clamped box-muller values between [-3,3] and re-scale to achieve a no…

…rmal [0,1] value range

src/Sound/Tidal/UI.hs

@@ -232,14 +232,16 @@ d1 $
 Implemented with the Box-Muller transform.
   * the max ensures we don't calculate log 0
   * the rot in u2 ensures we don't just get the same value as u1
+  * clamp the Box-Muller generated values in a [-3,3] range
 -}
 normal :: (Floating a, Ord a) => Pattern a
 normal = do
-  u1 <- max 0.0000001 <$> rand
-  u2 <- rot 1 rand
-  let r1 = sqrt (-2 * log u1)
+  u1 <- max 0.001 <$> rand
+  u2 <- rotL 1 rand
+  let r1 = sqrt $ - (2 * log u1)
       r2 = cos (2 * pi * u2)
-  pure ((r1 * r2) + 1) / 2
+      clamp n = max (-3) (min 3 n)
+  pure $ clamp (r1 * r2 + 3) / 6
 
 {- | Randomly picks an element from the given list.
 

test/Sound/Tidal/UITest.hs

@@ -142,14 +142,14 @@ run =
     describe "normal" $ do
       it "produces values within [0,1] in a bell curve" $ do
         it "at the start of a cycle" $
-          queryArc normal (Arc 0 0) `shouldBe` 
-            [Event (Context []) Nothing (Arc 0 0) (0.3370977:: Float)]
+          queryArc normal (Arc 0 0.1) `shouldBe` 
+            [Event (Context []) Nothing (Arc 0 0.1) (0.5 :: Double)]
         it "at 1/4 of a cycle" $
           queryArc normal (Arc 0.25 0.25) `shouldBe`
-            [Event (Context []) Nothing (Arc 0.25 0.25) (0.4723987:: Float)]
+            [Event (Context []) Nothing (Arc 0.25 0.25) (0.47110511611574907 :: Double)]
         it "at 3/4 of a cycle" $
           queryArc normal (Arc 0.75 0.75) `shouldBe`
-          [Event (Context []) Nothing (Arc 0.75 0.75) (0.44856572:: Float)]
+          [Event (Context []) Nothing (Arc 0.75 0.75) (0.5 :: Double)]
 
     describe "range" $ do
       describe "scales a pattern to the supplied range" $ do