Audio beacons can synchronize and/or relay data to devices through a variety of broadcast media. This data-over-audio method uses sound waves in a similar way to how Bluetooth employs electromagnetic waves.
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README.md

XT Audio Beacons

This is a protocol for relaying data through high frequency, inaudible sound waves, essentially converting any speaker into an “Audio-Beacon.” This communications protocol utilizes sound waves in a similar way to how Bluetooth employs electromagnetic waves, offering an alternative method for transmitting data for both iOS and Android.

Advantages include:
  • No reliance on a data connection, including Wi-Fi, Bluetooth, or cellular service.
  • Ability to imperceptibly transmit data through online videos, television broadcasts, or any other sound-based media.
  • Enhancing the second-screen experience by allowing mobile devices to be informed of not only of what you are watching, but exactly how far along you are in the program. This also allows second-screens to respond to live events, such as touchdowns or breaking news.
  • Enabling proximity-awareness in slow zones and dead spots using existing speaker infrastructure.
  • Ability to synchronize devices to the nearest eighth of a second.

Who’s using XT Audio Beacons?

XT Audio Beacons have been enjoyed by over 1,000,000 users across three continents. Some of our clients include the following:

Purdue University Maquette University University of Michigan University of Alabama

University of Notre Dame University of Wisconsin Clemson University University of Nebraska

University of North Carolina Oklahoma City Thunder Atlanta Hawks Florida Panthers

Possible uses

  • Triggering commands on the smartphone through a television broadcast, online video, radio commercial, film and movies. Users can be rewarded for tuning in; products can be linked to during a featured commercial; coupons can be distributed, etc.

  • Turn $10 household speakers into iBeacons. Any speaker emitting a unique fingerprint at regular intervals can be used to detect proximity and trigger events to achieve the same effect as traditional Bluetooth beacons.

  • Location-based “push” notifications. Users can be segmented by proximity to various speakers.

  • Smartphones in the same room or across the globe can be synchronized and given precisely timed commands in real-time, or minutes, hours, or even days after the trigger was detected.

Synchronization
Villanova @ Purdue | Iowa @ Purdue | Villanova @ Marquette

  • Commands without a data connection. Because the software is triggered by sound, it can perform even where there is no data connection, Wi-Fi, or Bluetooth.

  • Authorization/ticketing — triggers can be used to verify check-in at an event, or to unlock content on your app.

  • Indoor location sensing — provide location services more accurate than GPS by making use of the existing speaker infrastructure.

  • Wherever your imagination takes you.

Demo

If the provided demo app is in open on your device, playing the following links from your desktop will trigger various events.

Integration

How it works

Any speaker can become an XT Audio Beacon. XT Audio Beacons are powered by ultrasonic fingerprints, each of which is composed of a permutation of inaudible tones lasting between 0.0005 and 0.002 seconds. The duration of the fingerprint is variable and depends on the amount of data relayed — typically a complete trigger lasts anywhere from 0.30 to 2.0 seconds.

Data is extracted from a set of 2048 frequency/amplitude vectors derived from incoming audio using a Fast Fourier Transformation (FFT). Over the course of a second, thousands of bits of data can be relayed. Our triggers are concentrated between 16-22 kHz to minimize conflict with environmental noise and to remain human-inaudible. This means that any audio containing our triggers must be in a format that supports high-pitch frequencies (e.g., WAV) and should not be converted or compressed into a lesser format (e.g., MP3).

Ultrasonic fingerprints can be generated to the point where single-use/throwaway triggers can be utilized for authorization and validation purposes, such as check-ins, private keys, and even payment processing.

To receive WAV files beyond those included in the starter pack, please email info@qraider.com. Unique WAV files for check-in and authorization purposes can also generated upon request. Please allow up to 24 hours for a response.
Note: before publishing an app containing the XT Ultrasonic Fingerprint framework, please make sure you’ve read the FAQ and terms & conditions located here.

iOS

(1) Add #import <XT/XT.h> to your header file and make your UIViewController a subclass of XTUltrasonicsViewController.

(2) Set the XTdelegate of the XTUltrasonicsViewController, typically self.

(3) Implement the method

- (void) didHearTriggerWithTitle:(NSString *)title andAmplitude:(float) mag

The amplitude measure can be used as a rough indicator of proximity to the outputting speaker.

(4) To get a list of trigger titles, call the method [self logTriggerTitles] on the XTUltrasonicsViewController subclass.

An unlimited number of triggers and trigger titles can be generated, even to the point of creating “throwaway” triggers for authorization and check-in purposes. If more triggers are needed than the default number listed by calling logTriggerTitles, simply contact info@qraider.com for customization.

(5) (optional) To control the UILabel and UIActivityIndicator at the bottom of the screen, use the methods

  • - (BOOL) changeListeningLabelText: (NSString *) text
  • - (BOOL) changeListeningLabelTextColor: (UIColor *) color
  • - (BOOL) changeListeningActivityIndicatorColor: (UIColor *) color
  • - (void) displayListeningLabel: (BOOL) display WithFadeTime: (float) t

To stop the label and activity indicator from appearing when the view loads, overwrite the method - (void) microphonePermissionGranted and do not call [super microphonePermissionGranted].

Android

(1) Add the xt.aar file to libs in your app directory. See here

(2) Add flatDir { dirs 'libs' } to repositories in your top-level build gradle. See here

(3) Subclass XTUltrasonicsActivity and implement the method public void didHearTriggerWithTitle(String title) andAmplitude:(float) mag. The amplitude measure can be used as a rough indicator of proximity to the outputting speaker.

(4) To get a list of trigger titles, call the method logTriggerTitles() on the XTUltrasonicsActivity subclass.

An unlimited number of triggers and trigger titles can be generated, even to the point of creating “throwaway” triggers for authorization and check-in purposes. If more triggers are needed than the default number listed by calling logTriggerTitles(), simply contact info@qraider.com for customization.

(5) Request microphone permission. This can be handled automatically for you by setting handleRecordPermissionsForMe = true in OnCreate. To handle recording permission yourself, set handleRecordPermissionsForMe = false in OnCreate.

To change the text presented during the microphone permission request process, simply set the following (public static) strings in OnCreate:

  • kPrePermissionTitle (Title for dialog that precedes permission request).
  • kPrePermissionBody (Body for dialog that precedes permission request).
  • kPermissionBodyRejected (Prompt that leads to app settings if mic permission is denied).
  • kMicPermissionDenyTitle (If mic permission is denied, the subsequent time the app is opened a dialog is displayed with this title).
  • kMicPermissionDenyBody (If mic permission is denied, the subsequent time the app is opened a dialog is displayed with this body).

Add to your manifest file:

  • <uses-permission android:name="android.permission.INTERNET" />
  • <uses-permission android:name="android.permission.RECORD_AUDIO" />

(6) (optional) To control the TextView at the bottom of the screen, use the methods

  • protected boolean changeListeningLabelText(String text)
  • protected boolean changeListeningLabelTextColor(int c)
  • protected void displayListeningLabelWithFadeTime(boolean display, int t)

To stop the TextView from appearing when the view loads, overwrite the method public void microphonePermissionGranted() and do not call super.microphonePermissionGranted().