iOS equalizer by kAudioUnitSubType_NBandEQ

Question

I want to implement my equalizer on iOS device, and it seems to be achievable by kAudioUnitSubType_NBandEQ. However, after I set the gain of each band, I heard nothing changed on the sound.

I use the sample code of BandEQDemo(https://github.com/springlo/BandEQDemo)

OSStatus TOAUGraphAddNode(OSType inComponentType, OSType inComponentSubType, AUGraph inGraph, AUNode *outNode)
{
    AudioComponentDescription desc;
    desc.componentType = inComponentType;
    desc.componentSubType = inComponentSubType;
    desc.componentFlags = 0;
    desc.componentFlagsMask = 0;
    desc.componentManufacturer = kAudioUnitManufacturer_Apple;

    return AUGraphAddNode(inGraph, &desc, outNode);
}

TOAUGraphAddNode(kAudioUnitType_Effect,
                 kAudioUnitSubType_NBandEQ,
                 graph,
                 &eqNode);

AUGraphNodeInfo(graph,
                eqNode,
                NULL,
                &equalizerUnit);
// @[ @32, @64, @128, @256, @512, @1025, @2048, @4096, @8192, @16384 ]

Then after I set the gain and check again by these two functions:

- (AudioUnitParameterValue)gainForBandAtPosition:(NSUInteger)bandPosition
{
    AudioUnitParameterValue gain;
    AudioUnitParameterID parameterID = kAUNBandEQParam_Gain + bandPosition;

    TOThrowOnError(AudioUnitGetParameter(equalizerUnit,
                                         parameterID,
                                         kAudioUnitScope_Global,
                                         0,
                                         &gain));

    return gain;
}


- (void)setGain:(AudioUnitParameterValue)gain forBandAtPosition:(NSUInteger)bandPosition
{
    AudioUnitParameterID parameterID = kAUNBandEQParam_Gain + bandPosition;

    TOThrowOnError(AudioUnitSetParameter(equalizerUnit,
                                         parameterID,      
                                         kAudioUnitScope_Global,
                                         0,
                                         gain,
                                         0));
    NSLog(@"After set gain@[%d]->%f", bandPosition, [self gainForBandAtPosition:bandPosition]);
}

When I get the gain value of each band after I set it(-96dB ~ 24dB), it does correspond to the value I set. But I cannot hear any different on the sound.

Hi! I am looking for same EQ for AVPlayer. I had downloaded sample code of BandEQDemo. Now, I tried to run into iPhone 5s. It is showing sliders but can't hear any thing. Please help. — girish_pro, Aug 16 '16 at 06:43

score 2 · Answer 1 · answered Nov 27 '14 at 13:18

Hi fellow audio enthusiast!

I am also creating an app with an equaliser feature and have stumbled upon this web page:

http://www.deluge.co/?q=content/coreaudio-iphone-creating-graphic-equalizer

With a little of cross-referencing, I have found out that the code from your Git source lacks some key features. After line 142, additional parameter set up must be made. For example, setNumBands method is not utilised, neither is setBands. Also, make sure to include the bypass setting loop - it really won't work without it! Most importantly, check what pieces of code is lacking in your implementation, based on the ling above.

I am sorry I can't give you more through explanation; I have started to learn Audio Units a few days ago; but your question (as well as the BandEQ project) and the page I stumbled upon have solved some of my problems, so I am trying to help you as well.

Nevertheless, this is an official guide for Audio Units and do study it, as so will I! Good luck!

You're welcome! But for what it's worth, I couldn't implement the EQ because I couldn't connect a MPMusicPlayerController to my mixer (audio)unit. Sadly, I misunderstood what Audiosession is - I thought that it is a some kind of stream that carries all audio from an app, and planned to tap into that :-/ — Milan Đorić, Aug 13 '16 at 11:23
No, MPMusicPlayerController doesn't allow any kind of access to the audio file and therefore audio processing is not possible. Hope it will have more degree of freedom in the future. — John, Aug 15 '16 at 09:15

iOS equalizer by kAudioUnitSubType_NBandEQ

1 Answers1