AVFAudio manual rendering, abbreviated. The most concise implementation of manual audio buffer rendering using AVFoundation, using only an AVAudioSourceNode and nothing else. Plays white noise for one second.

ViewController.m

#import "ViewController.h"

@import AVFoundation;

@interface ViewController () {
    AVAudioEngine * engine;
    AVAudioSourceNode * whiteNoiseGenerator;
}

@end

@implementation ViewController

static Float32 (^(^(^randomize)(void))(Float32(^)(Float32)))(void) = ^{
    srand48((unsigned int)time(0));
    return ^ (Float32(^scale)(Float32)) {
        static Float32 random;
        return ^ Float32 {
            return (Float32)scale((random = drand48()));
        };
    };
};

static Float32 (^rescale)(Float32) = ^ Float32 (Float32 distributed_random) {
    Float32 range_max = 1.f, range_min = -1.f;

    return (distributed_random = (distributed_random * (range_max - range_min)) + range_min);
};

static Float32 (^whiteNoise)(void);

- (void)viewDidLoad {
    [super viewDidLoad];

    whiteNoise = randomize()(rescale);
    whiteNoiseGenerator = [[AVAudioSourceNode alloc] initWithRenderBlock:^OSStatus(BOOL * _Nonnull isSilence, const AudioTimeStamp * _Nonnull timestamp, AVAudioFrameCount frameCount, AudioBufferList * _Nonnull outputData) {
        Float32 * output_data_t = (Float32 *)outputData->mBuffers[0].mData;
        static Float32 value;
        for (AVAudioFrameCount frame = 0; frame < frameCount; frame++) {
            output_data_t[frame] = (value = whiteNoise());
        };
        return (OSStatus)noErr;
    }];
    
    engine = [[AVAudioEngine alloc] init];
    [engine attachNode:whiteNoiseGenerator];
    [engine connect:whiteNoiseGenerator to:engine.mainMixerNode format:nil];
    engine.mainMixerNode.outputVolume = 1.0;

    __autoreleasing NSError * error = nil;
    @try {
        !([engine startAndReturnError:&error] && !error) ?: sleep(1);
    } @catch (NSException *exception) {
        printf("\n%s\n", [[exception debugDescription] UTF8String]);
    } @finally {
        (![engine isRunning]) ?: [engine stop];
    }
}

@end