How does kAudioUnitSubType_NBandEQ work? Or equalizing using DSP formulas with Novocaine?

Question

I'm trying to make a 10-band equalizer and the kAudioUnitSubType_NBandEQ audio unit seems the way to go, but Apple's documentation doesn't cover how to set/configure it.

I've already connected the nodes but it errors out when I try to connect the EQNode with the iONode (output): https://gist.github.com/2295463

How do I turn the effect into a working 10-band equalizer?

Update: A working DSP formula with Novocaine is also a solution, any ideas! Those DSP formulas are quite complicated.

Update2: I prefer a working DSP formula with Novocaine since that'd be much cleaner/smaller than programming Audio Nodes.

Update3: "The Multitype EQ unit(of subtype kAudioUnitSubType_NBandEQ) provides an equalizer that can be configured as any one of the types described in “Mutitype EQ Unit Filter Types” (page 68)." Source: http://developer.apple.com/library/ios/DOCUMENTATION/AudioUnit/Reference/AudioUnit_Framework/AudioUnit_Framework.pdf But still no example.

IMPORTANT Update (17/05): I recommend everyone to use my DSP class I released on github: https://github.com/bartolsthoorn/NVDSP It'll probably save you quite some work. It will make developing a n-band equalizer or any kind of audio filters a breeze.

Answer 1

I'm the creator of Novocaine, and I've used it to make a 200-some-odd band EQ using vDSP.

I'm considering switching over to the NBandEQ audio unit, but I have a working solution with vDSP_deq22.

vDSP_deq22 filters data one sample at a time with a 2nd order IIR filter. You can find 2nd order Butterworth coefficients on musicdsp.org, or more generally by Googling. Matlab will also calculate them for you, if you have access to a copy. I used musicdsp.org. You'd create 10 vDSP_deq22 filters, run your audio through each one, multiply that band by a specified gain, and then add up the output of all the filters in the filter bank into your output audio.

Answer 2

10-band equalizer can be configured as below

converterNode -> eqNode->converterNode->ioNode.

Please refere below sample code. here i have used iPodEQ unit. Replace the iPodEQunit formatspecification with 10-band equalizer.

AUNode outputNode;
AUNode iPodTimeNode;
AUNode converterNode;
AUNode converterNode2;

AudioUnit converterAU;
AudioUnit converterAU2;

printf("create client format ASBD\n");

// client format audio going into the converter
mClientFormat.SetCanonical(1, false); 
mClientFormat.mSampleRate = kGraphSampleRate;
mClientFormat.Print();

printf("create output format ASBD\n");
CAStreamBasicDescription localOutput;
localOutput.SetAUCanonical(2, false);
localOutput.mSampleRate = kGraphSampleRate;

// output format
mOutputFormat.SetCanonical(1, false); 
mOutputFormat.mSampleRate = kGraphSampleRate;
mOutputFormat.Print();

OSStatus result = noErr;

printf("-----------\n");
printf("new AUGraph\n");

// create a new AUGraph
result = NewAUGraph(&mGraph);
if (result) { printf("NewAUGraph result %ld %08X %4.4s\n", result,
                     (unsigned int)result, (char*)&result); return; }

// create three CAComponentDescription for the AUs we want in the graph

// output unit
CAComponentDescription output_desc(kAudioUnitType_Output,
                                   kAudioUnitSubType_GenericOutput,
                                   kAudioUnitManufacturer_Apple);

// iPodTime unit
CAComponentDescription iPodTime_desc(kAudioUnitType_FormatConverter,
                                     kAudioUnitSubType_AUiPodTimeOther,
                                     kAudioUnitManufacturer_Apple);


// AU Converter
CAComponentDescription converter_desc(kAudioUnitType_FormatConverter,
                                      kAudioUnitSubType_AUConverter,
                                      kAudioUnitManufacturer_Apple);

printf("add nodes\n");

// create a node in the graph that is an AudioUnit, using the supplied
// AudioComponentDescription to find and open that unit
result = AUGraphAddNode(mGraph, &output_desc, &outputNode);

result = AUGraphAddNode(mGraph, &iPodTime_desc, &iPodTimeNode);

result = AUGraphAddNode(mGraph, &converter_desc, &converterNode);

result = AUGraphAddNode(mGraph, &converter_desc, &converterNode2);

// connect a node's output to a node's input
// converter -> iPodTime ->converter-> output

result = AUGraphConnectNodeInput(mGraph, converterNode2, 0, iPodTimeNode, 0);

result = AUGraphConnectNodeInput(mGraph, iPodTimeNode, 0, converterNode, 0);

result = AUGraphConnectNodeInput(mGraph, converterNode, 0, outputNode, 0);



// open the graph -- AudioUnits are open but not initialized
// (no resource allocation occurs here)
result = AUGraphOpen(mGraph);


// grab audio unit instances from the nodes
result = AUGraphNodeInfo(mGraph, converterNode, NULL, &converterAU);
result = AUGraphNodeInfo(mGraph, converterNode2, NULL, &converterAU2);
result = AUGraphNodeInfo(mGraph, iPodTimeNode, NULL, &mIPodTime);
result = AUGraphNodeInfo(mGraph, outputNode, NULL, &mOutputUnit);

//Get EQ unit format
UInt32 size ;
CAStreamBasicDescription eqDesc;
AudioUnitGetProperty(mIPodTime, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &eqDesc, &size);
eqDesc.Print();


// setup render callback struct
AURenderCallbackStruct rcbs;
rcbs.inputProc = &renderInput;
rcbs.inputProcRefCon = &mUserData;

printf("set AUGraphSetNodeInputCallback\n");

// set a callback for the specified node's specified input bus (bus 1)
result = AUGraphSetNodeInputCallback(mGraph, converterNode2, 0, &rcbs);

//SetFormat
result = AudioUnitSetProperty(converterAU2, kAudioUnitProperty_StreamFormat,
                              kAudioUnitScope_Input, 0, &mClientFormat, sizeof(mClientFormat));
result = AudioUnitSetProperty(converterAU2, kAudioUnitProperty_StreamFormat,
                              kAudioUnitScope_Output, 0, &eqDesc, sizeof(eqDesc));

printf("set converter input bus %d client kAudioUnitProperty_StreamFormat\n", 0);

// set the input stream format, this is the format of the audio
// for the converter input bus (bus 1)
result = AudioUnitSetProperty(converterAU, kAudioUnitProperty_StreamFormat,
                              kAudioUnitScope_Input, 0, &localOutput, sizeof(localOutput));


// in an au graph, each nodes output stream format (including sample rate)
// needs to be set explicitly this stream format is propagated to its
// destination's input stream format

printf("set converter output kAudioUnitProperty_StreamFormat\n");

// set the output stream format of the converter
result = AudioUnitSetProperty(converterAU, kAudioUnitProperty_StreamFormat,
                              kAudioUnitScope_Output, 0, &mOutputFormat, sizeof(mOutputFormat));

result = AudioUnitSetProperty(mOutputUnit, kAudioUnitProperty_StreamFormat,
                              kAudioUnitScope_Output, 0, &mOutputFormat, sizeof(mOutputFormat));

// set the output stream format of the iPodTime unit
result = AudioUnitSetProperty(mIPodTime, kAudioUnitProperty_StreamFormat,
                              kAudioUnitScope_Output, 0, &localOutput, sizeof(localOutput));


printf("AUGraphInitialize\n");
// add a render notification, this is a callback that the graph will call every time the graph renders
// the callback will be called once before the graph’s render operation, and once after the render operation is complete