diff --git a/compiler/encoded_song.go b/compiler/encoded_song.go
index 703da45..2cdd2e3 100644
--- a/compiler/encoded_song.go
+++ b/compiler/encoded_song.go
@@ -15,112 +15,163 @@ type EncodedSong struct {
 	Sequences [][]byte
 }
 
-// flattenPatterns returns the track sequences flattened into linear arrays.
-// Additionally, after first release (value 0), it replaces every release or
-// hold with -1, denoting "don't care if it's either release (0) or hold (1)".
-// As we reconstruct the pattern table, we may use any pattern that has either 0
-// or hold in place of don't cares.
-func flattenPatterns(song *sointu.Song) [][]int {
-	ret := make([][]int, 0, len(song.Tracks))
-	for _, t := range song.Tracks {
-		flatSequence := make([]int, 0, song.TotalRows())
-		dontCare := false
-		for _, s := range t.Sequence {
-			for _, note := range t.Patterns[s] {
-				if !dontCare || note > song.Hold {
-					if note == song.Hold {
-						flatSequence = append(flatSequence, 1) // replace holds with 1s, we'll get rid of song.Hold soon and do the hold replacement at the last minute
-					} else {
-						flatSequence = append(flatSequence, int(note))
-					}
-					dontCare = note == 0 // after 0 aka release, we don't care if further releases come along
-				} else {
-					flatSequence = append(flatSequence, -1)
-				}
-			}
+// fixPatternLength makes sure that every pattern is the same length. During
+// composing. Patterns shorter than the given length are padded with 1 / "hold";
+// patterns longer than the given length are cropped.
+func fixPatternLength(patterns [][]byte, fixedLength int) [][]int {
+	patternData := make([]int, len(patterns)*fixedLength)
+	ret := make([][]int, len(patterns))
+	for i, pat := range patterns {
+		for j, note := range pat {
+			patternData[j] = int(note)
 		}
-		ret = append(ret, flatSequence)
+		for j := len(pat); j < fixedLength; j++ {
+			patternData[j] = 1 // pad with hold
+		}
+		ret[i], patternData = patternData[:fixedLength], patternData[fixedLength:]
 	}
 	return ret
 }
 
-// constructPatterns finds the smallest global pattern table for a given list of
-// flattened patterns. If the patterns are not divisible with the patternLength,
-// then: a) if the last note of a track is release (0) or don't care (-1), the
-// track is extended with don't cares (-1) until the total length of the song is
-// divisible with the patternLength. b) Otherwise, the track is extended with a
-// single release (0), followed by don't care about release & hold (-1).
-//
-// In otherwords: any playing notes are released when the original song ends.
-func constructPatterns(tracks [][]int, patternLength int) ([][]byte, [][]byte, error) {
-	patternTable := make([][]int, 0)
-	sequences := make([][]byte, 0, len(tracks))
-	for _, t := range tracks {
-		var sequence []byte
-		for s := 0; s < len(t); s += patternLength {
-			pat := t[s : s+patternLength]
-			if len(pat) < patternLength {
-				extension := make([]int, patternLength-len(pat))
-				for i := range extension {
-					if pat[len(pat)-1] > 0 && i == 0 {
-						extension[i] = 0
-					} else {
-						extension[i] = -1
-					}
-				}
-				pat = append(pat, extension...)
+// flattenSequence looks up a sequence of patterns and concatenates them into a
+// single linear array of notes. Note that variable length patterns are
+// concatenated as such; call fixPatternLength first if you want every pattern
+// to be constant length.
+func flattenSequence(patterns [][]int, sequence []int) []int {
+	sumLen := 0
+	for _, patIndex := range sequence {
+		sumLen += len(patterns[patIndex])
+	}
+	notes := make([]int, sumLen)
+	window := notes
+	for _, patIndex := range sequence {
+		elementsCopied := copy(window, patterns[patIndex])
+		window = window[elementsCopied:]
+	}
+	return notes
+}
+
+// markDontCares goes through a linear array of notes and marks every hold (1)
+// or release (0) after the first release (0) as -1 or "don't care". This means
+// that for -1:s, we don't care if it's a hold or release; it does not affect
+// the sound as the note has been already released.
+func markDontCares(notes []int) []int {
+	notesWithDontCares := make([]int, len(notes))
+	dontCare := false
+	for i, n := range notes {
+		if dontCare && n <= 1 {
+			notesWithDontCares[i] = -1
+		} else {
+			notesWithDontCares[i] = n
+			dontCare = n == 0
+		}
+	}
+	return notesWithDontCares
+}
+
+// replaceInt replaces all occurrences of needle in the haystack with the value
+// "with"
+func replaceInts(haystack []int, needle int, with int) {
+	for i, v := range haystack {
+		if v == needle {
+			haystack[i] = with
+		}
+	}
+}
+
+// splitSequence splits a linear sequence of notes into patternLength size
+// chunks. If the last chunk is shorter than the patternLength, then it is
+// padded with dontCares (-1).
+func splitSequence(sequence []int, patternLength int) [][]int {
+	numChunksRoundedUp := (len(sequence) + patternLength - 1) / patternLength
+	chunks := make([][]int, numChunksRoundedUp)
+	for i := range chunks {
+		if len(sequence) >= patternLength {
+			chunks[i], sequence = sequence[:patternLength], sequence[patternLength:]
+		} else {
+			padded := make([]int, patternLength)
+			j := copy(padded, sequence)
+			for ; j < patternLength; j++ {
+				padded[j] = -1
 			}
-			// go through the current pattern table to see if there's already a
-			// pattern that could be used
-			patternIndex := -1
-			for j, p := range patternTable {
-				match := true
-				for k, n := range p {
-					if (n > -1 && pat[k] > -1 && n != pat[k]) ||
-						(n == -1 && pat[k] > 1) ||
-						(n > 1 && pat[k] == -1) {
-						match = false
-						break
-					}
-				}
-				if match {
-					// if there was any don't cares in the pattern table where
-					// the new pattern has non don't cares, copy them to the
-					// patterns that was already in the pattern table
-					for k, n := range pat {
-						if n != -1 {
-							patternTable[j][k] = n
-						}
-					}
-					patternIndex = j
+			chunks[i] = padded
+		}
+	}
+	return chunks
+}
+
+// addPatternsToTable adds given patterns to the table, checking if existing
+// pattern could be used. DontCares are taken into account so a pattern that has
+// don't care where another has a hold or release is ok. It returns a 1D
+// sequence of indices of each added pattern in the updated pattern table & the
+// updated pattern table.
+func addPatternsToTable(patterns [][]int, table [][]int) ([]int, [][]int) {
+	updatedTable := make([][]int, len(table))
+	copy(updatedTable, table) // avoid updating the underlying slices for concurrency safety
+	sequence := make([]int, len(patterns))
+	for i, pat := range patterns {
+		// go through the current pattern table to see if there's already a
+		// pattern that could be used
+		patternIndex := -1
+		for j, p := range updatedTable {
+			match := true
+			identical := true
+			for k, n := range p {
+				if (n > -1 && pat[k] > -1 && n != pat[k]) ||
+					(n == -1 && pat[k] > 1) ||
+					(n > 1 && pat[k] == -1) {
+					match = false
 					break
 				}
+				if n != pat[i] {
+					identical = false
+				}
 			}
-			if patternIndex == -1 {
-				patternIndex = len(patternTable)
-				patternTable = append(patternTable, pat)
-			}
-			if patternIndex > 255 {
-				return nil, nil, errors.New("encoding the song would result more than 256 different unique patterns")
-			}
-			sequence = append(sequence, byte(patternIndex))
-		}
-		sequences = append(sequences, sequence)
-	}
-	// finally, if there are still some don't cares in the table, just replace them with zeros
-	byteTable := make([][]byte, 0, len(patternTable))
-	for _, pat := range patternTable {
-		bytePat := make([]byte, 0, patternLength)
-		for _, n := range pat {
-			if n >= 0 {
-				bytePat = append(bytePat, byte(n))
-			} else {
-				bytePat = append(bytePat, 0)
+			if match {
+				if !identical {
+					// the patterns were not identical; one of them had don't
+					// cares where another had hold or release so we make a new
+					// copy with merged data, that essentially is a max of the
+					// two patterns
+					mergedPat := make([]int, len(p))
+					copy(mergedPat, p) // make a copy instead of updating existing, for concurrency safety
+					for k, n := range pat {
+						if n != -1 {
+							mergedPat[k] = n
+						}
+					}
+					updatedTable[j] = mergedPat
+				}
+				patternIndex = j
+				break
 			}
 		}
-		byteTable = append(byteTable, bytePat)
+		if patternIndex == -1 {
+			patternIndex = len(updatedTable)
+			updatedTable = append(updatedTable, pat)
+		}
+		sequence[i] = patternIndex
 	}
-	return byteTable, sequences, nil
+	return sequence, updatedTable
+}
+
+func intsToBytes(array []int) ([]byte, error) {
+	ret := make([]byte, len(array))
+	for i, v := range array {
+		if v < 0 || v > 255 {
+			return nil, fmt.Errorf("when converting intsToBytes, all values should be 0 .. 255 (was: %v)", v)
+		}
+		ret[i] = byte(v)
+	}
+	return ret, nil
+}
+
+func bytesToInts(array []byte) []int {
+	ret := make([]int, len(array))
+	for i, v := range array {
+		ret[i] = int(v)
+	}
+	return ret
 }
 
 func (e *EncodedSong) PatternLength() int {
@@ -136,11 +187,31 @@ func (e *EncodedSong) TotalRows() int {
 }
 
 func EncodeSong(song *sointu.Song) (*EncodedSong, error) {
-	// TODO: we could give the user the possibility to encode the patterns with a different length here also
 	patLength := song.PatternRows()
-	patterns, sequences, err := constructPatterns(flattenPatterns(song), patLength)
-	if err != nil {
-		return nil, fmt.Errorf("error during constructPatterns: %v", err)
+	sequences := make([][]byte, len(song.Tracks))
+	var patterns [][]int
+	for i, t := range song.Tracks {
+		fixed := fixPatternLength(t.Patterns, patLength)
+		flat := flattenSequence(fixed, bytesToInts(t.Sequence))
+		dontCares := markDontCares(flat)
+		// TODO: we could give the user the possibility to use another length during encoding that during composing
+		chunks := splitSequence(dontCares, patLength)
+		var sequence []int
+		sequence, patterns = addPatternsToTable(chunks, patterns)
+		var err error
+		sequences[i], err = intsToBytes(sequence)
+		if err != nil {
+			return nil, errors.New("the constructed pattern table would result in > 256 unique patterns; only 256 unique patterns are supported")
+		}
 	}
-	return &EncodedSong{Patterns: patterns, Sequences: sequences}, nil
+	bytePatterns := make([][]byte, len(patterns))
+	for i, pat := range patterns {
+		var err error
+		replaceInts(pat, -1, 0) // replace don't cares with releases
+		bytePatterns[i], err = intsToBytes(pat)
+		if err != nil {
+			return nil, fmt.Errorf("invalid note in pattern, notes should be 0 .. 255: %v", err)
+		}
+	}
+	return &EncodedSong{Patterns: bytePatterns, Sequences: sequences}, nil
 }