iOS版.使用USB麦克风录制96kHz

我正在尝试使用我的RØDEiXYUSB麦克风以96kHz的速度录制.
录音没有错误,当我启动连接麦克风的应用程序时,我看到AVAudioSession以96kHz的采样率成功运行.
但是,如果我看一下光谱,很明显除了20kHz以上的重采样噪声之外什么都没有：

为了进行比较,这是使用与USB麦克风捆绑的应用程序(RØDERec)进行相同录制的频谱：

还有什么我必须做的,以原生96kHz录制？
或者也许RØDERec应用程序通过USB通过一些专有协议与麦克风通信,我在这里运气不好？

我包含了我使用的源代码：

static AudioStreamBasicDescription AudioDescription24BitStereo96000 = (AudioStreamBasicDescription) {
    .mFormatID          = kAudioFormatLinearPCM,.mFormatFlags       = kAudioFormatFlagIsPacked | kAudioFormatFlagIsSignedInteger,.mChannelsPerFrame  = 2,.mBytesPerPacket    = 6,.mFramesPerPacket   = 1,.mBytesPerFrame     = 6,.mBitsPerChannel    = 24,.mSampleRate        = 96000.0
};

- (void)setupAudioSession
{
    AVAudioSession *session = [AVAudioSession sharedInstance];
    [session setCategory:AVAudioSessionCategoryRecord error:&error];
    [session setActive:YES error:&error];
    [session setPreferredSampleRate:96000.0f error:&error];

    //I got my 96000Hz with the USB mic plugged in!
    NSLog(@"sampleRate = %lf",session.sampleRate);
}

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

    AudioComponent inputComponent = AudioComponentFindNext(NULL,&desc);
    AudioComponentInstanceNew(inputComponent,&audioUnit);

    AudioUnitScope inputBus = 1;

    UInt32 flag = 1;
    AudioUnitSetProperty(audioUnit,kAudioOutputUnitProperty_EnableIO,kAudioUnitScope_Input,inputBus,&flag,sizeof(flag));

    audioDescription = AudioDescription24BitStereo96000;

    AudioUnitSetProperty(audioUnit,kAudioUnitProperty_StreamFormat,kAudioUnitScope_Output,&audioDescription,sizeof(audioDescription));

    AURenderCallbackStruct callbackStruct;
    callbackStruct.inputProc = recordingCallback;
    callbackStruct.inputProcRefCon = (__bridge void *)(self);
    AudioUnitSetProperty(audioUnit,kAudioOutputUnitProperty_SetInputCallback,kAudioUnitScope_Global,&callbackStruct,sizeof(callbackStruct));

    AudioOutputUnitStart(audioUnit);
}

static OSStatus recordingCallback(void *inRefCon,AudioUnitRenderActionFlags *ioActionFlags,const AudioTimeStamp *inTimeStamp,UInt32 inBusNumber,UInt32 inNumberFrames,AudioBufferList *ioData)
{
    AudioBuffer audioBuffer;
    audioBuffer.mNumberChannels = 1;
    audioBuffer.mDataByteSize = inNumberFrames * audioDescription.mBytesPerFrame;
    audioBuffer.mData = malloc( inNumberFrames * audioDescription.mBytesPerFrame );

    // Put buffer in a AudioBufferList
    AudioBufferList bufferList;
    bufferList.mNumberBuffers = 1;
    bufferList.mBuffers[0] = audioBuffer;

    AudioUnitRender(audioUnit,ioActionFlags,inTimeStamp,inBusNumber,inNumberFrames,&bufferList);

    //I then take the samples and write them to WAV file
}

解决方法

在插入麦克风的情况下检查硬件采样率音频会话属性.还要检查所有音频单元功能错误返回值.

RemoteIO可能使用较低的输入采样率,然后重新采样到96k流.