs 1-dimensional FFT on a complex input. [axis] is the
+    highest dimension if not specified. [norm] is the normalization option. By default, [norm] is set to [Backward].
+    [nthreads] is the desired number of threads used to compute the fft. *)
 
 val ifft
   :  ?axis:int
-  -> ?norm:int
+  -> ?norm:tnorm
   -> ?nthreads:int
   -> (Complex.t, 'a) t
   -> (Complex.t, 'a) t
 (** [ifft ~axis x] performs inverse 1-dimensional FFT on a complex input. The parameter [axis]
-    indicates the highest dimension by default. *)
+    indicates the highest dimension by default. [norm] is the normalization option. By default, [norm] is set to [Forward].
+    [nthreads] is the desired number of threads used to compute the fft. *)
 
 val rfft
   :  ?axis:int
-  -> ?norm:int
+  -> ?norm:tnorm
   -> ?nthreads:int
   -> otyp:('a, 'b) kind
   -> ('c, 'd) t
   -> ('a, 'b) t
 (** [rfft ~axis ~otyp x] performs 1-dimensional FFT on real input along the
-    [axis]. [otyp] is used to specify the output type, it must be the consistent
-    precision with input [x]. You can skip this parameter by using a submodule
-    with specific precision such as [Owl.Fft.S] or [Owl.Fft.D]. *)
+    [axis]. [norm] is the normalization option. By default, [norm] is set to [Backward].
+    [nthreads] is the desired number of threads used to compute the fft.
+    [otyp] is used to specify the output type, it must be the consistent precision with input [x].
+    You can skip this parameter by using a submodule with specific precision such as [Owl.Fft.S] or [Owl.Fft.D]. *)
 
 val irfft
   :  ?axis:int
   -> ?n:int
-  -> ?norm:int
+  -> ?norm:tnorm
   -> ?nthreads:int
   -> otyp:('a, 'b) kind
   -> ('c, 'd) t
   -> ('a, 'b) t
-(** [irfft ~axis ~n x] is the inverse function of [rfft]. Note the [n] parameter
-    is used to specified the size of output. *)
+(** [irfft ~axis ~n x] is the inverse function of [rfft]. [norm] is the normalization option.
+    By default, [norm] is set to [Forward].
+    [nthreads] is the desired number of threads used to compute the fft.
+    Note the [n] parameter is used to specified the size of output. *)
 
 val fft2 : (Complex.t, 'a) t -> (Complex.t, 'a) t
 (** [fft2 x] performs 2-dimensional FFT on a complex input. The return is not scaled. *)
@@ -58,42 +69,61 @@ val ifft2 : (Complex.t, 'a) t -> (Complex.t, 'a) t
 
 (** {5 Discrete Cosine & Sine Transforms functions} *)
 
+type ttrig_transform  =
+  | I
+  | II
+  | III
+  | IV
+(** Trigonometric (Cosine and Sine) transform types. *)
+
 val dct
   :  ?axis:int
-  -> ?ttype:int
-  -> ?norm:int
+  -> ?ttype:ttrig_transform
+  -> ?norm:tnorm
   -> ?ortho:bool
   -> ?nthreads:int
   -> ('a, 'b) t
   -> ('a, 'b) t
-(** [dct ~axis ~type x] performs 1-dimensional Discrete Cosine Transform (DCT) on a real input. Default type is 2. *)
+(** [dct ?axis ?ttype ?norm ?ortho ?nthreads x] performs 1-dimensional Discrete Cosine Transform (DCT) on a real input.
+    [ttype] is the DCT type to use for this transform. Default value is [II].
+    [norm] is the normalization option. By default, [norm] is set to [Backward].
+    [ortho] constrols whether or not we should use the orthogonalized variant of the DCT. *)
 
 val idct
   :  ?axis:int
-  -> ?ttype:int
-  -> ?norm:int
+  -> ?ttype:ttrig_transform
+  -> ?norm:tnorm
   -> ?ortho:bool
   -> ?nthreads:int
   -> ('a, 'b) t
   -> ('a, 'b) t
-(** [idct ~axis ~type x] performs inverse 1-dimensional Discrete Cosine Transform (DCT) on a real input. Default type is 2. *)
+(** [idct ?axis ?ttype ?norm ?ortho ?nthreads x] performs inverse 1-dimensional Discrete Cosine Transform (DCT) on a real input.
+    [ttype] is the DCT type to use for this transform. Default value is [II].
+    [norm] is the normalization option. By default, [norm] is set to [Forward].
+    [ortho] constrols whether or not we should use the orthogonalized variant of the DCT. *)
 
 val dst
   :  ?axis:int
-  -> ?ttype:int
-  -> ?norm:int
+  -> ?ttype:ttrig_transform
+  -> ?norm:tnorm
   -> ?ortho:bool
   -> ?nthreads:int
   -> ('a, 'b) t
   -> ('a, 'b) t
-(** [dst ~axis ~type x] performs 1-dimensional Discrete Sine Transform (DST) on a real input. Default type is 2. *)
+(** [dst ?axis ?ttype ?norm ?ortho ?nthreads x] performs 1-dimensional Discrete Sine Transform (DCT) on a real input.
+    [ttype] is the DCT type to use for this transform. Default value is [II].
+    [norm] is the normalization option. By default, [norm] is set to [Backward].
+    [ortho] constrols whether or not we should use the orthogonalized variant of the DST. *)
 
 val idst
   :  ?axis:int
-  -> ?ttype:int
-  -> ?norm:int
+  -> ?ttype:ttrig_transform
+  -> ?norm:tnorm
   -> ?ortho:bool
   -> ?nthreads:int
   -> ('a, 'b) t
   -> ('a, 'b) t
-(** [idst ~axis ~type x] performs inverse 1-dimensional Discrete Sine Transform (DST) on a real input. Default type is 2. *)
+(** [idst ?axis ?ttype ?norm ?ortho ?nthreads x] performs inverse 1-dimensional Discrete Sine Transform (DST) on a real input.
+    [ttype] is the DST type to use for this transform. Default value is [II].
+    [norm] is the normalization option. By default, [norm] is set to [Forward].
+    [ortho] constrols whether or not we should use the orthogonalized variant of the DST. *)
\ No newline at end of file
diff --git a/src/owl/fftpack/owl_fft_s.mli b/src/owl/fftpack/owl_fft_s.mli
index aa4b0a643..3914d685c 100644
--- a/src/owl/fftpack/owl_fft_s.mli
+++ b/src/owl/fftpack/owl_fft_s.mli
@@ -5,24 +5,25 @@
 
 open Bigarray
 open Owl_dense_ndarray_generic
+open Owl_fft_generic
 
 val fft
   :  ?axis:int
-  -> ?norm:int
+  -> ?norm:tnorm
   -> ?nthreads:int
   -> (Complex.t, complex32_elt) Owl_dense_ndarray_generic.t
   -> (Complex.t, complex32_elt) Owl_dense_ndarray_generic.t
 
 val ifft
   :  ?axis:int
-  -> ?norm:int
+  -> ?norm:tnorm
   -> ?nthreads:int
   -> (Complex.t, complex32_elt) Owl_dense_ndarray_generic.t
   -> (Complex.t, complex32_elt) Owl_dense_ndarray_generic.t
 
 val rfft
   :  ?axis:int
-  -> ?norm:int
+  -> ?norm:tnorm
   -> ?nthreads:int
   -> (float, float32_elt) t
   -> (Complex.t, complex32_elt) t
@@ -30,7 +31,7 @@ val rfft
 val irfft
   :  ?axis:int
   -> ?n:int
-  -> ?norm:int
+  -> ?norm:tnorm
   -> ?nthreads:int
   -> (Complex.t, complex32_elt) t
   -> (float, float32_elt) t
@@ -41,8 +42,8 @@ val ifft2 : (Complex.t, complex32_elt) t -> (Complex.t, complex32_elt) t
 
 val dct
   :  ?axis:int
-  -> ?ttype:int
-  -> ?norm:int
+  -> ?ttype:ttrig_transform
+  -> ?norm:tnorm
   -> ?ortho:bool
   -> ?nthreads:int
   -> (float, float32_elt) t
@@ -50,8 +51,8 @@ val dct
 
 val idct
   :  ?axis:int
-  -> ?ttype:int
-  -> ?norm:int
+  -> ?ttype:ttrig_transform
+  -> ?norm:tnorm
   -> ?ortho:bool
   -> ?nthreads:int
   -> (float, float32_elt) t
@@ -59,8 +60,8 @@ val idct
 
 val dst
   :  ?axis:int
-  -> ?ttype:int
-  -> ?norm:int
+  -> ?ttype:ttrig_transform
+  -> ?norm:tnorm
   -> ?ortho:bool
   -> ?nthreads:int
   -> (float, float32_elt) t
@@ -68,8 +69,8 @@ val dst
 
 val idst
   :  ?axis:int
-  -> ?ttype:int
-  -> ?norm:int
+  -> ?ttype:ttrig_transform
+  -> ?norm:tnorm
   -> ?ortho:bool
   -> ?nthreads:int
   -> (float, float32_elt) t