Is kAudioFormatFlagIsFloat supported on iPhoneOS?

Question

I am writing an iPhone application that records and plays sound simultaneously using an audio I / O device as recommended by Apple .

I want to apply some sound effects (reverb, etc.) to the recorded audio before playing it. For these effects to work well, I need samples that should be floating point numbers, not integers. It seems this should be possible by creating AudioStreamBasicDescriptionwith kAudioFormatFlagIsFloat, set to mFormatFlags. This is what my code looks like:

AudioStreamBasicDescription streamDescription;

streamDescription.mSampleRate = 44100.0;
streamDescription.mFormatID = kAudioFormatLinearPCM;
streamDescription.mFormatFlags = kAudioFormatFlagIsFloat;
streamDescription.mBitsPerChannel = 32;
streamDescription.mBytesPerFrame = 4;
streamDescription.mBytesPerPacket = 4;
streamDescription.mChannelsPerFrame = 1;
streamDescription.mFramesPerPacket = 1;
streamDescription.mReserved = 0;

OSStatus status;

status = AudioUnitSetProperty(audioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &streamDescription, sizeof(streamDescription));
if (status != noErr)
  fprintf(stderr, "AudioUnitSetProperty (kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input) returned status %ld\n", status);

status = AudioUnitSetProperty(audioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 1, &streamDescription, sizeof(streamDescription));
if (status != noErr)
  fprintf(stderr, "AudioUnitSetProperty (kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output) returned status %ld\n", status);

However, when I run this (on iPhone 3GS running iPhoneOS 3.1.3), I get the following:

AudioUnitSetProperty (kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input) returned error -10868
AudioUnitSetProperty (kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output) returned error -10868

(- 10868 - value kAudioUnitErr_FormatNotSupported)

Apple, , 16- . aurioTouch , kAudioFormatFlagIsFloat.

, kAudioFormatFlagIsFloat iPhoneOS?

Answer 1

, . , AudioConverter. ( ) , Accelerate iOS. (: , )

-, AudioStreamBasicDescription . ,

AudioStreamBasicDescription aBasicDescription = {0};
aBasicDescription.mSampleRate       = self.samplerate;
aBasicDescription.mFormatID         = kAudioFormatLinearPCM;
aBasicDescription.mFormatFlags      = kAudioFormatFlagIsSignedInteger |     kAudioFormatFlagIsPacked;
aBasicDescription.mFramesPerPacket          = 1;
aBasicDescription.mChannelsPerFrame     = 1;
aBasicDescription.mBitsPerChannel       = 8 * sizeof(SInt16);
aBasicDescription.mBytesPerPacket       = sizeof(SInt16) * aBasicDescription.mFramesPerPacket;
aBasicDescription.mBytesPerFrame        = sizeof(SInt16) * aBasicDescription.mChannelsPerFrame

AudioStreamBasicDescription float.

AudioStreamBasicDescription floatDesc = {0};
floatDesc.mFormatID = kAudioFormatLinearPCM;      
floatDesc.mFormatFlags = kAudioFormatFlagIsFloat | kAudioFormatFlagIsPacked;
floatDesc.mBitsPerChannel = 8 * sizeof(float);
floatDesc.mFramesPerPacket = 1;                                          
floatDesc.mChannelsPerFrame = 1;           
floatDesc.mBytesPerPacket = sizeof(float) * floatDesc.mFramesPerPacket;                                                                            
floatDesc.mBytesPerFrame = sizeof(float) * floatDesc.mChannelsPerFrame;                                                                                   
floatDesc.mSampleRate = [controller samplerate];

.

UInt32 intSize = inNumberFrames * sizeof(SInt16);
UInt32 floatSize = inNumberFrames * sizeof(float);
float *dataBuffer = (float *)calloc(numberOfAudioFramesIn, sizeof(float));

. (ioData - AudioBufferList, int audio)

AudioConverterRef converter;
OSStatus err = noErr;
err = AudioConverterNew(&aBasicDescription, &floatDesct, &converter);
//check for error here in "real" code
err = AudioConverterConvertBuffer(converter, intSize, ioData->mBuffers[0].mData, &floatSize, dataBuffer);
//check for error here in "real" code
//do stuff to dataBuffer, which now contains floats
//convert the floats back by running the conversion the other way

Answer 2

Core Audio:

kAudioFormatFlagIsFloat
  Set for floating point, clear for integer.
  Available in iPhone OS 2.0 and later.
  Declared in CoreAudioTypes.h.

, .

Answer 3

.

, kAudioFormatFlagIsNonInterleaved mFormatFlags. kAudioFormatFlagIsFloat, .

, - AudioStreamBasicDescription:

streamDescription.mFormatFlags = kAudioFormatFlagIsFloat | 
                                 kAudioFormatFlagIsNonInterleaved;

, iOS , - .

Answer 4

I am doing something not related to AudioUnits, but I am using AudioStreamBasicDescriptionin iOS. I was able to use float patterns by specifying:

dstFormat.mFormatFlags = kAudioFormatFlagIsFloat | kAudioFormatFlagIsNonInterleaved | kAudioFormatFlagsNativeEndian | kLinearPCMFormatFlagIsPacked;

Core Audio Learning Book : A Practical Guide to Sound Programming for Mac and iOS was useful for this.