Question

我试图将音频录制到文件（工作），然后对该文件中的数据进行采样（给出奇怪的结果）。仅供参考，我大致遵循此代码...... Extracting Amplitude Data from Linear PCM on the iPhone

我注意到了一些不同的结果。为简单起见，假设记录时间固定为1秒。

当采样高达8,000个样本/秒时，可变阵列（见代码）将列出8,000个条目，但只有前4,000个具有真实数据，最后4,000个点是相同的数值（确切数字）价值因运行而异。
与问题＃1有些相关。当采样超过8,000个样本/秒时，前半部分样本（例如，10,000个样本中的5,000个，每秒10,000个样本，1秒）将看起来像真实数据，而后半部分的值将被固定为某个值（同样，这个确切的值会随着运行而变化）。从我的调试窗口看下面的代码片段，第一个数字是packetIndex，第二个数字是缓冲区值。

4996：-137

4997：1043

4998：-405

4999：-641

5000：195 注意从随机数据切换到5k的常量值，对于10k样本文件

5001：195

5002：195

5003：195

5004：195

3。当麦克风收听扬声器播放1kHz正弦音并靠近并以每秒40,000个样本采样该音时，在电子表格中绘制的结果数据显示信号约为2kHz或两倍。

我在这里做错了什么想法？

这是我从麦克风录制音频的设置工作......

-(void) initAudioSession {
//    setup av session
    AVAudioSession *audioSession = [AVAudioSession sharedInstance];
    [audioSession setCategory:AVAudioSessionCategoryPlayAndRecord error:nil];
    [audioSession setActive:YES error: nil];
    NSLog(@"audio session initiated");
//    settings for the recorded file
    NSDictionary *recordSettings = [[NSDictionary alloc] initWithObjectsAndKeys:
                                    [NSNumber numberWithFloat:SAMPLERATE],AVSampleRateKey,
                                    [NSNumber numberWithInt:kAudioFormatLinearPCM],AVFormatIDKey,
                                    [NSNumber numberWithInt:1],AVNumberOfChannelsKey,
                                    [NSNumber numberWithInt:16],AVEncoderBitRateKey,
                                    [NSNumber numberWithInt:AVAudioQualityMax],AVEncoderAudioQualityKey, nil];
//    setup file name and location
    NSString *docDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    fileURL = [NSURL fileURLWithPath:[docDir stringByAppendingPathComponent:@"input.caf"]];//caf or aif?
//    initialize my new audio recorder
    newAudioRecorder = [[AVAudioRecorder alloc] initWithURL:fileURL settings:recordSettings error:nil];
//    show file location so i can check it with some player
    NSLog(@"file path = %@",fileURL);
//    check if the recorder exists, if so prepare the recorder, if not tell me in debug window
    if (newAudioRecorder) {
        [newAudioRecorder setDelegate:self];
        [newAudioRecorder prepareToRecord];
        [self.setupStatus setText:[NSString stringWithFormat:@"recorder ready"]];
    }else{
        NSLog(@"error setting up recorder");
    }
}

这是我加载录制文件并抓取数据的代码......

//loads file and go thru values, converts data to be put into an NSMutableArray
-(void)readingRainbow{
    //    get audio file and put into a file ID
    AudioFileID fileID;
    AudioFileOpenURL((__bridge CFURLRef)fileURL, kAudioFileReadPermission, kAudioFileCAFType /*kAudioFileAIFFType*/ , &fileID);
    //    get number of packets of audio contained in file
//    instead of getting packets, i just set them to the duration times the sample rate i set
//    not sure if this is a valid approach
    UInt64 totalPacketCount = SAMPLERATE*timer;
    //    get size of each packet, is this valid?
    UInt32 maxPacketSizeInBytes = sizeof(SInt32);
    //    setup to extract audio data
    UInt32 totPack32 = SAMPLERATE*timer;
    UInt32 ioNumBytes = totPack32*maxPacketSizeInBytes;
    SInt16 *outBuffer = malloc(ioNumBytes);
    memset(outBuffer, 0, ioNumBytes);
    //    setup array to put buffer samples in
    readArray = [[NSMutableArray alloc] initWithObjects: nil];
    NSNumber *arrayData;
    SInt16 data;
    int data2;


//    this may be where i need help as well....
    //    process every packet
    for (SInt64 packetIndex = 0; packetIndex<totalPacketCount; packetIndex++) {
// method description for reference..
//        AudioFileReadPackets(<#AudioFileID inAudioFile#>, <#Boolean inUseCache#>, <#UInt32 *outNumBytes#>,
//        <#AudioStreamPacketDescription *outPacketDescriptions#>, <#SInt64 inStartingPacket#>,
//        <#UInt32 *ioNumPackets#>, <#void *outBuffer#>)
//        extract packet data, not sure if i'm setting this up properly
        AudioFileReadPackets(fileID, false, &ioNumBytes, NULL, packetIndex, &totPack32, outBuffer);
//        get buffer data and pass into mutable array
        data = outBuffer[packetIndex];
        data2=data;
        arrayData = [[NSNumber alloc] initWithInt:data2];
        [readArray addObject:arrayData];
//        printf("%lld:%d\n",packetIndex,data);
        printf("%d,",data);

    }

另外，我使用这种方法启动录音机......

[newAudioRecorder recordForDuration:timer];

Thots？我是一个菜鸟，所以非常感谢任何信息！

Answer 1

您可能正在录制16位样本，但尝试从文件数据中读取32位样本，因此只能找到一半的样本（其余样本可能是垃圾）。

AudioFileReadPackets提供奇怪的数据

1 个答案: