建立一个简单的均衡器 [英] Build a simple Equalizer

问题描述

我想使用AVAudioEngine制作5频段音频均衡器(60Hz，230Hz，910Hz，4kHz，14kHz).我想通过垂直滑块让用户输入每个频段的增益，并据此调整正在播放的音频.我尝试使用AVAudioUnitEQ来执行此操作，但是播放音频时没有听到任何区别.我试图对值进行硬编码以指定每个频率的增益，但是仍然无法正常工作.这是我的代码:

I would like to make a 5-band audio equalizer (60Hz, 230Hz, 910Hz, 4kHz, 14kHz) using AVAudioEngine. I would like to have the user input gain per band through a vertical slider and accordingly adjust the audio that is playing. I tried using AVAudioUnitEQ to do this, but I hear no difference when playing the audio. I tried to hardcode in values to specify a gain at each frequency, but it still does not work. Here is the code I have:

var audioEngine: AVAudioEngine = AVAudioEngine()
var equalizer: AVAudioUnitEQ!
var audioPlayerNode: AVAudioPlayerNode = AVAudioPlayerNode()
var audioFile: AVAudioFile!

// in viewDidLoad():
equalizer = AVAudioUnitEQ(numberOfBands: 5)
audioEngine.attach(audioPlayerNode)
audioEngine.attach(equalizer)
let bands = equalizer.bands
let freqs = [60, 230, 910, 4000, 14000]
audioEngine.connect(audioPlayerNode, to: equalizer, format: nil)
audioEngine.connect(equalizer, to: audioEngine.outputNode, format: nil)
for i in 0...(bands.count - 1) {
    bands[i].frequency = Float(freqs[i])
}

bands[0].gain = -10.0
bands[0].filterType = .lowShelf
bands[1].gain = -10.0
bands[1].filterType = .lowShelf
bands[2].gain = -10.0
bands[2].filterType = .lowShelf
bands[3].gain = 10.0
bands[3].filterType = .highShelf
bands[4].gain = 10.0
bands[4].filterType = .highShelf

do {
    if let filepath = Bundle.main.path(forResource: "song", ofType: "mp3") {
        let filepathURL = NSURL.fileURL(withPath: filepath)
        audioFile = try AVAudioFile(forReading: filepathURL)
        audioEngine.prepare()
        try audioEngine.start()
        audioPlayerNode.scheduleFile(audioFile, at: nil, completionHandler: nil)
        audioPlayerNode.play()
    }
} catch _ {}

由于低频增益为-10，而高频增益为10，因此播放任何媒体时都应该有非常明显的差异.但是，当媒体开始播放时，其声音与未连接任何均衡器的情况下播放的声音相同.

Since the low frequencies have a gain of -10 and the high frequencies have a gain of 10, there should be a very noticeable difference when playing any media. However, when the media starts playing, it sounds the same as if played without any equalizer attached.

我不确定为什么会这样，但是我尝试了几种不同的方法进行调试.我以为这可能是功能的顺序，所以我尝试将其切换，以便在调整所有频段之后调用audioEngine.connect，但这也没有任何区别.

I'm not sure why this is happening, but I tried several different things to debug. I thought that it might be the order of the functions so I tried switching it so that audioEngine.connect is called after adjusting all of the bands, but that did not make a difference either.

我使用AVAudioUnitTimePitch尝试了相同的代码，并且效果很好，所以我对为什么它不适用于AVAudioUnitEQ感到震惊.

I tried this same code with using an AVAudioUnitTimePitch, and it worked perfectly, so I am dumbfounded as to why it does not work with AVAudioUnitEQ.

我不想为此项目使用任何第三方库或可可豆荚，我想单独使用AVFoundation来实现.

I do not want to use any third-party libraries or cocoa pods for this project, I would like to do it using AVFoundation alone.

任何帮助将不胜感激！

谢谢.

推荐答案

AVAudioUnitEQFilterParameters 浏览文档时，我注意到除bypass之外，我已经弄乱了所有参数，并且似乎更改此标志可以修复所有问题！

AVAudioUnitEQFilterParameters Looking through the documentation, I noticed that I had messed with all of the parameters except bypass and it seems that changing this flag fixed everything!

因此，我认为这里的主要问题是，所提供的系统值(而不是程序员设置的值)一定不能绕过每个AVAudioUnitEQ频段.

So, I believe the main issue here is that each AVAudioUnitEQ band must not be bypassed by the provided system values rather than the values the programmer sets.

所以，我改变了

for i in 0...(bands.count - 1) {
    bands[i].frequency = Float(freqs[i])
}

到

for i in 0...(bands.count - 1) {
    bands[i].frequency  = Float(freqs[i])
    bands[i].bypass     = false
    bands[i].filtertype = .parametric
}

，一切开始起作用.此外，为了制作有效的均衡器，允许用户修改各个频率，每个频段的filtertype应设置为.parametric.

and everything started working. Furthermore, to make an effective equalizer that allows the user to modify individual frequencies the filtertype for each band should be set to .parametric.

我仍然不确定应该将bandwith设置为什么，但是我可能可以在线检查它，也可以将其弄乱，直到声音与其他均衡器应用程序匹配为止.

I am still unsure on what I should set the bandwith to, but I can probably check online for that or just mess with it until the sound matches a different equalizer application.

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