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435 Stars 45 Forks BSD 3-Clause "New" or "Revised" License 52 Commits 18 Opened issues


iOS framework for the Quiet Modem (data over sound)

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This is the iOS framework for

With this library, you can send data through sound.

Live demo:

Other platforms: * Javascript: * Android:

Why sound? Isn't that outdated?

If you are old enough, you may remember using dial-up modems to connect to the internet. In a sense, this package brings that back. While it's true that this is somewhat of a retro approach, consider the advantages of using sound.

  • Highly cross-platform. Any device with speakers and a microphone and sufficient computational power can use this medium to communicate.

  • No pairing. Unlike Bluetooth, sound can be used instantly without the need to pair devices. This reduces the friction and improves the user experience.

  • Embeddable content. Similar to a QR code, short packets of data can be encoded into streaming or recorded audio and can then be later decoded by this package.

What does it sound like?

The answer to this depends on which operating mode you choose. Quiet provides audible and near-ultrasonic modes. Audible modes sound something like a puff of air. The near-ultrasonic modes run at 17+kHz and are virtually inaudible to adults. Either mode can operate at relatively low volumes as long as there isn't too much background noise.

How fast does it go?

Quiet's provided audible mode transfers at approximately 7kbps. In cases where two devices are connected over a cable (via 3.5mm jack) it can run in cable mode, which transfers at approximately 64kbps.


CMake is required to build QuietModemKit. If you aren't sure if you have CMake installed, run

brew install cmake

It is recommended that you use Carthage to build QuietModemKit. Simply run

brew install cmake
and then add
github "Quiet/QuietModemKit"
to your Cartfile and run
carthage update


Transmitter: ```objc


int main(int argc, char * argv[]) { QMTransmitterConfig *txConf = [[QMTransmitterConfig alloc] initWithKey:@"ultrasonic-experimental"];

QMFrameTransmitter *tx = [[QMFrameTransmitter alloc] initWithConfig:txConf];

NSString *frame_str = @"Hello, World!"; NSData *frame = [frame_str dataUsingEncoding:NSUTF8StringEncoding]; [tx send:frame];


[tx close];

return 0;



static QMFrameReceiver *rx;

void (^recv_callback)(NSData*) = ^(NSData *frame){ printf("%s\n", [frame bytes]); };

void (^request_callback)(BOOL) = ^(BOOL granted){ QMReceiverConfig *rxConf = [[QMReceiverConfig alloc] initWithKey:@"ultrasonic-experimental"]; rx = [[QMFrameReceiver alloc] initWithConfig:rxConf]; [rx setReceiveCallback:recv_callback]; };

int main(int argc, char * argv[]) { [[AVAudioSession sharedInstance] requestRecordPermission:request_callback];


if (rx != nil) {
    [rx close];

return 0;


Note that we ask for the Record permission. This is required to use the receiver.


The modem can be used audibly or via ultrasonic sound.

are used to select modem configuration. For a full list of valid keys, refer to the top-level keys of quiet-profiles.json.


3-Claused BSD, plus third-party licenses (mix of MIT and BSD, see licenses/)

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