diff --git a/Midi files/Bach_Air_on_G_String_BWV1068.mid b/Midi files/Bach_Air_on_G_String_BWV1068.mid
index e81a505..472b565 100644
Binary files a/Midi files/Bach_Air_on_G_String_BWV1068.mid and b/Midi files/Bach_Air_on_G_String_BWV1068.mid differ
diff --git a/Midi files/Bach_invention_10_Gmajor.mid b/Midi files/Bach_invention_10_Gmajor.mid
index 7e73dad..c12e781 100644
Binary files a/Midi files/Bach_invention_10_Gmajor.mid and b/Midi files/Bach_invention_10_Gmajor.mid differ
diff --git a/Midi files/Bach_invention_4_Dminor.mid b/Midi files/Bach_invention_4_Dminor.mid
index 1ba42e6..177077f 100644
Binary files a/Midi files/Bach_invention_4_Dminor.mid and b/Midi files/Bach_invention_4_Dminor.mid differ
diff --git a/MusicCore.Tests/ChomskyAnalysisTest.cs b/MusicCore.Tests/ChomskyAnalysisTest.cs
index 925c826..6a1a1a1 100644
--- a/MusicCore.Tests/ChomskyAnalysisTest.cs
+++ b/MusicCore.Tests/ChomskyAnalysisTest.cs
@@ -12,7 +12,7 @@ public class ChomskyAnalysisTest
         [DataTestMethod]
         public void Albinoni_Adagio(string filename)
         {
-            Test(filename);
+            Test(filename, int.MaxValue, new Fraction(1,8));
         }
 
         [DataRow(@"Bach_invention_1_Cmajor.mid")]
@@ -24,14 +24,14 @@ public void Albinoni_Adagio(string filename)
         [DataTestMethod]
         public void Bach_inventions(string filename)
         {
-            Test(filename);
+            Test(filename, int.MaxValue, new Fraction(1, 96));
         }
 
         [DataRow(@"Bach_Air_on_G_String_BWV1068.mid")]
-        [DataTestMethod, Ignore]
+        [DataTestMethod]
         public void Bach_Air_on_G_String(string filename)
         {
-            Test(filename);
+            Test(filename, int.MaxValue, new Fraction(1, 24));
         }
 
         [DataRow(@"Mozart_Symphony40_Allegro.mid")]
@@ -41,9 +41,9 @@ public void Mozart_Symphony40_Allegro(string filename)
             Test(filename, 2);
         }
 
-        private void Test(string filename, int take = int.MaxValue)
+        private void Test(string filename, int take = int.MaxValue, Fraction? prec = null)
         {
-            var lists = MidiFileReader.Read(filename).GetVoices().Take(take).ToList();
+            var lists = MidiFileReader.Read(filename, prec).GetVoices().Take(take).ToList();
 
             // Save copy
             var copy = FlatCopy(lists);
diff --git a/MusicCore/Fraction.cs b/MusicCore/Fraction.cs
index b1fa841..3a1a72d 100644
--- a/MusicCore/Fraction.cs
+++ b/MusicCore/Fraction.cs
@@ -65,6 +65,11 @@ public static Fraction Min(Fraction a, Fraction b)
             return new Fraction(f.p * n, f.q);
         }
 
+        public static Fraction operator/(Fraction f1, Fraction f2)
+        {
+            return new Fraction(f1.p * f2.q, f1.q * f2.p);
+        }
+
         #region Equals and GetHashCode
         public override bool Equals(object obj)
         {
@@ -97,6 +102,11 @@ static public implicit operator Fraction(int n)
             return new Fraction(n, 1);
         }
 
+        public bool IsWhole()
+        {
+            return p % q == 0;
+        }
+
         public override string ToString()
         {
             if (q == 1)
diff --git a/MusicCore/MidiFileReader.cs b/MusicCore/MidiFileReader.cs
index 3b63937..3c98572 100644
--- a/MusicCore/MidiFileReader.cs
+++ b/MusicCore/MidiFileReader.cs
@@ -1,14 +1,27 @@
-using System.Collections.Generic;
-using NAudio.Midi;
+using NAudio.Midi;
+using System;
 
 namespace MusicCore
 {
     public static class MidiFileReader
     {
-        public static Composition Read(string filename)
+        private static void AddNote(MelodyPartList list, NoteWithDuration nwd, Fraction? prec = null, long absoluteTime = 0)
+        {
+            if (prec != null)
+            {
+                Fraction times = (nwd.Duration / prec.Value);
+                if (!times.IsWhole())
+                    throw new Exception($"Duration of Note {nwd} not divisible by {prec.Value} at absoluteTime={absoluteTime}");
+            }
+
+            list.Add(nwd);
+        }
+
+        public static Composition Read(string filename, Fraction? prec = null)
         {
             MidiFile midi = new MidiFile(filename, true);
             Composition composition = new Composition();
+            int quarterNoteInTicks = midi.DeltaTicksPerQuarterNote;
 
             for (int track = 0; track < midi.Tracks; track++)
             {
@@ -20,14 +33,16 @@ public static Composition Read(string filename)
                         if (noteonevent.OffEvent != null)
                         {
                             if (noteonevent.DeltaTime > 0)
-                                list.Add(new NoteWithDuration(new Fraction(noteonevent.DeltaTime, 120)));
+                                AddNote(list, new NoteWithDuration(new Fraction(noteonevent.DeltaTime, quarterNoteInTicks)), prec, noteonevent.AbsoluteTime);
 
-                            list.Add(
+                            AddNote(
+                                list,
                                 new NoteWithDuration(
                                     noteonevent.NoteNumber,
                                     Alteration.Natural,
-                                    new Fraction(noteonevent.NoteLength, 120)));
-
+                                    new Fraction(noteonevent.NoteLength, quarterNoteInTicks)),
+                                prec,
+                                noteonevent.AbsoluteTime);
                         }
                     }
                     else