Core Audio Swift Equalizer adjusts all bands at once?

Question

I am having trouble setting up a kAudioUnitSubType_NBandEQ in Swift. Here is my code to initialize the EQ:

  var cd:AudioComponentDescription = AudioComponentDescription(componentType: OSType(kAudioUnitType_Effect),componentSubType: OSType(kAudioUnitSubType_NBandEQ),componentManufacturer: OSType(kAudioUnitManufacturer_Apple),componentFlags: 0,componentFlagsMask: 0)

    // Add the node to the graph
    status = AUGraphAddNode(graph, &cd, &MyAppNode)
    println(status)

     // Once the graph has been opened get an instance of the equalizer
    status = AUGraphNodeInfo(graph, self.MyAppNode, nil, &MyAppUnit)
    println(status)

    var eqFrequencies: [UInt32] = [ 32, 250, 500, 1000, 2000, 16000 ]

    status = AudioUnitSetProperty(
        self.MyAppUnit,
        AudioUnitPropertyID(kAUNBandEQProperty_NumberOfBands),
        AudioUnitScope(kAudioUnitScope_Global),
        0,
        eqFrequencies,
        UInt32(eqFrequencies.count*sizeof(UInt32))
    )
    println(status)

    status = AudioUnitInitialize(self.MyAppUnit)
    println(status)

    var ioUnitOutputElement:AudioUnitElement = 0
    var samplerOutputElement:AudioUnitElement = 0

    AUGraphConnectNodeInput(graph, sourceNode, sourceOutputBusNumber, self.MyAppNode, 0)

    AUGraphConnectNodeInput(graph, self.MyAppNode, 0, destinationNode, destinationInputBusNumber)

and then to apply changes in the frequency gains my code is as follows:

if (MyAppUnit == nil) {return}
    else{

        var bandValue0 :Float32 = tenBands.objectAtIndex(0) as! Float32
        var bandValue1 :Float32 = tenBands.objectAtIndex(1) as! Float32
        var bandValue2 :Float32 = tenBands.objectAtIndex(2) as! Float32
        var bandValue3 :Float32 = tenBands.objectAtIndex(3) as! Float32
        var bandValue4 :Float32 = tenBands.objectAtIndex(4) as! Float32
        var bandValue5 :Float32 = tenBands.objectAtIndex(5) as! Float32

        AudioUnitSetParameter(self.MyAppUnit, 0, AudioUnitScope(kAudioUnitScope_Global), 0, bandValue0, 0);
        AudioUnitSetParameter(self.MyAppUnit, 1, AudioUnitScope(kAudioUnitScope_Global), 0, bandValue1, 0);
        AudioUnitSetParameter(self.MyAppUnit, 2, AudioUnitScope(kAudioUnitScope_Global), 0, bandValue2, 0);
        AudioUnitSetParameter(self.MyAppUnit, 3, AudioUnitScope(kAudioUnitScope_Global), 0, bandValue3, 0);
        AudioUnitSetParameter(self.MyAppUnit, 4, AudioUnitScope(kAudioUnitScope_Global), 0, bandValue4, 0);
        AudioUnitSetParameter(self.MyAppUnit, 5, AudioUnitScope(kAudioUnitScope_Global), 0, bandValue5, 0);
}

Can anyone point out what I am doing wrong here? I think it is related to the second variable in AudioUnitSetParameter. I have tried AudioUnitParameterID(0), and AudioUnitParameterID(kAUNBandEQParam_Gain + 1) for this Value but those don't seem to work at all. Any help is appreciated!

score 3 · Accepted Answer · answered Apr 30 '15 at 16:33

Comment adding as answer because comments are insufficient.

The following Code is in Objective-c but it should help identify your problem.

There are a number of places this might fail. Firstly, you should check the status of the AudioUnitSetParameter, and indeed all the AudioUnit Calls as this will give you a clearer point of where you're code is failing.

I've done this successfully in Objective-C and have a test app i can make available, if you need it, which shows the complete graph setup and setting the bands and gains by moving a slider ... back to your specific question. The following works just fine for me, this might help you rule out a particular section.

You can try and obtain the current "gain", this will indicate if your bands are set up correctly.

  - (AudioUnitParameterValue)gainForBandAtPosition:(uint)bandPosition
  {
      AudioUnitParameterValue gain;
      AudioUnitParameterID parameterID = kAUNBandEQParam_Gain + bandPosition;
      OSStatus status = AudioUnitGetParameter(equalizerUnit,
                                             parameterID,
                                  kAudioUnitScope_Global,
                                                       0,
                                                 &gain);

    if (status != noErr) {
    @throw [NSException exceptionWithName:@"gettingParamGainErrorException"
                                   reason:[NSString stringWithFormat:@"OSStatus Error on getting EQ Gain! Status returned %d).", (int)status]
                                 userInfo:nil];
    }

    return gain;
  }

then setting the gain can be done in the following way;

  - (void)setGain:(AudioUnitParameterValue)gain forBandAtPosition:(uint)bandPosition
  {
      AudioUnitParameterID parameterID = kAUNBandEQParam_Gain + bandPosition;
      OSStatus status = AudioUnitSetParameter(equalizerUnit,
                                                parameterID,
                                     kAudioUnitScope_Global,
                                                          0,
                                                       gain,
                                                        0);

    if (status != noErr) {
    @throw [NSException exceptionWithName:@"settingParamGainAudioErrorException"
                                   reason:[NSString stringWithFormat:@"OSStatus Error on setting EQ gain! Status returned %d).", (int)status]
                                 userInfo:nil];
    }

  }

Finally, what value are you trying to set, the valid range (if I'm not mistaken) is -125.0 to 25.0

Thank you for your response! I took your advice and created a loop that prints the current set gain of each band in the EQ: println("Gain") for i in 0...noBands - 1 { var gain: AudioUnitParameterValue = 0 var parameterID = AudioUnitParameterID(kAUNBandEQParam_Gain + i) status = AudioUnitGetParameter(self.MyAppUnit, parameterID, AudioUnitScope(kAudioUnitScope_Global), 0, &gain) println(gain) } — Paul Lehn, Apr 30 '15 at 17:17
this works fine and displays the values that I set to each band (-24 to 24). So this is not the problem. Any other ideas? — Paul Lehn, Apr 30 '15 at 17:18
one thing to note is that when i use my original AudioUnitSetParameter() functions to set the gain and print out the band's gains they do not change at all but the overall volume continues to change. Is it possible that this is a completely different equalizer? Or that I am just increasing the overall volume? — Paul Lehn, Apr 30 '15 at 17:29
Sure, here is a link to the class I am using: http://pastebin.com/Cyt45LPB. I should note this is being implemented with the Spotify SDK. — Paul Lehn, Apr 30 '15 at 18:05
i was able to answer my question from the above code so deleted my comment ... i'll take a closer look at your code and see if i can spot anything. — MDB983, Apr 30 '15 at 18:10
I think i found it ... you need to set the bypass for each of the bands you add ... OSStatus status = AudioUnitSetParameter(equalizerUnit, kAUNBandEQParam_BypassBand+i, kAudioUnitScope_Global, 0, 0, 0); — MDB983, Apr 30 '15 at 18:30
YES! this was it! I had tried setting the bypass before but didn't set 0, instead I set it with (AudioUnitParameterValue(eqFrequencies[i])). Thanks so much for your help! — Paul Lehn, Apr 30 '15 at 18:38
You're welcome ... glad i could help, i think i struggled with that too, it's so poorly documented. — MDB983, Apr 30 '15 at 18:39

Core Audio Swift Equalizer adjusts all bands at once?

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