Changing pitch of sound in realtime

d_jones · April 2013

I have an engine sound that I want to loop and also adjust the pitch of dynamically.

Any idea how I would go about doing something like this? I see the ability to pan and change volume of a AEAudioFilePlayer object, but not pitch.

Any pointers would be appreciated!
Thanks.

Michael · April 2013

You'll probably want to use one of the audio units, like kAudioUnitSubType_NewTimePitch, etc. If you need pre-iOS 6 compatibility, you might wanna take a look at Dirac.

d_jones · April 2013

Thanks for your help Michael. I've got it working now.

kAudioUnitSubType_NewTimePitch seems to stretch the time of the sound but keep the pitch the same. kAudioUnitSubType_Varispeed actually does what I needed better.

Here's the code I used to double the pitch.

NSError *error = NULL;
AEAudioUnitFilter *pitch
= [[AEAudioUnitFilter alloc]
    initWithComponentDescription:AEAudioComponentDescriptionMake(kAudioUnitManufacturer_Apple,
                                                                 kAudioUnitType_FormatConverter,
                                                                 kAudioUnitSubType_Varispeed)
    audioController:_audioController
    error:&error];

AudioUnitSetParameter(pitch.audioUnit, kAudioUnitScope_Global, 0, kVarispeedParam_PlaybackRate, 1.25, 0);

[_audioController addFilter:pitch toChannel:track1];

Michael · April 2013

Great!

Dmitry · January 2014

Great!, but..

Is it possible to change the sound pitch without changing the speed?

nexus · March 2014

Dmitry,

kNewTimePitchParam_Pitch

should do the trick for you.

anatol_mano · May 2014

But it changes the speed and pitch (faster) every time I record.

 [_audioController addInputReceiver:_recorder];
    
    //Add Filter: Changing the pitch
    AEAudioUnitFilter *pitchFilter = [[AEAudioUnitFilter alloc]initWithComponentDescription:AEAudioComponentDescriptionMake(kAudioUnitManufacturer_Apple, kAudioUnitType_FormatConverter,
 kAudioUnitSubType_Varispeed) audioController:_audioController error:&error];
    AudioUnitSetParameter(pitchFilter.audioUnit,
 kAudioUnitScope_Global, 0, 
kVarispeedParam_PlaybackRate, 1.25, 0);
    [_audioController addFilter:pitchFilter];

Can it keep the speed at original recorded tempo while only altering (higher or lower) the pitch?
?

anatol_mano · May 2014

Solved

ricky641b · August 2014

@anatol can you please tell us how did you solved it ? It would really help us

leothiessen · December 2014

@ricky641b - even though it's a bit late, I'll post this for people searching for the answer - I implemented the NewTimePitch approach in TheGameSample Xcode project here: https://github.com/jcypher/TheAmazingAudioEngine/blob/master/TheGameSample/GameScene.swift - code snippet (in Swift) is:

// This function shows how you can change both pitch and rate independently
    func _doAddNewTimePitchFilter(snd : AEAudioFilePlayer) { // you could add 2 parameters, one for rate and one for pitch
        
        // Make an AudioUnit based filter and use the NewTimePitch audio unit to change pitch AND rate at the same time!
        if let pitchFilter = AEAudioUnitFilter(componentDescription: AEAudioComponentDescriptionMake(
            OSType(kAudioUnitManufacturer_Apple),
            OSType(kAudioUnitType_FormatConverter),
            OSType(kAudioUnitSubType_NewTimePitch)),
            audioController: _audCtrlr, error:nil) {
                
                // Random time-stretch
                var f = AudioUnitParameterValue(randomFloat()) * 0.3 // a value between 0 and 0.3
                if randomFloat() > 0.5 {
                    f *= -1.0
                }
                var status = AudioUnitSetParameter(
                    pitchFilter.audioUnit,              // inUnit : AudioUnit
                    OSType(kNewTimePitchParam_Rate),    // inID: AudioUnitParameterID
                    OSType(kAudioUnitScope_Global),     // inScope: AudioUnitScope
                    0,                                  // inElement: AudioUnitElement
                    1.0 + f,                            // inValue: AudioUnitParameterValue
                    0);                                 // inBufferOffsetInFrames: UInt32
                
                if status == noErr {
                    
                    // Random pitch
                    let i = AudioUnitParameterValue(100 + arc4random_uniform(1100)) // we could do anything from 0 to 2400
                    let randomPitch = i * AudioUnitParameterValue((randomFloat() > 0.5 ? 1 : -1))
                    status = AudioUnitSetParameter(
                        pitchFilter.audioUnit,              // inUnit : AudioUnit
                        OSType(kNewTimePitchParam_Pitch),   // inID: AudioUnitParameterID
                        OSType(kAudioUnitScope_Global),     // inScope: AudioUnitScope
                        0,                                  // inElement: AudioUnitElement
                        randomPitch,                        // inValue: AudioUnitParameterValue, +/-2400
                        0);                                 // inBufferOffsetInFrames: UInt32
                    if status == noErr {
                        _audCtrlr.addFilter(pitchFilter, toChannel: snd)
                    }
                }
        } // END if pitchFilter (NewTimePitch based)
    }

(I'm typing this on my phone, else I'd clean the code up

Changing pitch of sound in realtime

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