Only play audio from array once without looping

Question

I'm completely a beginner when it comes to audio programming and right now I'm playing around with AudioUnit. I'm following http://www.cocoawithlove.com/2010/10/ios-tone-generator-introduction-to.html and I've ported over the code to work with iOS7. The problem is that I only want it to play the generated sine wave once and not keep on playing the sound wave. I am not sure how to accomplish this though.

Generating audio samples:

    OSStatus RenderTone(
        void *inRefCon, 
        AudioUnitRenderActionFlags *ioActionFlags, 
        const AudioTimeStamp *inTimeStamp, 
        UInt32 inBusNumber, 
        UInt32 inNumberFrames, 
        AudioBufferList *ioData)

    {
        // Fixed amplitude is good enough for our purposes
        const double amplitude = 0.25;

        // Get the tone parameters out of the view controller
        ToneGeneratorViewController *viewController =
            (ToneGeneratorViewController *)inRefCon;
        double theta = viewController->theta;
        double theta_increment =
            2.0 * M_PI * viewController->frequency / viewController->sampleRate;

        // This is a mono tone generator so we only need the first buffer
        const int channel = 0;
        Float32 *buffer = (Float32 *)ioData->mBuffers[channel].mData;

        // Generate the samples
        for (UInt32 frame = 0; frame < inNumberFrames; frame++) 
        {
            buffer[frame] = sin(theta) * amplitude;

            theta += theta_increment;
            if (theta > 2.0 * M_PI)
            {
                theta -= 2.0 * M_PI;
            }
        }

        // Store the updated theta back in the view controller
        viewController->theta = theta;

        return noErr;
    }

Creating AudioUnit:

// Configure the search parameters to find the default playback output unit
// (called the kAudioUnitSubType_RemoteIO on iOS but
// kAudioUnitSubType_DefaultOutput on Mac OS X)
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: %ld", err);

// Set our tone rendering function on the unit
AURenderCallbackStruct input;
input.inputProc = RenderTone;
input.inputProcRefCon = self;
err = AudioUnitSetProperty(toneUnit, 
    kAudioUnitProperty_SetRenderCallback, 
    kAudioUnitScope_Input,
    0, 
    &input, 
    sizeof(input));
NSAssert1(err == noErr, @"Error setting callback: %ld", 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 = sampleRate;
streamFormat.mFormatID = kAudioFormatLinearPCM;
streamFormat.mFormatFlags =
    kAudioFormatFlagsNativeFloatPacked | kAudioFormatFlagIsNonInterleaved;
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: %ld", err);

Thanks!

sergio sergio · Accepted Answer · 2014-06-26T17:14:08

The problem is that I only want it to play the generated sine wave once

What you should do is stopping the audio unit after a certain time.

You could, e.g., set an NSTimer when you call AudioOutputUnitStart and then when the timer fires, you call AudioOutputUnitStop (actually, your audio unit disposal code). Even simpler, you could use performSelector:withObject:afterDelay: and call your audio unit disposal method.

Hope this helps.

Only play audio from array once without looping

1 Answers