适当量的信封为AVAudioUnitSampler与AVFoundation [英] Proper Volume Envelopes for AVAudioUnitSampler with AVFoundation

问题描述

如何正确地创建卷信封的AVAudioUnitSampler？

基本上，我想添加一个攻击阶段，其中货量几毫秒，以避免点击变淡英寸此外，我想，这样的音量回采后淡出播放的音符添加一个释放阶段。

我做了什么至今：

我成立了一个全球性的定时器。它重新presents我的采样率。
为此，我使用的NSTimer与1个采样的间隔长度（对于44100一个样本的持续时间的采样速率是四万四千百分之一）。这样，人们不应该听到卷跳造成咔哒声。也许我需要过采样两次采样率。

定时器会调用递增masterGain只要增益低于某一阈值的功能。我递增量是通过由采样率然后通过所需的衰落时间除以这​​个数量除以在期望和电流增益的差计算。 （在下面的例子中我使用，方便阅读一个固定值）

阈值达到之后我删除计时器和停止注释。

- >我觉得这个做法是相当复杂的尤其是当我使用了一个释放阶段太

。

请查看我的例子code。我用一个UIButton触地得分触发演奏的音符。请告诉我，如果你知道一个更简单的方法来随着时间的推移/自动值建立输入/输出音量淡入淡出。

感谢

 进口的UIKit
    进口AVFoundation    一流的ViewController：UIViewController的{
    VAR引擎：AVAudioEngine！
    VAR采样：AVAudioUnitSampler！
    VAR错误：NSError？
    VAR定时器：=的NSTimer的NSTimer（）    覆盖FUNC viewDidLoad中（）{
        super.viewDidLoad（）        发动机= AVAudioEngine（）
        采样= AVAudioUnitSampler（）        engine.attachNode（采样）
        engine.connect（采样器，于：engine.mainMixerNode，格式：无）        如果发动机.startAndReturnError（安培;错误）！{
            如果让错误= {错误
                的println（发动机无法启动！）
                的println（error.localizedDescription）
            }
        }
    }    @IBAction FUNC触地（发件人：UIButton的，forEvent事件：的UIEvent）{
        sampler.startNote（66，withVelocity：66，onChannel：0）
        sampler.masterGain = -90
        定时器= NSTimer.scheduledTimerWithTimeInterval（四万四千一百分之一，目标：自我，选择：updateVolume，用户信息：无，重复：真）
    }    FUNC updateVolume（）{
        如果sampler.masterGain＆LT; = -10 {
            sampler.masterGain = sampler.masterGain + 0.1
            的println（卷更新）
        }其他{
            timer.invalidate（）
        }
    }
}
 

解决方案

哇！这是做量信封的pretty复杂的方式！

你有没有想过使得它简单一点？而不是试图控制增益控制，我只是修改实际的声音传出来。首先，我只想有我的样本存储为载体。然后，我将创造另一种载体，将重新present我的音量包络。然后，我将创造播放一个新的样本，这将仅仅是由样本和幅度向量元素相乘的元素。下面是在MATLAB的例子。

 ％装入样品
[X，FS] = audioread（'FILENAME.WAV'）;％得到你的样品长度
sampSize =长度（X）;％创建音量包络。 （我只是使用高斯窗口在这里，您可以
％与任何类型的信封的替换要，只要该值是
％0和1之间）
ampEnv = gausswin（长度（X））;你的两个向量的元素％乘法元素。
newSample = X * ampEnv。％绘制新的声音。
剧情（newSample）;
 

另外，如果你正在寻找做实时它变得更棘手一点。如果延迟不是一个巨大的问题，在这里，我建议有这将存储outcoming样品你的声音，并开始应用振幅体的方法有轻微的前瞻窗口。

How to properly create Volume Envelopes for the AVAudioUnitSampler?

Basically I want to add a Attack Phase where the volume fades in over a couple of milliseconds to avoid clicks. Additionally I want to add a release phase so that the sound volume fades out after stoping to play the note.

What I did so far:

I set up a global Timer that represents my sample rate. For this I used a NSTimer with a interval length of 1 sample (for a sample rate of 44100 one sample duration is 1/44100). That way one should not hear volume "jumps" causing "clicks". Maybe I need to oversample to twice the sample rate.

The timer would call a function that incremented the masterGain as long as the gain is below a certain threshold. The amount I incremented was calculated by dividing the difference in desired and current gain by the sample rate then dividing this amount by the desired fade time. (In the example below I use a fixed value for easy reading)

After the threshold is reached I remove the timer and stop the note.

-> I think this approach is quite complex especially when I use a release phase too.

Please check my example code. I used a UIButton touchDown to trigger the played note. Please tell me if you know a much easier way to automate a value over time/ build a volume fade in/out.

Thanks

    import UIKit
    import AVFoundation

    class ViewController: UIViewController {


    var engine: AVAudioEngine!
    var sampler: AVAudioUnitSampler!
    var error: NSError?
    var timer: NSTimer = NSTimer()

    override func viewDidLoad() {
        super.viewDidLoad()

        engine = AVAudioEngine()
        sampler = AVAudioUnitSampler()

        engine.attachNode(sampler)
        engine.connect(sampler, to: engine.mainMixerNode, format: nil)

        if !engine!.startAndReturnError(&error) {
            if let error = error {
                println("Engine could not start!")
                println(error.localizedDescription)
            }
        }
    }

    @IBAction func touchDown(sender: UIButton, forEvent event: UIEvent) {
        sampler.startNote(66, withVelocity: 66, onChannel: 0)
        sampler.masterGain = -90
        timer = NSTimer.scheduledTimerWithTimeInterval (1/44100, target: self, selector: "updateVolume", userInfo: nil, repeats: true)
    }

    func updateVolume() {
        if sampler.masterGain <= -10 {
            sampler.masterGain = sampler.masterGain + 0.1
            println("volume updated")
        } else {
            timer.invalidate()
        }
    }
}

解决方案

Wow! That's a pretty complicated way of doing volume envelopes!

Have you thought about making it a bit simpler? Rather than trying to control the gain control, I would just modify the actual audio coming out. First I would just have my sample stored as a vector. Then, I would create another vector that would represent my volume envelope. Then, I would create a new sample for playback, which would just be an element by element multiplication of the sample and amplitude vectors. Here's an example in matlab.

%Load your sample
[x, Fs] = audioread('filename.wav');

%get the length of your sample
sampSize = length(x); 

%Create volume envelope. (Im just using a Gaussian window here. You can 
%replace it with any type of envelope you want so long as the values are
%between 0 and 1.)
ampEnv = gausswin(length(x)); 

%Multiply element by element of your two vectors. 
newSample = x.*ampEnv; 

%Plot your new sound. 
plot(newSample); 

Alternatively, if you're looking to do it in real time it becomes a bit more tricky. If delay isn't a massive issue here, I suggest having a slight lookahead window which would store the outcoming samples of you sounds and begin applying amplitude volume methods there.

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