Ios 使用AVAudioEngine进行液位测量

我刚刚在

AVAudioEngine

上观看了WWDC视频（练习中的502节

AVAudioEngine

），我非常兴奋能制作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输出进行电平监控

有人能帮忙吗？明确地说，我说的是监视当前输入信号（并在UI中显示），而不是通道/轨道的输入/输出音量设置

---

我知道你可以用

AVAudioRecorder

来实现这一点，但这不是

AVAudioEngine

所需要的

AVAudioNode

。

尝试在主混音器上安装一个水龙头，然后通过设置帧长来加快速度，然后读取样本并获得平均值，类似这样：

顶部导入框架

那么下面的内容也一样>>

然后，获取所需的目标值

要获得峰值，请使用vDSP_maxmgv而不是vDSP_meamgv

---

---

LEVEL_LOWPASS_TRIG是一个值介于0.0到1.0之间的简单过滤器，如果设置为0.0，则会过滤所有值，而不会获得任何数据。如果将其设置为1.0，则会产生太多噪音。基本上，值越高，数据的变化就越大。似乎0.10到0.30之间的值对于大多数应用程序都是好的。

我发现了另一个有点奇怪的解决方案，但效果非常好，比tap好得多。混音器没有AudioUnit，但如果您将其转换为AvaudioNode，则可以获得AudioUnit并使用iOS的计量设备。以下是如何：

要启用或禁用计量，请执行以下操作：

- (void)setMeteringEnabled:(BOOL)enabled;
{
    UInt32 on = (enabled)?1:0;
    AVAudioIONode *node = (AVAudioIONode*)self.engine.mainMixerNode;
    OSStatus err = AudioUnitSetProperty(node.audioUnit, kAudioUnitProperty_MeteringMode, kAudioUnitScope_Output, 0, &on, sizeof(on));
}

要更新仪表，请执行以下操作：

- (void)updateMeters;
{
    AVAudioIONode *node = (AVAudioIONode*)self.engine.mainMixerNode;

    AudioUnitParameterValue level;
    AudioUnitGetParameter(node.audioUnit, kMultiChannelMixerParam_PostAveragePower, kAudioUnitScope_Output, 0, &level);

    self.averagePowerForChannel1 = self.averagePowerForChannel0 = level;
    if(self.numberOfChannels>1)
    {
        err = AudioUnitGetParameter(node.audioUnit, kMultiChannelMixerParam_PostAveragePower+1, kAudioUnitScope_Output, 0, &level);
    }
}

---

法哈德·马勒克普尔回答的等效Swift 3代码

顶部导入框架

全球申报

在需要的地方使用以下代码

计算

#导入
#进口
#进口
#进口
#进口
#进口
@接口录音：NSObject{
}
@属性（非原子）AVAudioEngine*记录引擎；
@属性float averagePowerForChannel0；
@信道1的属性浮点平均功率；
@财产浮动通道数；
@属性NSLevelIndicator*levelIndicator；
-（BOOL）recordToFile:（NSString*）文件路径；
@结束

Swift 5+

下载以上项目并在您的项目中复制“micromic.swift”类

在项目中复制并粘贴这些定位代码：

import AVFoundation

private var mic = MicrophoneMonitor(numberOfSamples: 1)
private var timer:Timer!

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("sound level:", normalizeSoundLevel(level: mic.soundSamples.first!))
}

private func normalizeSoundLevel(level: Float) -> CGFloat {
    let level = max(0.2, CGFloat(level) + 50) / 2 // between 0.1 and 25
    return CGFloat(level * (300 / 25)) // scaled to max at 300 (our height of our bar)
}

---

3.开瓶啤酒庆祝一下

LEVEL_LOWPASS_TRIG使用的值（或范围）是多少？要使用vDSP_meamgv，请使用Apple的高性能数学框架进行“导入加速”。您可以在Github中发布完整的工作示例吗？@apocolipse我也不知道该放什么。。。电平低通触发=0.01对我有效。这是最好的选择。我对Swift也做了同样的事情，所以这个ObjC语法在另一个应用程序上对我来说是一个救命稻草。它可以根据音量的不同视觉表现进行调整：波形字符、简单的音量条或音量相关的透明度（褪色的麦克风图标等）。您是否有此代码的工作示例？这显示了整个循环。。如何实例化AudioEngine等。noob问题-如果节点设置在通道0上，为什么有两个通道？对于@omarojo。下面是使用其他两个答案组合的工作代码。要使用的.h文件，只需调用newAudioRecord=[AudioRecord new]；newAudioRecord.levelIndicator=self.audioLevelIndicator；--实验性的（但不是很好的）[newAudioRecord recordToFile:fullFilePath_Name]；[newAudioRecord.recordEngine stop]；[newAudioRecord.recordEngine重置]；newAudioRecord.recordEngine暂停]；要继续：[newAudioRecord.recordEngine startAndReturnError:NULL]；这是在不断地将音频重新编码到文件中吗？似乎效率不高。这是我找到的唯一方法！

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

- (void)setMeteringEnabled:(BOOL)enabled;
{
    UInt32 on = (enabled)?1:0;
    AVAudioIONode *node = (AVAudioIONode*)self.engine.mainMixerNode;
    OSStatus err = AudioUnitSetProperty(node.audioUnit, kAudioUnitProperty_MeteringMode, kAudioUnitScope_Output, 0, &on, sizeof(on));
}

- (void)updateMeters;
{
    AVAudioIONode *node = (AVAudioIONode*)self.engine.mainMixerNode;

    AudioUnitParameterValue level;
    AudioUnitGetParameter(node.audioUnit, kMultiChannelMixerParam_PostAveragePower, kAudioUnitScope_Output, 0, &level);

    self.averagePowerForChannel1 = self.averagePowerForChannel0 = level;
    if(self.numberOfChannels>1)
    {
        err = AudioUnitGetParameter(node.audioUnit, kMultiChannelMixerParam_PostAveragePower+1, kAudioUnitScope_Output, 0, &level);
    }
}

import Accelerate

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

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)
}

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)
            }
    }

#define LEVEL_LOWPASS_TRIG .3

#import "AudioRecorder.h"





@implementation AudioRecord


-(id)init {
     self = [super init];
     self.recordEngine = [[AVAudioEngine alloc] init];

     return self;
}


 /**  ----------------------  Snippet Stackoverflow.com not including Audio Level Meter    ---------------------     **/


-(BOOL)recordToFile:(NSString*)filePath {

     NSURL *fileURL = [NSURL fileURLWithPath:filePath];

     const Float64 sampleRate = 44100;

     AudioStreamBasicDescription aacDesc = { 0 };
     aacDesc.mSampleRate = sampleRate;
     aacDesc.mFormatID = kAudioFormatMPEG4AAC; 
     aacDesc.mFramesPerPacket = 1024;
     aacDesc.mChannelsPerFrame = 2;

     ExtAudioFileRef eaf;

     OSStatus err = ExtAudioFileCreateWithURL((__bridge CFURLRef)fileURL, kAudioFileAAC_ADTSType, &aacDesc, NULL, kAudioFileFlags_EraseFile, &eaf);
     assert(noErr == err);

     AVAudioInputNode *input = self.recordEngine.inputNode;
     const AVAudioNodeBus bus = 0;

     AVAudioFormat *micFormat = [input inputFormatForBus:bus];

     err = ExtAudioFileSetProperty(eaf, kExtAudioFileProperty_ClientDataFormat, sizeof(AudioStreamBasicDescription), micFormat.streamDescription);
     assert(noErr == err);

     [input installTapOnBus:bus bufferSize:1024 format:micFormat block:^(AVAudioPCMBuffer *buffer, AVAudioTime *when) {
       const AudioBufferList *abl = buffer.audioBufferList;
       OSStatus err = ExtAudioFileWrite(eaf, buffer.frameLength, abl);
       assert(noErr == err);


       /**  ----------------------  Snippet from stackoverflow.com in different context  ---------------------     **/


       UInt32 inNumberFrames = buffer.frameLength;
       if(buffer.format.channelCount>0) {
         Float32* samples = (Float32*)buffer.floatChannelData[0]; 
         Float32 avgValue = 0;
         vDSP_maxv((Float32*)samples, 1.0, &avgValue, inNumberFrames);
         self.averagePowerForChannel0 = (LEVEL_LOWPASS_TRIG*((avgValue==0)?
                                  -100:20.0*log10f(avgValue))) + ((1- LEVEL_LOWPASS_TRIG)*self.averagePowerForChannel0) ;
         self.averagePowerForChannel1 = self.averagePowerForChannel0;
       }

       dispatch_async(dispatch_get_main_queue(), ^{

         self.levelIndicator.floatValue=self.averagePowerForChannel0;

       });     


       /**  ---------------------- End of Snippet from stackoverflow.com in different context  ---------------------     **/

     }];

     BOOL startSuccess;
     NSError *error;

     startSuccess = [self.recordEngine startAndReturnError:&error]; 
     return startSuccess;
}



@end

#import <Foundation/Foundation.h>
#import <AVFoundation/AVFoundation.h>
#import <AudioToolbox/ExtendedAudioFile.h>
#import <CoreAudio/CoreAudio.h>
#import <Accelerate/Accelerate.h>
#import <AppKit/AppKit.h>

@interface AudioRecord : NSObject {

}

@property (nonatomic) AVAudioEngine *recordEngine;


@property float averagePowerForChannel0;
@property float averagePowerForChannel1;
@property float numberOfChannels;
@property NSLevelIndicator * levelIndicator;


-(BOOL)recordToFile:(NSString*)filePath;

@end

import AVFoundation

private var mic = MicrophoneMonitor(numberOfSamples: 1)
private var timer:Timer!

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("sound level:", normalizeSoundLevel(level: mic.soundSamples.first!))
}

private func normalizeSoundLevel(level: Float) -> CGFloat {
    let level = max(0.2, CGFloat(level) + 50) / 2 // between 0.1 and 25
    return CGFloat(level * (300 / 25)) // scaled to max at 300 (our height of our bar)
}