使用AVAudioEngine进行电平测量

Question

我刚刚在AVAudioEngine上观看了WWDC视频(练习中的Session 502 AVAudioEngine )，我非常兴奋能做一个基于这项技术的应用程序。

我还不知道如何对麦克风输入或混音器的输出进行电平监控。

有人能帮上忙吗？为了清楚起见，我说的是监控当前输入信号(并在UI中显示)，而不是声道/音轨的输入/输出音量设置。

我知道你可以用AVAudioRecorder做到这一点，但这不是AVAudioEngine所要求的AVAudioNode。

Answer 1

尝试在主搅拌器上安装一个水龙头，然后通过设置帧长度来使其更快，然后阅读示例并获得平均值，类似于：

顶部的

导入框架

#import <Accelerate/Accelerate.h>

add属性

@property float averagePowerForChannel0;
@property float averagePowerForChannel1;

，然后在same>>下面

self.mainMixer = [self.engine mainMixerNode];
[self.mainMixer installTapOnBus:0 bufferSize:1024 format:[self.mainMixer outputFormatForBus:0] block:^(AVAudioPCMBuffer * _Nonnull buffer, AVAudioTime * _Nonnull when) {
    [buffer setFrameLength:1024];
    UInt32 inNumberFrames = buffer.frameLength;

    if(buffer.format.channelCount>0)
    {
        Float32* samples = (Float32*)buffer.floatChannelData[0];
        Float32 avgValue = 0;

        vDSP_meamgv((Float32*)samples, 1, &avgValue, inNumberFrames);
        self.averagePowerForChannel0 = (LEVEL_LOWPASS_TRIG*((avgValue==0)?-100:20.0*log10f(avgValue))) + ((1-LEVEL_LOWPASS_TRIG)*self.averagePowerForChannel0) ;
        self.averagePowerForChannel1 = self.averagePowerForChannel0;
    }

    if(buffer.format.channelCount>1)
    {
        Float32* samples = (Float32*)buffer.floatChannelData[1];
        Float32 avgValue = 0;

        vDSP_meamgv((Float32*)samples, 1, &avgValue, inNumberFrames);
        self.averagePowerForChannel1 = (LEVEL_LOWPASS_TRIG*((avgValue==0)?-100:20.0*log10f(avgValue))) + ((1-LEVEL_LOWPASS_TRIG)*self.averagePowerForChannel1) ;
    }
}];

然后，获取所需的目标值

NSLog(@"===test===%.2f", self.averagePowerForChannel1);

要获取峰值，请使用vDSP_maxmgv而不是vDSP_meamgv。

LEVEL_LOWPASS_TRIG是一个简单的筛选器，值在0.0到1.0之间，如果设置为0.0，您将过滤所有值，并且不会获得任何数据。如果将其设置为1.0，则会获得太多噪波。基本上，值越高，数据的变化就越大。对于大多数应用程序来说，0.10到0.30之间的值似乎是很好的。

Answer 2

相当于'Farhad‘答案的Swift 3代码

顶部的

导入框架

import Accelerate

全局声明

private var audioEngine: AVAudioEngine?
    private var averagePowerForChannel0: Float = 0
    private var averagePowerForChannel1: Float = 0
let LEVEL_LOWPASS_TRIG:Float32 = 0.30

在您需要的地方使用下面的代码

let inputNode = audioEngine!.inputNode//since i need microphone audio level i have used `inputNode` otherwise you have to use `mainMixerNode`
let recordingFormat: AVAudioFormat = inputNode!.outputFormat(forBus: 0)
 inputNode!.installTap(onBus: 0, bufferSize: 1024, format: recordingFormat) {[weak self] (buffer:AVAudioPCMBuffer, when:AVAudioTime) in
                guard let strongSelf = self else {
                    return
                }
                strongSelf.audioMetering(buffer: buffer)
}

计算

private func audioMetering(buffer:AVAudioPCMBuffer) {
            buffer.frameLength = 1024
            let inNumberFrames:UInt = UInt(buffer.frameLength)
            if buffer.format.channelCount > 0 {
                let samples = (buffer.floatChannelData![0])
                var avgValue:Float32 = 0
                vDSP_meamgv(samples,1 , &avgValue, inNumberFrames)
                var v:Float = -100
                if avgValue != 0 {
                    v = 20.0 * log10f(avgValue)
                }
                self.averagePowerForChannel0 = (self.LEVEL_LOWPASS_TRIG*v) + ((1-self.LEVEL_LOWPASS_TRIG)*self.averagePowerForChannel0)
                self.averagePowerForChannel1 = self.averagePowerForChannel0
            }

            if buffer.format.channelCount > 1 {
                let samples = buffer.floatChannelData![1]
                var avgValue:Float32 = 0
                vDSP_meamgv(samples, 1, &avgValue, inNumberFrames)
                var v:Float = -100
                if avgValue != 0 {
                    v = 20.0 * log10f(avgValue)
                }
                self.averagePowerForChannel1 = (self.LEVEL_LOWPASS_TRIG*v) + ((1-self.LEVEL_LOWPASS_TRIG)*self.averagePowerForChannel1)
            }
    }

Answer 3

Swift 5+

I got help from this project.

在项目上方下载

1. 并将'Microphone.swift‘类复制到您的项目中。
2. copy将以下回收代码粘贴到您的项目中：

导入AVFoundation私有变量麦克风= MicrophoneMonitor(numberOfSamples: 1)私有变量定时器:定时器！override func viewDidLoad() { super.viewDidLoad() timer = Timer.scheduledTimer(timeInterval: 0.1，target: self，selector：#selector(startMonitoring)，userInfo: nil，repeats: true) timer.fire() } @objc func startMonitoring() {print(“声音级别：”，normalizeSoundLevel(级别: mic.soundSamples.first!)) }私有函数normalizeSoundLevel(级别:浮点) -> CGFloat { let level = max(0.2，CGFloat(级别)+ 50) /2 //在0.1和25之间返回CGFloat(级别* (300 / 25)) //在300 (我们的条形高度)时缩放到最大}

3.开瓶啤酒庆祝一下吧！