diff --git a/audio.go b/audio.go
index f26076c..1a61c53 100644
--- a/audio.go
+++ b/audio.go
@@ -1,10 +1,18 @@
 package sointu
 
+// AudioSink represents something where we can send audio e.g. audio output.
+// WriteAudio should block if not ready to accept audio e.g. buffer full.
 type AudioSink interface {
 	WriteAudio(buffer []float32) error
 	Close() error
 }
 
+// AudioContext represents the low-level audio drivers. There should be at most
+// one AudioContext at a time. The interface is implemented at least by
+// oto.OtoContext, but in future we could also mock it.
+//
+// AudioContext is used to create one or more AudioSinks with Output(); each can
+// be used to output separate sound & closed when done.
 type AudioContext interface {
 	Output() AudioSink
 	Close() error
diff --git a/audioexport.go b/audioexport.go
index fa6cedb..d5166dc 100644
--- a/audioexport.go
+++ b/audioexport.go
@@ -7,6 +7,11 @@ import (
 	"math"
 )
 
+// Wav converts a stereo signal of 32-bit floats (L R L R..., length should be
+// divisible by 2) into a valid WAV-file, returned as a []byte array.
+//
+// If pcm16 is set to true, the samples in the WAV-file will be 16-bit signed
+// integers; otherwise the samples will be 32-bit floats
 func Wav(buffer []float32, pcm16 bool) ([]byte, error) {
 	buf := new(bytes.Buffer)
 	wavHeader(len(buffer), pcm16, buf)
@@ -17,6 +22,11 @@ func Wav(buffer []float32, pcm16 bool) ([]byte, error) {
 	return buf.Bytes(), nil
 }
 
+// Raw converts a stereo signal of 32-bit floats (L R L R..., length should be
+// divisible by 2) into a raw audio file, returned as a []byte array.
+//
+// If pcm16 is set to true, the samples will be 16-bit signed integers;
+// otherwise the samples will be 32-bit floats
 func Raw(buffer []float32, pcm16 bool) ([]byte, error) {
 	buf := new(bytes.Buffer)
 	err := rawToBuffer(buffer, pcm16, buf)
diff --git a/instrument.go b/instrument.go
index 2e867ed..2393bb6 100644
--- a/instrument.go
+++ b/instrument.go
@@ -8,6 +8,7 @@ type Instrument struct {
 	Units     []Unit
 }
 
+// Copy makes a deep copy of an Instrument
 func (instr *Instrument) Copy() Instrument {
 	units := make([]Unit, len(instr.Units))
 	for i, u := range instr.Units {
diff --git a/order.go b/order.go
index 8abaab2..214a5a8 100644
--- a/order.go
+++ b/order.go
@@ -6,6 +6,7 @@ package sointu
 // necessary amount when a new item is added, filling the unused slots with -1s.
 type Order []int
 
+// Get returns the value at index; or -1 is the index is out of range
 func (s Order) Get(index int) int {
 	if index < 0 || index >= len(s) {
 		return -1
@@ -13,6 +14,7 @@ func (s Order) Get(index int) int {
 	return s[index]
 }
 
+// Set sets the value at index; appending -1s until the slice is long enough.
 func (s *Order) Set(index, value int) {
 	for len(*s) <= index {
 		*s = append(*s, -1)
diff --git a/patch.go b/patch.go
index 5fd14ff..04c9b53 100644
--- a/patch.go
+++ b/patch.go
@@ -9,6 +9,7 @@ import (
 // Patch is simply a list of instruments used in a song
 type Patch []Instrument
 
+// Copy makes a deep copy of a Patch.
 func (p Patch) Copy() Patch {
 	instruments := make([]Instrument, len(p))
 	for i, instr := range p {
@@ -17,6 +18,8 @@ func (p Patch) Copy() Patch {
 	return instruments
 }
 
+// NumVoices returns the total number of voices used in the patch; summing the
+// voices of every instrument
 func (p Patch) NumVoices() int {
 	ret := 0
 	for _, i := range p {
@@ -25,6 +28,8 @@ func (p Patch) NumVoices() int {
 	return ret
 }
 
+// NumDelayLines return the total number of delay lines used in the patch;
+// summing the number of delay lines of every delay unit in every instrument
 func (p Patch) NumDelayLines() int {
 	total := 0
 	for _, instr := range p {
@@ -37,6 +42,8 @@ func (p Patch) NumDelayLines() int {
 	return total
 }
 
+// NumSyns return the total number of sync outputs used in the patch; summing
+// the number of sync outputs of every sync unit in every instrument
 func (p Patch) NumSyncs() int {
 	total := 0
 	for _, instr := range p {
@@ -49,6 +56,11 @@ func (p Patch) NumSyncs() int {
 	return total
 }
 
+// FirstVoiceForInstrument returns the index of the first voice of given
+// instrument. For example, if the Patch has three instruments (0, 1 and 2),
+// with 1, 3, 2 voices, respectively, then FirstVoiceForInstrument(0) returns 0,
+// FirstVoiceForInstrument(1) returns 1 and FirstVoiceForInstrument(2) returns
+// 4. Essentially computes just the cumulative sum.
 func (p Patch) FirstVoiceForInstrument(instrIndex int) int {
 	ret := 0
 	for _, t := range p[:instrIndex] {
@@ -57,6 +69,10 @@ func (p Patch) FirstVoiceForInstrument(instrIndex int) int {
 	return ret
 }
 
+// InstrumentForVoice returns the instrument number for the given voice index.
+// For example, if the Patch has three instruments (0, 1 and 2), with 1, 3, 2
+// voices, respectively, then InstrumentForVoice(0) returns 0,
+// InstrumentForVoice(1) returns 1 and InstrumentForVoice(3) returns 1.
 func (p Patch) InstrumentForVoice(voice int) (int, error) {
 	if voice < 0 {
 		return 0, errors.New("voice cannot be negative")
@@ -70,6 +86,11 @@ func (p Patch) InstrumentForVoice(voice int) (int, error) {
 	return 0, errors.New("voice number is beyond the total voices of an instrument")
 }
 
+// FindSendTarget searches the instrument number and unit index for a unit with
+// the given id. Two units should never have the same id, but if they do, then
+// the first match is returned. Id 0 is interpreted as "no id", thus searching
+// for id 0 returns an error. Error is also returned if the searched id is not
+// found.
 func (p Patch) FindSendTarget(id int) (int, int, error) {
 	if id == 0 {
 		return 0, 0, errors.New("send targets unit id 0")
@@ -84,6 +105,8 @@ func (p Patch) FindSendTarget(id int) (int, int, error) {
 	return 0, 0, fmt.Errorf("send targets an unit with id %v, could not find a unit with such an ID in the patch", id)
 }
 
+// ParamHintString returns a human readable string representing the current
+// value of a given unit parameter.
 func (p Patch) ParamHintString(instrIndex, unitIndex int, param string) string {
 	if instrIndex < 0 || instrIndex >= len(p) {
 		return ""
diff --git a/pattern.go b/pattern.go
index 80cdc8f..389bc55 100644
--- a/pattern.go
+++ b/pattern.go
@@ -6,6 +6,7 @@ package sointu
 // necessary amount when a new item is added, filling the unused slots with 1s.
 type Pattern []byte
 
+// Get returns the value at index; or 1 is the index is out of range
 func (s Pattern) Get(index int) byte {
 	if index < 0 || index >= len(s) {
 		return 1
@@ -13,6 +14,7 @@ func (s Pattern) Get(index int) byte {
 	return s[index]
 }
 
+// Set sets the value at index; appending 1s until the slice is long enough.
 func (s *Pattern) Set(index int, value byte) {
 	for len(*s) <= index {
 		*s = append(*s, 1)
diff --git a/score.go b/score.go
index d7ec303..245a794 100644
--- a/score.go
+++ b/score.go
@@ -1,11 +1,16 @@
 package sointu
 
+// Score represents the arrangement of notes in a song; just a list of tracks
+// and RowsPerPattern and Length (in patterns) to know the desired length of a
+// song in rows. If any of the tracks is too short, all the notes outside the
+// range should be just considered as holding the last note.
 type Score struct {
 	Tracks         []Track
-	RowsPerPattern int
+	RowsPerPattern int // number of rows in each pattern
 	Length         int // length of the song, in number of patterns
 }
 
+// Copy makes a deep copy of a Score.
 func (l Score) Copy() Score {
 	tracks := make([]Track, len(l.Tracks))
 	for i, t := range l.Tracks {
@@ -14,6 +19,8 @@ func (l Score) Copy() Score {
 	return Score{Tracks: tracks, RowsPerPattern: l.RowsPerPattern, Length: l.Length}
 }
 
+// NumVoices returns the total number of voices used in the Score; summing the
+// voices of every track
 func (l Score) NumVoices() int {
 	ret := 0
 	for _, t := range l.Tracks {
@@ -22,6 +29,11 @@ func (l Score) NumVoices() int {
 	return ret
 }
 
+// FirstVoiceForTrack returns the index of the first voice of given track. For
+// example, if the Score has three tracks (0, 1 and 2), with 1, 3, 2 voices,
+// respectively, then FirstVoiceForTrack(0) returns 0, FirstVoiceForTrack(1)
+// returns 1 and FirstVoiceForTrack(2) returns 4. Essentially computes just the
+// cumulative sum.
 func (l Score) FirstVoiceForTrack(track int) int {
 	ret := 0
 	for _, t := range l.Tracks[:track] {
@@ -30,6 +42,8 @@ func (l Score) FirstVoiceForTrack(track int) int {
 	return ret
 }
 
+// LengthInRows returns just RowsPerPattern * Length, as the length is the
+// length in the number of patterns.
 func (l Score) LengthInRows() int {
 	return l.RowsPerPattern * l.Length
 }
diff --git a/song.go b/song.go
index 215db61..335c4e7 100644
--- a/song.go
+++ b/song.go
@@ -4,6 +4,12 @@ import (
 	"errors"
 )
 
+// Song includes a Score(the arrangement of notes in the song in one or more
+// tracks) and a Patch (the list of one or more instruments). Additionally, BPM
+// and RowsPerBeat fields set how fast the song should be played. Currently, BPM
+// is an integer as it offers already quite much granularity for controlling the
+// playback speed, but this could be changed to a floating point in future if
+// finer adjustments are necessary.
 type Song struct {
 	BPM         int
 	RowsPerBeat int
@@ -11,16 +17,20 @@ type Song struct {
 	Patch       Patch
 }
 
+// Copy makes a deep copy of a Score.
 func (s *Song) Copy() Song {
 	return Song{BPM: s.BPM, RowsPerBeat: s.RowsPerBeat, Score: s.Score.Copy(), Patch: s.Patch.Copy()}
 }
 
+// Assuming 44100 Hz playback speed, return the number of samples of each row of
+// the song.
 func (s *Song) SamplesPerRow() int {
 	return 44100 * 60 / (s.BPM * s.RowsPerBeat)
 }
 
-// TBD: Where shall we put methods that work on pure domain types and have no dependencies
-// e.g. Validate here
+// Validate checks if the Song looks like a valid song: BPM > 0, one or more
+// tracks, score uses less than or equal number of voices than patch. Not used
+// much so we could probably get rid of this function.
 func (s *Song) Validate() error {
 	if s.BPM < 1 {
 		return errors.New("BPM should be > 0")
diff --git a/synth.go b/synth.go
index 40236cf..8a88ad4 100644
--- a/synth.go
+++ b/synth.go
@@ -6,17 +6,41 @@ import (
 	"math"
 )
 
+// Synth represents a state of a synthesizer, compiled from a Patch.
 type Synth interface {
+	// Render tries to fill a stereo signal buffer with sound from the
+	// synthesizer, until either the buffer is full or a given number of
+	// timesteps is advanced. In the process, it also fills the syncbuffer with
+	// the values output by sync units. Normally, 1 sample = 1 unit of time, but
+	// speed modulations may change this. It returns the number of samples
+	// filled (! in stereo samples, so the buffer will have 2 * sample floats),
+	// the number of sync outputs written, the number of time steps time
+	// advanced, and a possible error.
 	Render(buffer []float32, syncBuffer []float32, maxtime int) (sample int, syncs int, time int, err error)
+
+	// Update recompiles a patch, but should maintain as much as possible of its
+	// state as reasonable. For example, filters should keep their state and
+	// delaylines should keep their content. Every change in the Patch triggers
+	// an Update and if the Patch would be started fresh every time, it would
+	// lead to very choppy audio.
 	Update(patch Patch) error
+
+	// Trigger triggers a note for a given voice. Called between synth.Renders.
 	Trigger(voice int, note byte)
+
+	// Release releases the currently playing note for a given voice. Called
+	// between synth.Renders.
 	Release(voice int)
 }
 
+// SynthService compiles a given Patch into a Synth, throwing errors if the
+// Patch is malformed.
 type SynthService interface {
 	Compile(patch Patch) (Synth, error)
 }
 
+// Render fills an stereo audio buffer using a Synth, disregarding all syncs and
+// time limits.
 func Render(synth Synth, buffer []float32) error {
 	s, _, _, err := synth.Render(buffer, nil, math.MaxInt32)
 	if err != nil {
@@ -28,6 +52,10 @@ func Render(synth Synth, buffer []float32) error {
 	return nil
 }
 
+// Play plays the Song using a given Synth, returning the stereo audio buffer
+// and the sync buffer as a result (and possible errors). This is a bit
+// illogical as the Song contains already the Patch; this could be probably
+// refactored to just accept a SynthService and a Song.
 func Play(synth Synth, song Song) ([]float32, []float32, error) {
 	err := song.Validate()
 	if err != nil {
diff --git a/track.go b/track.go
index b7ff523..aacd009 100644
--- a/track.go
+++ b/track.go
@@ -1,12 +1,31 @@
 package sointu
 
+// Track represents the patterns and orderlist for each track. Note that each
+// track has its own patterns, so one track cannot use another tracks patterns.
+// This makes the data more intuitive to humans, as the reusing of patterns over
+// tracks is a rather rare occurence. However, the compiler will put all the
+// patterns in one global table (identical patterns only appearing once), to
+// optimize the runtime code.
 type Track struct {
+	// NumVoices is the number of voices this track triggers, cycling through
+	// the voices. When this track triggers a new voice, the previous should be
+	// released.
 	NumVoices int
-	Effect    bool      `yaml:",omitempty"`
-	Order     Order     `yaml:",flow"`
-	Patterns  []Pattern `yaml:",flow"`
+
+	// Effect hints the GUI if this is more of an effect track than a note
+	// track: if true, e.g. the GUI can display the values as hexadecimals
+	// instead of note values.
+	Effect bool `yaml:",omitempty"`
+
+	// Order is a list telling which pattern comes in which order in the song in
+	// this track.
+	Order Order `yaml:",flow"`
+
+	// Patterns is a list of Patterns for this track.
+	Patterns []Pattern `yaml:",flow"`
 }
 
+// Copy makes a deep copy of a Track.
 func (t *Track) Copy() Track {
 	order := make([]int, len(t.Order))
 	copy(order, t.Order)
diff --git a/unit.go b/unit.go
index fc3a09f..9255283 100644
--- a/unit.go
+++ b/unit.go
@@ -2,12 +2,34 @@ package sointu
 
 // Unit is e.g. a filter, oscillator, envelope and its parameters
 type Unit struct {
-	Type       string         `yaml:",omitempty"`
-	ID         int            `yaml:",omitempty"`
+	// Type is the type of the unit, e.g. "add","oscillator" or "envelope".
+	// Always in lowercase. "" type should be ignored, no invalid types should
+	// be used.
+	Type string `yaml:",omitempty"`
+
+	// ID should be a unique ID for this unit, used by SEND units to target
+	// specific units. ID = 0 means that no ID has been given to a unit and thus
+	// cannot be targeted by SENDs. When possible, units that are not targeted
+	// by any SENDs should be cleaned from having IDs, e.g. to keep the exported
+	// data clean.
+	ID int `yaml:",omitempty"`
+
+	// Parameters is a map[string]int of parameters of a unit. For example, for
+	// an oscillator, unit.Type == "oscillator" and unit.Parameters["attack"]
+	// could be 64. Most parameters are either limites to 0 and 1 (e.g. stereo
+	// parameters) or between 0 and 128, inclusive.
 	Parameters map[string]int `yaml:",flow"`
-	VarArgs    []int          `yaml:",flow,omitempty"`
+
+	// VarArgs is a list containing the variable number arguments that some
+	// units require, most notably the DELAY units. For example, for a DELAY
+	// unit, VarArgs is the delaytimes, in samples, of the different delaylines
+	// in the unit.
+	VarArgs []int `yaml:",flow,omitempty"`
 }
 
+// When unit.Type = "oscillator", its unit.Parameter["Type"] tells the type of
+// the oscillator. There is five different oscillator types, so these consts
+// just enumerate them.
 const (
 	Sine   = iota
 	Trisaw = iota
@@ -16,6 +38,7 @@ const (
 	Sample = iota
 )
 
+// Copy makes a deep copy of a unit.
 func (u *Unit) Copy() Unit {
 	parameters := make(map[string]int)
 	for k, v := range u.Parameters {
@@ -26,6 +49,12 @@ func (u *Unit) Copy() Unit {
 	return Unit{Type: u.Type, Parameters: parameters, VarArgs: varArgs, ID: u.ID}
 }
 
+// StackChange returns how this unit will affect the signal stack. "pop" and
+// "addp" and such will consume the topmost signal, and thus return -1 (or -2,
+// if the unit is a stereo unit). On the other hand, "oscillator" and "envelope"
+// will produce a signal, and thus return 1 (or 2, if the unit is a stereo
+// unit). Effects that just change the topmost signal and will not change the
+// number of signals on the stack and thus return 0.
 func (u *Unit) StackChange() int {
 	switch u.Type {
 	case "addp", "mulp", "pop", "out", "outaux", "aux":
@@ -42,6 +71,9 @@ func (u *Unit) StackChange() int {
 	return 0
 }
 
+// StackNeed returns the number of signals that should be on the stack before
+// this unit is executed. Used to prevent stack underflow. Units producing
+// signals do not care what is on the stack before and will return 0.
 func (u *Unit) StackNeed() int {
 	switch u.Type {
 	case "", "envelope", "oscillator", "noise", "receive", "loadnote", "loadval", "in":
diff --git a/unittype.go b/unittype.go
index 424f11a..08a8361 100644
--- a/unittype.go
+++ b/unittype.go
@@ -134,6 +134,10 @@ var UnitTypes = map[string]([]UnitParameter){
 	"sync": []UnitParameter{},
 }
 
+// Ports is static map allowing quickly finding the parameters of a unit that
+// can be modulated. This is populated based on the UnitTypes list during
+// init(). Thus, should be immutable, but Go not supporting that, then this will
+// have to suffice: DO NOT EVER CHANGE THIS MAP.
 var Ports = make(map[string]([]string))
 
 func init() {