[英]AudioFileReadPackets gives strange data
我正在尝试将音频记录到一个文件(正在工作),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... 从iPhone上的Linear PCM提取幅度数据
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。
当以每秒8,000个样本的速度采样时,可变数组(请参见代码)将列出8,000个条目,但是只有前4,000个具有真实数据,最后4,000个点是相同的数字值(确切的数字值从运行到-跑)。
与问题1有关。 当采样速度超过8,000个样本/秒时,样本的前半部分(例如10,000个样本/秒的10,0000个样本集中的5,000个,持续1秒)看起来像真实数据,而集合的后半部分的值将固定为某个值(同样,该精确值因运行而异)。 从我的调试窗口中看到以下代码片段,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请注意,对于10k样本文件,从5k的随机数据切换到恒定值
5001:195
5002:195
5003:195
5004:195
3。 当麦克风让扬声器听近距离播放1kHz正弦波的扬声器并以每秒40,000个样本的速度采样此音频时,在电子表格中绘制时所得的数据显示信号约为2kHz或两倍。
有什么想法我可能在这里做错了吗?
这是我录制麦克风音频的设置工作...
-(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");
}
}
这是我的代码,用于加载记录的文件和获取数据...
//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,我正在使用这种方法来启动记录器...
[newAudioRecorder recordForDuration:timer];
Thots? 我是菜鸟,因此非常感谢您提供任何信息!
您可能正在记录16位样本,但是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)。
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