AVAudioEngine sound recording changes tonality

Question

I have few AVAudioPlayerNodes for each sound user can play. Each player node is connected to its own AVAudioMixerNode to change volume. All of these mixers are connected to one AVAudioMixerNode (I named it soundsMixerNode) which is connected to the engine's mainMixerNode. User can record these sounds and then play the result record via AVAudioPlayer. The problem is that this record has a shifted tonality. Like if I used a pitch effect. And I get this result only on devices, simulators works good. Maybe the problem is in AVAudioSession categories or modes? Or maybe I have problems with AVAudioFormat or setting? I don't understand. Here's my audio graph:

PlayerNode1 – MixerNode1
                        \
...                      soundsMixerNode – self.engine.mainMixerNode
                        /
PlayerNodeN – MixerNodeN

Here's my session setup:

AVAudioSession *audioSession = [AVAudioSession sharedInstance];
[audioSession setPreferredIOBufferDuration:128.0/audioSession.sampleRate error:NULL];
[audioSession setCategory:AVAudioSessionCategoryPlayAndRecord
              withOptions:AVAudioSessionCategoryOptionDefaultToSpeaker
                    error:&error];
[audioSession setActive:YES error:&error];

Here's my recording AVAudioFile setup:

NSDictionary* recordSettings = [self.engine.outputNode inputFormatForBus:0].settings;
NSError* error = nil;
self.fileForRecording = [[AVAudioFile alloc] initForWriting:url
                                                   settings:recordSettings
                                                      error:&error];

And recording code:

AVAudioFormat* recordingFormat = [self.soundsMixerNode outputFormatForBus:0];
if (recordingFormat.sampleRate > 0) {
    typeof(self) weakSelf = self;
    [self.soundsMixerNode installTapOnBus:0
                               bufferSize:1024
                                   format:recordingFormat
                                    block:^(AVAudioPCMBuffer * _Nonnull buffer, AVAudioTime * _Nonnull when) {
                                        NSError* error;
                                       [weakSelf.fileForRecording writeFromBuffer:buffer error:&error];
                                    }];
}

score 0 · Accepted Answer · answered Aug 31 '18 at 13:46

The error was in the record format. In AVAudioFile setup I used [self.engine.outputNode inputFormatForBus:0].settings, so I took an input format from my engine outputNode. But when installing tap on bus I used [self.soundsMixerNode outputFormatForBus:0]. These two formats are not equal. They have different sample rates. So I got a pitch in a result file. I need to use one format both in record file setup and in installTapOnBus:bufferSize:format:block:. In my case I need to use outputFormat of my self.soundsMixerNode.

AVAudioEngine sound recording changes tonality

1 Answers1