Documentation ¶
Overview ¶
Sequence-based Go-native audio mixer for music apps
Go-native audio mixer for Music apps ¶
See `demo/demo.go`:
package main import ( "fmt" "os" "time" "gopkg.in/mix.v0" "gopkg.in/mix.v0/bind" ) 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{ kick2, marac, clhat, marac, snare, marac, clhat, kick2, marac, marac, hitom, marac, snare, kick1, clhat, marac, } ) func main() { defer mix.Teardown() mix.Debug(true) mix.Configure(spec) mix.SetSoundsPath(prefix) 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
What ¶
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>
Why ¶
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)
Time ¶
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.
Usage ¶
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
Dependencies ¶
SDL2 ¶
Ubuntu:
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
Portaudio ¶
Ubuntu:
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!
Index ¶
- func ClearAllFires()
- func Configure(s spec.AudioSpec)
- func Debug(isOn bool)
- func FireCount() int
- func GetNowAt() time.Duration
- func GetStartTime() time.Time
- func OutputClose()
- func OutputContinueTo(t time.Duration)
- func OutputStart(length time.Duration)
- func SetFire(source string, begin time.Duration, sustain time.Duration, volume float64, ...) *fire.Fire
- func SetMixCycleDuration(d time.Duration)
- func SetSoundsPath(prefix string)
- func Spec() *spec.AudioSpec
- func Start()
- func StartAt(t time.Time)
- func Teardown()
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func ClearAllFires ¶ added in v0.0.3
func ClearAllFires()
ClearAllFires to clear all fires currently ready, or live
func FireCount ¶ added in v0.0.3
func FireCount() int
FireCount to check the number of fires currently scheduled for playback
func GetStartTime ¶ added in v0.0.2
GetStartTime the mixer was started at
func OutputClose ¶ added in v0.0.4
func OutputClose()
OutputBegin to output WAV closer as []byte via stdout
func OutputContinueTo ¶ added in v0.0.4
OutputContinueTo output as []byte via stdout, up to a specified duration-since-start
func OutputStart ¶ added in v0.0.4
OutputStart requires a known length
func SetFire ¶
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 ¶ added in v0.0.3
Set the duration between "mix cycles", wherein garbage collection is performed.
Types ¶
This section is empty.
Directories ¶
Path | Synopsis |
---|---|
Package bind is for modular binding of mix to audio interface
|
Package bind is for modular binding of mix to audio interface |
debug
Package debug for debugging
|
Package debug for debugging |
hardware/null
Package null is for modular binding of mix to a null (mock) audio interface
|
Package null is for modular binding of mix to a null (mock) audio interface |
hardware/portaudio
Package portaudio is for modular binding of mix to audio interface via PortAudio
|
Package portaudio is for modular binding of mix to audio interface via PortAudio |
hardware/sdl
Package sdl is for modular binding of mix to audio interface via SDL2
|
Package sdl is for modular binding of mix to audio interface via SDL2 |
opt
Package opt specifies valid options
|
Package opt specifies valid options |
sample
Package sample models an audio sample Package sample models an audio sample
|
Package sample models an audio sample Package sample models an audio sample |
spec
Package spec specifies valid audio formats
|
Package spec specifies valid audio formats |
wav
Package wav is direct WAV filo I/O Package wav is direct WAV filo I/O Package wav is direct WAV filo I/O Package wav is direct WAV filo I/O
|
Package wav is direct WAV filo I/O Package wav is direct WAV filo I/O Package wav is direct WAV filo I/O Package wav is direct WAV filo I/O |
lib
|
|
fire
Package fire model an audio source playing at a specific time
|
Package fire model an audio source playing at a specific time |
mix
Package mix combines sources into an output audio stream
|
Package mix combines sources into an output audio stream |
source
Package source models a single audio source Package source models a single audio source
|
Package source models a single audio source Package source models a single audio source |