Tap Mic Input Using AVAudioEngine in Swift - ios

Question

I'm really excited about the new AVAudioEngine. It seems like a good API wrapper around audio unit. Unfortunately the documentation is so far nonexistent, and I'm having problems getting a simple graph to work.
Using the following simple code to set up an audio engine graph, the tap block is never called. It mimics some of the sample code floating around the web, though those also did not work.
let inputNode = audioEngine.inputNode
var error: NSError?
let bus = 0
inputNode.installTapOnBus(bus, bufferSize: 2048, format: inputNode.inputFormatForBus(bus)) {
(buffer: AVAudioPCMBuffer!, time: AVAudioTime!) -> Void in
println("sfdljk")
}
audioEngine.prepare()
if audioEngine.startAndReturnError(&error) {
println("started audio")
} else {
if let engineStartError = error {
println("error starting audio: \(engineStartError.localizedDescription)")
}
}
All I'm looking for is the raw pcm buffer for analysis. I don't need any effects or output. According to the WWDC talk "502 Audio Engine in Practice", this setup should work.
Now if you want to capture data from the input node, you can install a node tap and we've talked about that.
But what's interesting about this particular example is, if I wanted to work with just the input node, say just capture data from the microphone and maybe examine it, analyze it in real time or maybe write it out to file, I can directly install a tap on the input node.
And the tap will do the work of pulling the input node for data, stuffing it in buffers and then returning that back to the application.
Once you have that data you can do whatever you need to do with it.
Here are some links I tried:
http://hondrouthoughts.blogspot.com/2014/09/avfoundation-audio-monitoring.html
http://jamiebullock.com/post/89243252529/live-coding-audio-with-swift-playgrounds (SIGABRT in playground on startAndReturnError)
Edit: This is the implementation based on Thorsten Karrer's suggestion. It unfortunately does not work.
class AudioProcessor {
let audioEngine = AVAudioEngine()
init(){
let inputNode = audioEngine.inputNode
let bus = 0
var error: NSError?
inputNode.installTapOnBus(bus, bufferSize: 2048, format:inputNode.inputFormatForBus(bus)) {
(buffer: AVAudioPCMBuffer!, time: AVAudioTime!) -> Void in
println("sfdljk")
}
audioEngine.prepare()
audioEngine.startAndReturnError(nil)
println("started audio")
}
}

Answer 1

It might be the case that your AVAudioEngine is going out of scope and is released by ARC ("If you liked it then you should have put retain on it...").
The following code (engine is moved to an ivar and thus sticks around) fires the tap:
class AppDelegate: NSObject, NSApplicationDelegate {
let audioEngine = AVAudioEngine()
func applicationDidFinishLaunching(aNotification: NSNotification) {
let inputNode = audioEngine.inputNode
let bus = 0
inputNode.installTapOnBus(bus, bufferSize: 2048, format: inputNode.inputFormatForBus(bus)) {
(buffer: AVAudioPCMBuffer!, time: AVAudioTime!) -> Void in
println("sfdljk")
}
audioEngine.prepare()
audioEngine.startAndReturnError(nil)
}
}
(I removed the error handling for brevity)

Answer 2

UPDATED: I have implemented a complete working example of Recording mic input, applying some effects (reverbs, delay, distortion) at runtime, and save all these effects to an output file.
var engine = AVAudioEngine()
var distortion = AVAudioUnitDistortion()
var reverb = AVAudioUnitReverb()
var audioBuffer = AVAudioPCMBuffer()
var outputFile = AVAudioFile()
var delay = AVAudioUnitDelay()
//Initialize the audio engine
func initializeAudioEngine() {
engine.stop()
engine.reset()
engine = AVAudioEngine()
isRealTime = true
do {
try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayAndRecord)
let ioBufferDuration = 128.0 / 44100.0
try AVAudioSession.sharedInstance().setPreferredIOBufferDuration(ioBufferDuration)
} catch {
assertionFailure("AVAudioSession setup error: \(error)")
}
let fileUrl = URLFor("/NewRecording.caf")
print(fileUrl)
do {
try outputFile = AVAudioFile(forWriting: fileUrl!, settings: engine.mainMixerNode.outputFormatForBus(0).settings)
}
catch {
}
let input = engine.inputNode!
let format = input.inputFormatForBus(0)
//settings for reverb
reverb.loadFactoryPreset(.MediumChamber)
reverb.wetDryMix = 40 //0-100 range
engine.attachNode(reverb)
delay.delayTime = 0.2 // 0-2 range
engine.attachNode(delay)
//settings for distortion
distortion.loadFactoryPreset(.DrumsBitBrush)
distortion.wetDryMix = 20 //0-100 range
engine.attachNode(distortion)
engine.connect(input, to: reverb, format: format)
engine.connect(reverb, to: distortion, format: format)
engine.connect(distortion, to: delay, format: format)
engine.connect(delay, to: engine.mainMixerNode, format: format)
assert(engine.inputNode != nil)
isReverbOn = false
try! engine.start()
}
//Now the recording function:
func startRecording() {
let mixer = engine.mainMixerNode
let format = mixer.outputFormatForBus(0)
mixer.installTapOnBus(0, bufferSize: 1024, format: format, block:
{ (buffer: AVAudioPCMBuffer!, time: AVAudioTime!) -> Void in
print(NSString(string: "writing"))
do{
try self.outputFile.writeFromBuffer(buffer)
}
catch {
print(NSString(string: "Write failed"));
}
})
}
func stopRecording() {
engine.mainMixerNode.removeTapOnBus(0)
engine.stop()
}
I hope this might help you. Thanks!

Answer 3

The above answer didn't work for me but the following did. I'm installing a tap on a mixer node.
mMixerNode?.installTapOnBus(0, bufferSize: 4096, format: mMixerNode?.outputFormatForBus(0),
{
(buffer: AVAudioPCMBuffer!, time:AVAudioTime!) -> Void in
NSLog("tapped")
}
)

Answer 4

nice topic
hi brodney
in your topic i find my solution . here is similar topic Generate AVAudioPCMBuffer with AVAudioRecorder
see lecture Wwdc 2014 502 - AVAudioEngine in Practice capture microphone => in 20 min create buffer with tap code => in 21 .50
here is swift 3 code
#IBAction func button01Pressed(_ sender: Any) {
let inputNode = audioEngine.inputNode
let bus = 0
inputNode?.installTap(onBus: bus, bufferSize: 2048, format: inputNode?.inputFormat(forBus: bus)) {
(buffer: AVAudioPCMBuffer!, time: AVAudioTime!) -> Void in
var theLength = Int(buffer.frameLength)
print("theLength = \(theLength)")
var samplesAsDoubles:[Double] = []
for i in 0 ..< Int(buffer.frameLength)
{
var theSample = Double((buffer.floatChannelData?.pointee[i])!)
samplesAsDoubles.append( theSample )
}
print("samplesAsDoubles.count = \(samplesAsDoubles.count)")
}
audioEngine.prepare()
try! audioEngine.start()
}
to stop audio
func stopAudio()
{
let inputNode = audioEngine.inputNode
let bus = 0
inputNode?.removeTap(onBus: bus)
self.audioEngine.stop()
}