音頻單元中可能的輸出採樣率

Question

我正在嘗試爲遠程I/O音頻單元的輸入流設置不同的採樣率（如32kHz，24kHz等）。但是輸出始終以這些採樣率之一播放 - 無論我設置了什麼，這些採樣率都是 - 22.05kHz，33.1kHz，11.0kHz。令人奇怪的是，當我呼籲kAudioUnitScope_OutputAudioUnitGetProperty爲kAudioUnitProperty_SampleRate，它總是返回44.1

- (void)startToneUnit 
{ 
    AudioComponentDescription defaultOutputDescription; 
    defaultOutputDescription.componentType = kAudioUnitType_Output; 
    defaultOutputDescription.componentSubType = kAudioUnitSubType_RemoteIO; 
    defaultOutputDescription.componentManufacturer = kAudioUnitManufacturer_Apple; 
    defaultOutputDescription.componentFlags = 0; 
    defaultOutputDescription.componentFlagsMask = 0; 

     // Get the default playback output unit 
    AudioComponent defaultOutput = AudioComponentFindNext(NULL, &defaultOutputDescription); 
    NSAssert(defaultOutput, @"Can't find default output"); 

     // Create a new unit based on this that we'll use for output 
    OSErr err = AudioComponentInstanceNew(defaultOutput, &toneUnit); 
    NSAssert1(toneUnit, @"Error creating unit: %hd", err); 

     // Set our tone rendering function on the unit 
    AURenderCallbackStruct input; 
    input.inputProc = RenderTone; 
    input.inputProcRefCon = (__bridge void *)(self); 
    err = AudioUnitSetProperty(toneUnit, 
           kAudioUnitProperty_SetRenderCallback, 
           kAudioUnitScope_Input, 
           0, 
           &input, 
           sizeof(input)); 
    NSAssert1(err == noErr, @"Error setting callback: %hd", err); 

     // Set the format to 32 bit, single channel, floating point, linear PCM 
    const int four_bytes_per_float = 4; 
    const int eight_bits_per_byte = 8; 

    AudioStreamBasicDescription streamFormat; 
    streamFormat.mSampleRate = SAMPLE_RATE; 
    streamFormat.mFormatID = kAudioFormatLinearPCM; 
    streamFormat.mFormatFlags = 
    kAudioFormatFlagsNativeFloatPacked; 
    streamFormat.mBytesPerPacket = four_bytes_per_float; 
    streamFormat.mFramesPerPacket = 1; 
    streamFormat.mBytesPerFrame = four_bytes_per_float; 
    streamFormat.mChannelsPerFrame = 1; 
    streamFormat.mBitsPerChannel = four_bytes_per_float * eight_bits_per_byte; 
    err = AudioUnitSetProperty (toneUnit, 
           kAudioUnitProperty_StreamFormat, 
           kAudioUnitScope_Input, 
           0, 
           &streamFormat, 
           sizeof(AudioStreamBasicDescription)); 

    NSAssert1(err == noErr, @"Error setting stream format: %hd", err); 

     // Stop changing parameters on the unit 
    err = AudioUnitInitialize(toneUnit); 
    NSAssert1(err == noErr, @"Error initializing unit: %hd", err); 

     // Start playback 
    err = AudioOutputUnitStart(toneUnit); 
    NSAssert1(err == noErr, @"Error starting unit: %hd", err); 

    Float64 outSampleRate = 0.0; 
    UInt32 size = sizeof(Float64); 
    AudioUnitGetProperty (toneUnit, 
          kAudioUnitProperty_SampleRate, 
          kAudioUnitScope_Output, 
          0, 
          &outSampleRate, 
          &size); 
    NSLog(@"Output sample rate is now at %f Hz", outSampleRate); 

    } 

什麼都支持音頻單元的所有可能的輸出採樣率？蘋果文檔的任何引用上，這將是很大的幫助

感謝

Answer 1

AudioUnit秒，在一般情況下，可以在你指定的任何採樣速率運行。（或Mac OS X上的HAL）AudioUnits作爲硬件的外觀受到更多限制 - 變速時鐘發生器，可以以任意任意採樣率運行的採樣率發生器，都非常昂貴，通常不適合電話:)

不同的iOS硬件，硬件模型或硬件或修訂版本可能支持不同的採樣率。 RemoteIO只接受您請求的費率，並將板載轉換器設置爲最接近您請求的費率。你總是必須做一個AudioUnitGetProperty來看看你實際得到了什麼。如果您想以不同的速率錄製或工作，則需要使用轉換器插件。