iOS AudioUnits pass through

Question

I am trying to write an iOS application that will pass the sound received from microphone to speaker without any changes. I've read apple docs and guides. I choosed the first pattern from this guide. But nothing happening - silence. As you can see I've tried to use the AUAudioGraph (commented) - same result (do I need it in this simple example at all?).

I saw few examples in the internet where callbacks are used, but I do not want use any. Is it possible?

Any suggestions? Thanks for attention.

The actual code

#import "AudioController.h"
#import <AudioToolbox/AudioToolbox.h>
#import <AVFoundation/AVFoundation.h>
#import <AudioToolbox/AudioServices.h>
#define kInputBus 1
#define kOutputBus 0

@interface AudioController ()
{
    AudioComponentDescription desc;
    AudioComponent component;
    AudioUnit unit;
    AudioStreamBasicDescription audioFormat;
    double rate;
    //AUGraph graph;
}


@end

@implementation AudioController

- (void) setUp {
    AVAudioSession *sess = [AVAudioSession sharedInstance];
    NSError *error = nil;
    rate = 44100.0;
    [sess setPreferredSampleRate:rate error:&error];
    [sess setCategory:AVAudioSessionCategoryPlayAndRecord error:&error];
    [sess setActive:YES error:&error];
    rate = [sess sampleRate];
    if (error) {
        NSLog(@"%@", error);
    }

    NSLog(@"Init...");
    [self createUnitDesc];
    [self getComponent];
    [self getAudioUnit];
    [self enableIORec];
    [self enableIOPb];
    [self createFormat];
    [self applyFormat];
    OSStatus err = AudioUnitInitialize(unit);
    if (noErr != err) {
        [self showStatus:err];
    }
    /*NewAUGraph(&graph);
    AUNode node;
    AUGraphAddNode(graph, &desc, &node);
AUGraphInitialize(graph);
AUGraphOpen(graph);*/
}

- (void) createUnitDesc {
    desc.componentType = kAudioUnitType_Output;
    desc.componentSubType = kAudioUnitSubType_RemoteIO;
    desc.componentFlags = 0;
    desc.componentFlagsMask = 0;
    desc.componentManufacturer = kAudioUnitManufacturer_Apple;

}

- (void) getComponent {
    component = AudioComponentFindNext(NULL, &desc);
}

- (void) getAudioUnit {
    OSStatus res = AudioComponentInstanceNew(component, &unit);
    if (noErr != res) {
        [self showStatus:res];
    }
}

- (void) enableIORec {
    UInt32 flag = 1;
    OSStatus err = AudioUnitSetProperty(unit,
                                  kAudioOutputUnitProperty_EnableIO,
                                  kAudioUnitScope_Input,
                                  kInputBus,
                                  &flag,
                                  sizeof(flag));
    if (noErr != err) {
        [self showStatus:err];
    }
}

- (void) enableIOPb {
    UInt32 flag = 1;
    OSStatus err = AudioUnitSetProperty(unit,
                                  kAudioOutputUnitProperty_EnableIO,
                                  kAudioUnitScope_Output,
                                  kOutputBus,
                                  &flag,
                                  sizeof(flag));
    if (noErr != err) {
        [self showStatus:err];
    }
}

- (void) createFormat {
    // Describe format
    audioFormat.mSampleRate         = rate;//44100.00;
    audioFormat.mFormatID           = kAudioFormatLinearPCM;
    audioFormat.mFormatFlags        = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
    audioFormat.mFramesPerPacket    = 1;
    audioFormat.mChannelsPerFrame   = 1;
    audioFormat.mBitsPerChannel     = 16;
    audioFormat.mBytesPerPacket     = 2;
    audioFormat.mBytesPerFrame      = 2;
}

- (void) applyFormat {
    OSStatus err = AudioUnitSetProperty(unit,
                                  kAudioUnitProperty_StreamFormat,
                                  kAudioUnitScope_Output,
                                  kInputBus,
                                  &audioFormat,
                                  sizeof(audioFormat));
    if (noErr != err) {
        [self showStatus:err];
    }
}

- (void) start {
    NSLog(@"starting");
    OSStatus err = AudioOutputUnitStart(unit);
    //AUGraphStart(graph);
    if (noErr != err) {
        [self showStatus:err];
    }
}

- (void) end {
    NSLog(@"ending");
    OSStatus err = AudioOutputUnitStop(unit);
    //AUGraphStop(graph);
    if (noErr != err) {
        [self showStatus:err];
    }
}

- (void) showStatus:(OSStatus) st{
    NSString *text = nil;
    switch (st) {
        case kAudioUnitErr_CannotDoInCurrentContext: text = @"kAudioUnitErr_CannotDoInCurrentContext"; break;
        case kAudioUnitErr_FailedInitialization: text = @"kAudioUnitErr_FailedInitialization"; break;
        case kAudioUnitErr_FileNotSpecified: text = @"kAudioUnitErr_FileNotSpecified"; break;
        case kAudioUnitErr_FormatNotSupported: text = @"kAudioUnitErr_FormatNotSupported"; break;
        case kAudioUnitErr_IllegalInstrument: text = @"kAudioUnitErr_IllegalInstrument"; break;
        case kAudioUnitErr_Initialized: text = @"kAudioUnitErr_Initialized"; break;
        case kAudioUnitErr_InstrumentTypeNotFound: text = @"kAudioUnitErr_InstrumentTypeNotFound"; break;
        case kAudioUnitErr_InvalidElement: text = @"kAudioUnitErr_InvalidElement"; break;
        case kAudioUnitErr_InvalidFile: text = @"kAudioUnitErr_InvalidFile"; break;
        case kAudioUnitErr_InvalidOfflineRender: text = @"kAudioUnitErr_InvalidOfflineRender"; break;
        case kAudioUnitErr_InvalidParameter: text = @"kAudioUnitErr_InvalidParameter"; break;
        case kAudioUnitErr_InvalidProperty: text = @"kAudioUnitErr_InvalidProperty"; break;
        case kAudioUnitErr_InvalidPropertyValue: text = @"kAudioUnitErr_InvalidPropertyValue"; break;
        case kAudioUnitErr_InvalidScope: text = @"kAudioUnitErr_InvalidScope"; break;
        case kAudioUnitErr_NoConnection: text = @"kAudioUnitErr_NoConnection"; break;
        case kAudioUnitErr_PropertyNotInUse: text = @"kAudioUnitErr_PropertyNotInUse"; break;
        case kAudioUnitErr_PropertyNotWritable: text = @"kAudioUnitErr_PropertyNotWritable"; break;
        case kAudioUnitErr_TooManyFramesToProcess: text = @"kAudioUnitErr_TooManyFramesToProcess"; break;
        case kAudioUnitErr_Unauthorized: text = @"kAudioUnitErr_Unauthorized"; break;
        case kAudioUnitErr_Uninitialized: text = @"kAudioUnitErr_Uninitialized"; break;
        case kAudioUnitErr_UnknownFileType: text = @"kAudioUnitErr_UnknownFileType"; break;
        default: text = @"unknown error";
    }
    NSLog(@"TRANSLATED_ERROR = %li = %@", st, text);
}

- (void) dealloc {
    AudioUnitUninitialize(unit);

    [super dealloc];
}

@end

Looks like you're doing everything pretty much correctly. However, I don't see where you're actually connecting the output element of the input scope to the input element of the output scope. The RemoteIO unit is special in that it handles both hardware input and output, but these aren't implicitly connected when the unit is instantiated. — warrenm, Dec 01 '12 at 21:56
hmmm, could you please give me a hint how I can achieve it? Are you talking about AUAudioGraph? or there is other way to create a connection betweeen elements? Thank you. — Max Komarychev, Dec 01 '12 at 21:59
Thanks, done with AudioUnitConnection conn; conn.destInputNumber = 0; conn.sourceAudioUnit = unit; conn.sourceOutputNumber = 1; err = AudioUnitSetProperty(unit, kAudioUnitProperty_MakeConnection, kAudioUnitScope_Input, 0, &conn, sizeof(conn)); if (noErr != err) { [self showStatus:err]; } — Max Komarychev, Dec 01 '12 at 22:15

Max Komarychev · Accepted Answer · 2013-07-14T09:34:34.313

As warrenm said setting up a connection between Remote IO elements helped. So the code placed after all initialization done:

AudioUnitConnection conn;
conn.destInputNumber = kOutputBus;
conn.sourceAudioUnit = unit;
conn.sourceOutputNumber = kInputBus;
err = AudioUnitSetProperty(unit, kAudioUnitProperty_MakeConnection, kAudioUnitScope_Input, kOutputBus, &conn, sizeof(conn));
if (noErr != err) { [self showStatus:err]; }

UPDATE To make it easy to others to use the solution I will post full code here:

The .h file

#import <Foundation/Foundation.h>

@interface AudioController : NSObject

- (void)setUp;
- (void)start;
- (void)end;
@end

The .m file

#import "AudioController.h"
#import <AudioToolbox/AudioToolbox.h>
#import <AVFoundation/AVFoundation.h>
#import <AudioToolbox/AudioServices.h>
#define kInputBus 1
#define kOutputBus 0

@interface AudioController ()
{
    AudioComponentDescription desc;
    AudioComponent component;
    AudioUnit unit;
    AudioStreamBasicDescription audioFormat;
    double rate;
}
@end

@implementation AudioController

- (void)setUp
{
    AVAudioSession *sess = [AVAudioSession sharedInstance];
    NSError *error = nil;
    rate = 44100.0;
    [sess setPreferredSampleRate:rate error:&error];
    [sess setCategory:AVAudioSessionCategoryPlayAndRecord error:&error];
    [sess setActive:YES error:&error];
    rate = [sess sampleRate];
    if (error) {
        NSLog(@"%@", error);
    }

    NSLog(@"Initing");
    [self createUnitDesc];
    [self getComponent];
    [self getAudioUnit];
    [self enableIORec];
    [self enableIOPb];
    [self createFormat];
    [self applyFormat];
    OSStatus err = AudioUnitInitialize(unit);
    if (noErr != err) {
        [self showStatus:err];
    }

    AudioUnitConnection conn;
    conn.destInputNumber = 0;
    conn.sourceAudioUnit = unit;
    conn.sourceOutputNumber = 1;
    err = AudioUnitSetProperty(unit, kAudioUnitProperty_MakeConnection, kAudioUnitScope_Input, 0, &conn, sizeof(conn));
    if (noErr != err) {
        [self showStatus:err];
    }
}

- (void)createUnitDesc
{
    desc.componentType = kAudioUnitType_Output;
    desc.componentSubType = kAudioUnitSubType_RemoteIO;
    desc.componentFlags = 0;
    desc.componentFlagsMask = 0;
    desc.componentManufacturer = kAudioUnitManufacturer_Apple;

}

- (void)getComponent
{
    component = AudioComponentFindNext(NULL, &desc);
}

- (void)getAudioUnit
{
    OSStatus res = AudioComponentInstanceNew(component, &unit);
    if (noErr != res) {
        [self showStatus:res];
    }
}

- (void)enableIORec
{
    UInt32 flag = 1;
    OSStatus err = AudioUnitSetProperty(unit,
                                  kAudioOutputUnitProperty_EnableIO,
                                  kAudioUnitScope_Input,
                                  kInputBus,
                                  &flag,
                                  sizeof(flag));
    if (noErr != err) {
        [self showStatus:err];
    }
}

- (void)enableIOPb
{
    UInt32 flag = 1;
    OSStatus err = AudioUnitSetProperty(unit,
                                  kAudioOutputUnitProperty_EnableIO,
                                  kAudioUnitScope_Output,
                                  kOutputBus,
                                  &flag,
                                  sizeof(flag));
    if (noErr != err) {
        [self showStatus:err];
    }
}

- (void)createFormat
{
    // Describe format
    audioFormat.mSampleRate         = rate;
    audioFormat.mFormatID           = kAudioFormatLinearPCM;
    audioFormat.mFormatFlags        = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
    audioFormat.mFramesPerPacket    = 1;
    audioFormat.mChannelsPerFrame   = 1;
    audioFormat.mBitsPerChannel     = 16;
    audioFormat.mBytesPerPacket     = 2;
    audioFormat.mBytesPerFrame      = 2;
}

- (void)applyFormat
{
    OSStatus err = AudioUnitSetProperty(unit,
                                  kAudioUnitProperty_StreamFormat,
                                  kAudioUnitScope_Output,
                                  kInputBus,
                                  &audioFormat,
                                  sizeof(audioFormat));
    if (noErr != err) {
        [self showStatus:err];
    }
}

- (void)start
{
    NSLog(@"starting");
    OSStatus err = AudioOutputUnitStart(unit);
    if (noErr != err) {
        [self showStatus:err];
    }
}

- (void)end
{
    NSLog(@"ending");
    OSStatus err = AudioOutputUnitStop(unit);
    if (noErr != err) {
        [self showStatus:err];
    }
}

- (void)showStatus:(OSStatus)st
{
    NSString *text = nil;
    switch (st) {
        case kAudioUnitErr_CannotDoInCurrentContext: text = @"kAudioUnitErr_CannotDoInCurrentContext"; break;
        case kAudioUnitErr_FailedInitialization: text = @"kAudioUnitErr_FailedInitialization"; break;
        case kAudioUnitErr_FileNotSpecified: text = @"kAudioUnitErr_FileNotSpecified"; break;
        case kAudioUnitErr_FormatNotSupported: text = @"kAudioUnitErr_FormatNotSupported"; break;
        case kAudioUnitErr_IllegalInstrument: text = @"kAudioUnitErr_IllegalInstrument"; break;
        case kAudioUnitErr_Initialized: text = @"kAudioUnitErr_Initialized"; break;
        case kAudioUnitErr_InstrumentTypeNotFound: text = @"kAudioUnitErr_InstrumentTypeNotFound"; break;
        case kAudioUnitErr_InvalidElement: text = @"kAudioUnitErr_InvalidElement"; break;
        case kAudioUnitErr_InvalidFile: text = @"kAudioUnitErr_InvalidFile"; break;
        case kAudioUnitErr_InvalidOfflineRender: text = @"kAudioUnitErr_InvalidOfflineRender"; break;
        case kAudioUnitErr_InvalidParameter: text = @"kAudioUnitErr_InvalidParameter"; break;
        case kAudioUnitErr_InvalidProperty: text = @"kAudioUnitErr_InvalidProperty"; break;
        case kAudioUnitErr_InvalidPropertyValue: text = @"kAudioUnitErr_InvalidPropertyValue"; break;
        case kAudioUnitErr_InvalidScope: text = @"kAudioUnitErr_InvalidScope"; break;
        case kAudioUnitErr_NoConnection: text = @"kAudioUnitErr_NoConnection"; break;
        case kAudioUnitErr_PropertyNotInUse: text = @"kAudioUnitErr_PropertyNotInUse"; break;
        case kAudioUnitErr_PropertyNotWritable: text = @"kAudioUnitErr_PropertyNotWritable"; break;
        case kAudioUnitErr_TooManyFramesToProcess: text = @"kAudioUnitErr_TooManyFramesToProcess"; break;
        case kAudioUnitErr_Unauthorized: text = @"kAudioUnitErr_Unauthorized"; break;
        case kAudioUnitErr_Uninitialized: text = @"kAudioUnitErr_Uninitialized"; break;
        case kAudioUnitErr_UnknownFileType: text = @"kAudioUnitErr_UnknownFileType"; break;
        default: text = @"unknown error";
    }
    NSLog(@"TRANSLATED_ERROR = %li = %@", st, text);
}

- (void)dealloc
{
    AudioUnitUninitialize(unit);

    [super dealloc];
}

@end

Can you please elaborate as to how you made it work? I am not able to get it to work — Srikanth, Jul 08 '13 at 19:20
@Srikanth, please look at the code I posted. First you need to create an object of `AudioController`, then call `setUp` and then control playback by calling `start` and `end` methods. — Max Komarychev, Jul 14 '13 at 09:36
@Srikanth create two buttons namely start and stop and then for start button outlet, call the start method and for stop button outlet, call the end method. Hope this helps. — madLokesh, Dec 19 '13 at 06:26
Very clear code, thanks, but I don't see here the callback record function — tatiana_c, May 15 '17 at 12:37

iOS AudioUnits pass through

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