在iphone上播放蜂鳴聲與頻率和分貝有關

#import <AudioToolbox/AudioToolbox.h> 
#define TONE_SAMPLERATE 44100. 

@interface Tone : NSObject { 
    AudioQueueRef queue; 
    AudioQueueBufferRef buffer; 
    BOOL rebuildBuffer; 
} 
@property (nonatomic, assign) NSUInteger frequency; 
@property (nonatomic, assign) CGFloat dB; 

- (void)play; 
- (void)pause; 
@end 


@implementation Tone 
@synthesize dB=_dB,frequency=_frequency; 

void handleBuffer(void *inUserData, 
        AudioQueueRef inAQ, 
        AudioQueueBufferRef inBuffer); 

#pragma mark - Initialization and deallocation - 

- (id)init 
{ 
    if ((self=[super init])) { 

     _dB=0.; 
     _frequency=440; 
     rebuildBuffer=YES; 

     // TO DO: handle AudioQueueXYZ's failures!! 

     // create a descriptor containing a LPCM, mono, float format 
     AudioStreamBasicDescription desc; 

     desc.mSampleRate=TONE_SAMPLERATE; 
     desc.mFormatID=kAudioFormatLinearPCM; 
     desc.mFormatFlags=kLinearPCMFormatFlagIsFloat; 
     desc.mBytesPerPacket=sizeof(float); 
     desc.mFramesPerPacket=1; 
     desc.mBytesPerFrame=sizeof(float); 
     desc.mChannelsPerFrame=1; 
     desc.mBitsPerChannel=8*sizeof(float); 

     // create a new queue 
     AudioQueueNewOutput(&desc, 
          &handleBuffer, 
          self, 
          CFRunLoopGetCurrent(), 
          kCFRunLoopCommonModes, 
          0, 
          &queue); 

     // and its buffer, ready to hold 1" of data 
     AudioQueueAllocateBuffer(queue, 
           sizeof(float)*TONE_SAMPLERATE, 
           &buffer); 

     // create the buffer and enqueue it 
     handleBuffer(self, queue, buffer); 

    } 
    return self; 
} 

- (void)dealloc 
{ 
    AudioQueueStop(queue, YES); 
    AudioQueueFreeBuffer(queue, buffer); 
    AudioQueueDispose(queue, YES); 

    [super dealloc]; 
} 

#pragma mark - Main function - 

void handleBuffer(void *inUserData, 
       AudioQueueRef inAQ, 
       AudioQueueBufferRef inBuffer) { 

    // this function takes care of building the buffer and enqueuing it. 

    // cast inUserData type to Tone 
    Tone *tone=(Tone *)inUserData; 

    // check if the buffer must be rebuilt 
    if (tone->rebuildBuffer) { 

     // precompute some useful qtys 
     float *data=inBuffer->mAudioData; 
     NSUInteger max=inBuffer->mAudioDataBytesCapacity/sizeof(float); 

     // multiplying the argument by 2pi changes the period of the cosine 
     // function to 1s (instead of 2pi). then we must divide by the sample 
     // rate to get TONE_SAMPLERATE samples in one period. 
     CGFloat unit=2.*M_PI/TONE_SAMPLERATE; 
     // this is the amplitude converted from dB to a linear scale 
     CGFloat amplitude=pow(10., tone.dB*.05); 

     // loop and simply set data[i] to the value of cos(...) 
     for (NSUInteger i=0; i<max; ++i) 
      data[i]=(float)(amplitude*cos(unit*(CGFloat)(tone.frequency*i))); 

     // inform the queue that we have filled the buffer 
     inBuffer->mAudioDataByteSize=sizeof(float)*max; 

     // and set flag 
     tone->rebuildBuffer=NO; 
    } 

    // reenqueue the buffer 
    AudioQueueEnqueueBuffer(inAQ, 
          inBuffer, 
          0, 
          NULL); 

    /* TO DO: the transition between two adjacent buffers (the same one actually) 
       generates a "tick", even if the adjacent buffers represent a continuous signal. 
       maybe using two buffers instead of one would fix it. 
    */ 
} 

#pragma - Properties and methods - 

- (void)play 
{ 
    // generate an AudioTimeStamp with "0" simply! 
    // (copied from FillOutAudioTimeStampWithSampleTime) 

    AudioTimeStamp time; 

    time.mSampleTime=0.; 
    time.mRateScalar=0.; 
    time.mWordClockTime=0.; 
    memset(&time.mSMPTETime, 0, sizeof(SMPTETime)); 
    time.mFlags = kAudioTimeStampSampleTimeValid; 

    // TO DO: maybe it could be useful to check AudioQueueStart's return value 
    AudioQueueStart(queue, &time); 
} 

- (void)pause 
{ 
    // TO DO: maybe it could be useful to check AudioQueuePause's return value 
    AudioQueuePause(queue); 
} 

- (void)setFrequency:(NSUInteger)frequency 
{ 
    if (_frequency!=frequency) { 
     _frequency=frequency; 

     // we need to update the buffer (as soon as it stops playing) 
     rebuildBuffer=YES; 
    } 
} 

- (void)setDB:(CGFloat)dB 
{ 
    if (dB!=_dB) { 
     _dB=dB; 

     // we need to update the buffer (as soon as it stops playing) 
     rebuildBuffer=YES; 
    } 
} 

@end

的類生成在給定整頻率的餘弦波形的振盪（振幅* COS（2PI *頻率* t）的）;整個工作由void handleBuffer(...)完成，使用帶有線性PCM，單聲道，float @ 44.1kHz格式的AudioQueue。爲了改變信號形狀，你可以改變那條線。例如，下面的代碼將產生一個方波：
```
float x = fmodf(unit*(CGFloat)(tone.frequency*i), 2 * M_PI); 
data[i] = amplitude * (x > M_PI ? -1.0 : 1.0); 
```
對於浮點頻率，則應考慮不存在necessarely在音頻數據的二分之一振盪的整數倍，所以信號表示在兩個緩衝區之間的連接處是不連續的，併產生一個奇怪的「嘀嗒」。例如，您可以設置較少的採樣點，以便結點處於信號週期的末尾。
正如Paul R指出的那樣，您應該首先校準硬件，以獲得您在實施中設置的值與設備產生的聲音之間的可靠轉換。實際上，此代碼中生成的浮點採樣範圍爲-1到1，因此我只是將幅度值轉換爲dB（20 * log_10（幅度））。
查看實施中的其他詳細信息以及「已知限制」（所有這些「待辦事項」）的註釋。蘋果在其參考文獻中詳細記錄了所使用的功能。

來源

2012-11-11 02:13:52

不適用於我。安靜。或者我不明白如何使用此代碼。 –

@ValeriyVan再次測試它，它確實有效。與AudioToolbox.framework鏈接，只有一個視圖和一個調用'[tone play]「的按鈕;'。你可以說得更詳細點嗎？ –

我已經建立了乾淨的測試項目來玩這個，現在它的工作。但麥汁是那些定期點擊？我在模擬器以及真實設備上聽到他們的聲音。 –

在iphone上播放蜂鳴聲與頻率和分貝有關

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