mix.v0: gopkg.in/mix.v0 Index | Files | Directories

package mix

import "gopkg.in/mix.v0"

Sequence-based Go-native audio mixer for music apps

Go-native audio mixer for Music apps

See `demo/demo.go`:

package main

import (


var (
  sampleHz   = float64(48000)
  spec = bind.AudioSpec{
    Freq:     sampleHz,
    Format:   bind.AudioF32,
    Channels: 2,
  bpm        = 120
  step       = time.Minute / time.Duration(bpm*4)
  loops      = 16
  prefix     = "sound/808/"
  kick1      = "kick1.wav"
  kick2      = "kick2.wav"
  marac      = "maracas.wav"
  snare      = "snare.wav"
  hitom      = "hightom.wav"
  clhat      = "cl_hihat.wav"
  pattern    = []string{

func main() {
  defer mix.Teardown()

  mix.StartAt(time.Now().Add(1 * time.Second))

  t := 2 * time.Second // padding before music
  for n := 0; n < loops; n++ {
    for s := 0; s < len(pattern); s++ {
      mix.SetFire(pattern[s], t+time.Duration(s)*step, 0, 1.0, 0)
    t += time.Duration(len(pattern)) * step

  fmt.Printf("Mix, pid:%v, spec:%v\n", os.Getpid(), spec)
  for mix.FireCount() > 0 {
    time.Sleep(1 * time.Second)

Play this Demo from the root of the project, using SDL 2.0 for hardware audio playback:

make demo

Or export WAV via stdout `> demo/output.wav`:

make demo.wav


Game audio mixers are designed to play audio spontaneously, but when the timing is known in advance (e.g. sequence-based music apps) there is a demand for much greater accuracy in playback timing.

Read the API documentation at https://godoc.org/gopkg.in/mix.v0

Mix seeks to solve the problem of audio mixing for the purpose of the playback of sequences where audio files and their playback timing is known in advance.

Mix stores and mixes audio in native Go `[]float64` and natively implements Paul Vögler's "Loudness Normalization by Logarithmic Dynamic Range Compression" (details below)

Author: Charney Kaye <hiya@charney.io>


Even after selecting a hardware interface library such as http://www.portaudio.com/ or https://www.libsdl.org/, there remains a critical design problem to be solved.

This design is a music application mixer. Most available options are geared towards Game development.

Game audio mixers offer playback timing accuracy +/- 2 milliseconds. But that's totally unacceptable for music, specifically sequence-based sample playback.

The design pattern particular to Game design is that the timing of the audio is not know in advance- the timing that really matters is that which is assembled in near-real-time in response to user interaction.

In the field of Music development, often the timing is known in advance, e.g. a sequencer, the composition of music by specifying exactly how, when and which audio files will be played relative to the beginning of playback.

Ergo, mix seeks to solve the problem of audio mixing for the purpose of the playback of sequences where audio files and their playback timing is known in advance. It seeks to do this with the absolute minimal logical overhead on top of the audio interface.

Mix takes maximum advantage of Go by storing and mixing audio in native Go `[]float64` and natively implementing Paul Vögler's "Loudness Normalization by Logarithmic Dynamic Range Compression" (see The Mixing Algorithm below)


To the Mix API, time is specified as a time.Duration-since-epoch, where the epoch is the moment that mix.Start() was called.

Internally, time is tracked as samples-since-epoch at the master out playback frequency (e.g. 48000 Hz). This is most efficient because source audio is pre-converted to the master out playback frequency, and all audio maths are performed in terms of samples.

The Mixing Algorithm

Inspired by the theory paper "Mixing two digital audio streams with on the fly Loudness Normalization by Logarithmic Dynamic Range Compression" by Paul Vögler, 2012-04-20. This paper is published at http://www.voegler.eu/pub/audio/digital-audio-mixing-and-normalization.html.


There's a demo implementation of mix included in the `demo/` folder in this repository. Run it using the defaults:

go run 808.go

Or specify options, e.g. using SDL for playback

go run 808.go --playback sdl

To show the help screen:

go run 808.go --help




sudo apt-get install libsdl2-dev

Mac OS X:

brew install sdl2

More details for Linux, Mac and Windows: http://lazyfoo.net/SDL_tutorials/lesson01/index.php



sudo apt-get install portaudio19-dev

Mac OS X:

brew install portaudio

Windows: https://gnuradio.org/redmine/projects/gnuradio/wiki/PortAudioInstall.

This project is in Alpha and the API is subject to change

Best efforts will be made to preserve each API version in a release tag that can be parsed, e.g. http://gopkg.in/mix.v0

Mix in good health!


Package Files


func ClearAllFires Uses

func ClearAllFires()

ClearAllFires to clear all fires currently ready, or live

func Configure Uses

func Configure(s spec.AudioSpec)

Configure the mixer frequency, format, channels & sample rate.

func Debug Uses

func Debug(isOn bool)

Debug ON/OFF (ripples down to all sub-modules)

func FireCount Uses

func FireCount() int

FireCount to check the number of fires currently scheduled for playback

func GetNowAt Uses

func GetNowAt() time.Duration

GetNowAt returns current mix position

func GetStartTime Uses

func GetStartTime() time.Time

GetStartTime the mixer was started at

func OutputClose Uses

func OutputClose()

OutputBegin to output WAV closer as []byte via stdout

func OutputContinueTo Uses

func OutputContinueTo(t time.Duration)

OutputContinueTo output as []byte via stdout, up to a specified duration-since-start

func OutputStart Uses

func OutputStart(length time.Duration)

OutputStart requires a known length

func SetFire Uses

func SetFire(source string, begin time.Duration, sustain time.Duration, volume float64, pan float64) *fire.Fire

SetFire to represent a single audio source playing at a specific time in the future (in time.Duration from play start), with sustain time.Duration, volume from 0 to 1, and pan from -1 to +1

func SetMixCycleDuration Uses

func SetMixCycleDuration(d time.Duration)

Set the duration between "mix cycles", wherein garbage collection is performed.

func SetSoundsPath Uses

func SetSoundsPath(prefix string)

SetSoundsPath prefix

func Spec Uses

func Spec() *spec.AudioSpec

Spec for the mixer, which may include callback functions, e.g. portaudio

func Start Uses

func Start()

Start the mixer now

func StartAt Uses

func StartAt(t time.Time)

StartAt a specific time in the future

func Teardown Uses

func Teardown()

Teardown everything and release all memory.


bindPackage bind is for modular binding of mix to audio interface
bind/debugPackage debug for debugging
bind/hardware/nullPackage null is for modular binding of mix to a null (mock) audio interface
bind/hardware/portaudioPackage portaudio is for modular binding of mix to audio interface via PortAudio
bind/hardware/sdlPackage sdl is for modular binding of mix to audio interface via SDL2
bind/optPackage opt specifies valid options
bind/samplePackage sample models an audio sample
bind/specPackage spec specifies valid audio formats
bind/wavPackage wav is direct WAV filo I/O
lib/firePackage fire model an audio source playing at a specific time
lib/mixPackage mix combines sources into an output audio stream
lib/sourcePackage source models a single audio source

Package mix imports 6 packages (graph) and is imported by 4 packages. Updated 2018-02-11. Refresh now. Tools for package owners.