Filtering audio in AudioKit - ios

Question

What i need to do:
record audio file;
as it's record from iPhone/iPad microphone it can be quiet, so i need to filter it to make it louder;
save filtered record;
I'm new in audio programming, but as I understand so far I need "All Pass" filter (if not please correct me).
For this task I've found two libs: Novocaine and AudioKit, but Novocaine written in C, so it's harder to implement it in swift, and I decided to use AudioKit, but I didn't found "All Pass" filter there.
Does anybody know how to implement it in AudioKit and save filtered file? Thank you!

Answer 1

You have a few choices, for musical recordings I recommend AKBooster as it purely boosts the audio, you have to be careful how much you boost, otherwise you might cause clipping.
For spoken word audio I recommend AKPeakLimiter. It will give you the maximum volume without clipping. Set the attackTime and decayTime to lower values to hear a more pronounced effect.
The values of the sliders won't represent the values of the parameters until you move them.
import UIKit
import AudioKit
class ViewController: UIViewController {
let mic = AKMicrophone()
let boost = AKBooster()
let limiter = AKPeakLimiter()
override func viewDidLoad() {
super.viewDidLoad()
mic >>> boost >>> limiter
AudioKit.output = limiter
AudioKit.start()
let inset: CGFloat = 10.0
let width = view.bounds.width - inset * 2
for i in 0..<4 {
let y = CGFloat(100 + i * 50)
let slider = UISlider(frame: CGRect(x: inset, y: y, width: width, height: 30))
slider.tag = i
slider.addTarget(self, action: #selector(sliderAction(slider:)), for: .valueChanged)
view.addSubview(slider)
}
boost.gain = 1
}
#objc func sliderAction(slider: UISlider) {
switch slider.tag {
case 0:
boost.gain = slider.value * 40
case 1:
limiter.preGain = slider.value * 40
case 2:
limiter.attackTime = max(0.001, slider.value * 0.03)
case 4:
limiter.decayTime = max(0.001, slider.value * 0.06)
default: break
}
}
}