building modern audio apps with avaudioengine

@bobmccuneBob McCune

with AVAudioEngineBuilding Modern Audio Apps

-MN Developer and Instructor

-Owner of TapHarmonic, LLC.

-Author of Learning AV Foundation

About...Bob McCune

http://LearningAVFoundation.com

-What is AVAudioEngine? - Goals and Capabilities

-Understanding AVAudioEngine - Understanding Audio Nodes - Playing and Recording Audio - Audio Mixing and Effect Processing - Working with MIDI and Samplers

AgendaWhat will I learn?

AV Foundation EvolutionHumble Beginnings

AV Foundation

MediaPlayer AVKit

UIKit AppKit

Core Video Core MediaCore Animation

Audio-Only

Core Audio

MavericksiOS 7

AV Foundation EvolutionHumble Beginnings

AVKit AVKit

UIKit AppKit

Core Video Core MediaCore Animation Core Audio

AVF Video AVF Audio

YosemiteiOS 8

AVAudioEngineAn Introduction

-Objective-C API simplifying low-latency, real-time audio -Features and Capabilities:

- Read and write audio files in all Core Audio supported formats - Play and record audio using files and buffers - Dynamically configure audio processing blocks - Perform audio tap processing - Perform Stereo and 3D mixing off audio signals - MIDI playback and control over sampler instruments

AVAudioEngineCore Audio for Mortals

Sample Use CasesWhat kind of apps can you build?

-Manages graphs of audio nodes -Connects audio node into active chains -Dynamically attach and reconfigure graph -Start and stop the engine

The EngineAVAudioEngine

-Nodes are audio blocks - Source Nodes: Player, Microphone - Processing Nodes: Mixer, Audio Unit Effect - Destination: Speaker, Headphones

NodesAVAudioNode

-AVAudioEngine provides 3 implicit nodes: - AVAudioInputNode: system input, cannot be created - AVAudioOutputNode: system output, cannot be created - AVAudioMixerNode: mixes multiple inputs to a single output

-Nodes are connected via their input and output busses - Most nodes have one input and one output

- AVAudioMixerNode has multiple inputs and one output - Busses have an associated audio format

NodesAVAudioNode

-Nodes are connected to form an active chain - Source Node Destination Node = Active Chain - Establishes and active render thread

Node ConnectionsEstablishing Active Chains

DestinationNode

(Output)

SourceNode

(Player)

Node ConnectionsEstablishing Active Chains

DestinationNode

(Output)

SourceNode

(Player)

Processing Node

(Mixer)

-Nodes are connected to form an active chain - Source Node Destination Node = Active Chain - Establishes and active render thread

Node ConnectionsEstablishing Active Chains

DestinationNode

(Output)

SourceNode

(Player)

Processing Node

(Mixer)X

-Nodes are connected to form an active chain - Source Node Destination Node = Active Chain - Establishes and active render thread

1. Create the engine 2. Create the nodes 3. Attach the nodes to the engine 4. Connect the nodes together 5. Start the engine

Basic RecipeConfiguring the Graph

Engine SetupBasic Recipe// 1. Create engine (example only, needs to be strong reference) AVAudioEngine *engine = [[AVAudioEngine alloc] init];

// 2. Create a player node AVAudioPlayerNode *player = [[AVAudioPlayerNode alloc] init];

// 3. Attach node to the engine [engine attachNode:player];

// 4. Connect player node to engine's main mixer AVAudioMixerNode *mixer = engine.mainMixerNode; [engine connect:player to:mixer format:[mixer outputFormatForBus:0]];

// 5. Start engine NSError *error; if (![engine startAndReturnError:&error]) { // handle error }

Playing AudioPlayers, Files, and Buffers

Files, Buffers, and Formats

AVAudioPCMBuffer

AVAudioFormat

AVAudioFile

-Reads and writes files in all Core Audio supported formats -Automatically decodes when reading, encodes when writing

- Does not support sample rate conversion

-File has both a file format and a processing format - fileFormat: on-disk format - processingFormat: uncompressed, in-memory format - Both are instances of AVAudioFormat

Audio FilesAVAudioFile

-Provides a format descriptor for the digital audio samples - Provides access to sample rate, channel count, interleaving, etc. - Wrapper over Core Audio AudioStreamBasicDescription

-Core Audio uses a “Standard” format for both platforms - Noninterleaved linear PCM, 32-bit floating point samples - Canonical formats are deprecated!

-Additionally supports “Common” formats - AVAudioCommonFormat: 16/32-bit integer, 32/64-but floating point

Audio FormatsAVAudioFormat

-Memory buffer for audio data in any Linear PCM format - Format and buffer capacity defined upon creation

-Provides a wrapper over a Core Audio AudioBufferList - audioBufferList and mutableAudioBufferList properties

Audio BuffersAVAudioPCMBuffer

@property (nonatomic, readonly) float * const *floatChannelData; @property (nonatomic, readonly) int16_t * const *int16ChannelData; @property (nonatomic, readonly) int32_t * const *int32ChannelData;

-Sample data accessed using:

-Pushes audio data onto the active render thread -Schedule audio data from files and buffers

- Scheduled to play immediately or at future time - Future times specified with AVAudioTime

- Files - Schedule file or file segment with completion callback

- Buffers - Schedule multiple buffers with individual completion callbacks - Schedule looping buffer

Player NodesAVAudioPlayerNode

Creating Files and BuffersAVAudioFile and AVAudioPCMBufferNSURL *url = [[NSBundle mainBundle] URLForResource:@"groove" withExtension:@"m4a"]; // Create AVAudioFile AVAudioFile *file = [[AVAudioFile alloc] initForReading:url error:nil];

// Create AVAudioPCMBuffer AVAudioFormat *format = file.processingFormat; AVAudioFrameCount capacity = (AVAudioFrameCount)file.length;

AVAudioPCMBuffer *buffer = [[AVAudioPCMBuffer alloc] initWithPCMFormat:format frameCapacity:capacity];

// Read AVAudioFile -> AVAudioPCMBuffer [file readIntoBuffer:buffer error:nil];

AVPlayerNodeScheduling Files and BuffersImmediate File Playback[playerNode scheduleFile:audioFile atTime:nil completionHandler:nil]; [playerNode play];

Future Buffer Playback// Play audio file 5 seconds from now double sampleRate = buffer.format.sampleRate; double sampleTime = sampleRate * 5.0; AVAudioTime *futureTime = [AVAudioTime timeWithSampleTime:sampleTime atRate:sampleRate];

[playerNode scheduleBuffer:audioBuffer atTime:futureTime options:0 completionHandler:nil]; [playerNode play];

[playerNode scheduleBuffer:audioBuffer completionHandler:nil]; [playerNode play];

Immediate Buffer Playback

-Scheduling multiple buffers queues them serially

Scheduling OptionsAVAudioPlayerNodeBufferOptions

[playerNode scheduleBuffer:buffer1 atTime:nil options:0 completionHandler:nil]; [playerNode play]; [playerNode scheduleBuffer:buffer2 atTime:nil options:0 completionHandler:nil];

buffer1 buffer2

time

[playerNode scheduleBuffer:buffer2 atTime:nil options:AVAudioPlayerNodeBufferInterrupts completionHandler:nil];

-Schedule with interruption option to change this behavior

buffer1 buffer2

time

-Schedule a single looping buffer

Scheduling OptionsAVAudioPlayerNodeBufferOptions

[playerNode scheduleBuffer:buffer1 atTime:nil options:AVAudioPlayerNodeBufferLoops completionHandler:nil];

buffer1

[playerNode scheduleBuffer:buffer2 atTime:nil options:AVAudioPlayerNodeBufferInterruptsAtLoop completionHandler:nil];

-Schedule with interruption or interruption at loop

buffer1 buffer2

Audio MixingAVAudioMixerNode

-Node that mixes multiple inputs into a single output - Efficiently performs sample rate conversions - Can upmix/downmix channel counts where needed

Audio MixingAVAudioMixerNode

AVAudioMixerNodeInput 1

Input 2

-Group and process similar inputs - Simplify and improve efficiency of similar audio processing

Audio MixingUsing Submixes

AVAudioMixerNodeInput 1

Input 2

AVAudioMixerNodeInput 3

Input 4

AVAudioMixerNode(main mixer)

-AVAudioMixing Protocol: - Defines properties to be applied to an input bus of a mixer node - Source and mixer nodes conform to this protocol

Audio MixingAVAudioMixing

AVAudioOutputNodeAVAudioMixerNode

AVAudioPlayerNode

AVAudioPlayerNode

volume pan

volume pan

Input Bus 0

Input Bus 1

Audio TapsInstalling Node Taps

-Node tap pulls data off the render thread -Captures the output of a particular node

- Record data from microphone - Record data from a pre-recorded or live audio mix - Perform data visualization or analysis

-Can install one tap per output bus -Dynamically install and remove taps -Audio data returned in a block callback

Node TapsPulling Data

Node TapsInstalling a tap

AVAudioMixerNode *mixer = self.engine.mainMixerNode;

AVAudioFrameCount bufferSize = 4096; AVAudioFormat *format = [mixer outputFormatForBus:0];

[mixer installTapOnBus:0 bufferSize:bufferSize format:format block:^(AVAudioPCMBuffer *buffer, AVAudioTime *when) {

// Process AVAudioPCMBuffer

}];

Audio ProcessingApplying Audio Effects

Effect NodesDigital Signal Processing-There are two main categories of effects available:

- AVAudioUnitEffect: performs real-time audio processing - AVAudioUnitTimeEffect: performs non real-time audio processing

AVAudioUnitDelay

AVAudioUnitEQ

AVAudioUnitDistortion

AVAudioUnitReverb

AVAudioUnitEffect AVAudioUnitTimeEffect

AVAudioUnitTimePitch

AVAudioUnitVarispeed

-Delays original signal by delay time and mixes with original -Configuration parameters: - delayTime: The delay time of the input signal (up to 2 seconds) - feedback: Amount of output fed back into delay line - lowPassCutoff: Frequency past which high frequencies rolled off - wetDryMix: The blend of wet/dry signals (0% to 100%)

DelayAVAudioUnitDelay

-Multi-band equalizer and filter unit -Configuration parameters: - bands: Array of AVAudioUnitEQFilterParameters objects - globalGain: Overall gain adjustment applied to input signal (-96 to 24db)

EqualizationAVAudioUnitEQ

-Used to define the EQ parameters to be applied - Retrieved from the AVAudioUnitEQ object’s bands property

-Configuration parameters: - filterType: Parametric, Low/High Pass, Band Pass, Low/High Shelf - frequency: The center frequency or cutoff frequency - bandwidth: The width around the main frequency in octaves - gain: The gain adjustment (boost or cut) to the frequency - bypass: The bypass state

Equalization (Continued)AVAudioUnitEQFilterParameters

-Multi-stage distortion effect of original signal -Configuration presets:

- loadFactoryPreset:(AVAudioUnitDistortionPreset)preset - DrumsBitBrush, MultiBrokenSpeaker, SpeechWaves, etc

-Configuration parameters: - preGain: Gain applied to signal before distorted (-80dB to 20dB) - wetDryMix: The blend of wet/dry signals (0% to 100%)

DistortionAVAudioUnitDistortion

-Simulates the reflective qualities of a particular environment -Configuration presets:

- loadFactoryPreset:(AVAudioUnitReverbPreset)preset - Small Room, Large Hall, Cathedral, etc.

-Configuration parameters: - wetDryMix: The blend of wet/dry signals (0% to 100%)

ReverbAVAudioUnitReverb

DemoGarageMix

Using MIDIMIDI Playback

-Musical Instrument Digital Interface -Specification defining:

- Communication protocol for controlling electronic instruments - Hardware cables and connectors - Standard MIDI file format

-Extensions: - General MIDI (GM) - Downloadable Sounds (DLS)

MIDIWhat is MIDI? http://www.midi.org

-High-quality sampler instrument to play sampled sounds -Loads samples in EXS, SF2, or DLS formats

- Can additionally load and arbitrary array of sample data

-Responds to all standard MIDI messages - Note on/off, controller messages, pitch bend, etc.

-Great solution for a live performance instrument - What about playing sequences?

Sampling InstrumentAVAudioUnitSampler

-AVAudioEngine has a musicSequence property - AudioToolbox MusicSequence type

-Use the MusicPlayer and MusicSequence APIs - Attach the MusicSequence to the engine to play through Sampler

MusicSequenceCore MIDI Type

DemoEXSSampler

-Powerful new addition to AV Foundation - Simplifies low-latency, realtime audio - Great solution for music, audio, and gaming applications - Core Audio for Mortals

-Enables you to build advanced audio applications - Read and write audio files - Play and record audio using files and buffers - Add DSP effects: Reverb, Delays, etc. - Perform Stereo and 3D mixing off audio signals - MIDI playback and control over sampler instruments

SummaryAVAudioEngine