Perception and transmission of sonic QR codes

Digital music presented as 96 kHz pulse code modulation (PCM) audio is envisaged to become the future standard audio format for both industry professionals and the consumer, and has the potential to carry ultrasonic embedded metadata, which can incorporate track identification information and other alphanumeric data. This thesis proposes and evaluates a standalone metadata embedding and delivery method which requires no internet connectivity or an extensive database of pre-populated audio fingerprints. This so-called Sonic Quick Response Code (SQRC) methodology provides an accessible and conveniently implemented data transmission solution. Its widespread use is dependent on both its robustness and whether it can be perceived by humans, and this latter aspect is investigated both by the application of conventional ABX listening tests and electroencephalogram (EEG) analysis.

The contribution to the core knowledge gaps in the literature are centred around the development, transmission, decode and perception of a high-resolution audio-based metadata delivery format: The Sonic Quick Response Code (SQRC). To date, the perceptual effect of ultrasonic watermarks embedded within audible range carrier signals, has not been studied using EEG methodology. This approach has enabled the direct investigation of both temporal and alpha wave activity in the human brain after acoustic exposure to ultrasonic SQRC, and forms a major contribution to the thesis.

Identification of these knowledge gaps led to the development of the following research questions:

1. Can humans actively perceive ultra-audible frequency content within an audible carrier signal that is sampled at 96 kHz?

2. Can the ultra-audible frequency range be effectively used to embed metadata, such as a web URL or text-based data in 96 kHz sampled audio?

3. Does the human brain subconsciously respond to ultra-audible signals within the same processing pathway as that of audible audio frequencies?

In order to address these research questions, a multidisciplinary approach was employed to elucidate the perceptual effects of ultrasonic perception in humans, bringing together the fields of psychoacoustics, digital watermarking and perceptual studies (ABX listening tests and EEG methodology).

Addressing Research Question 2, this multidisciplinary approach led to the development of the ultrasonic Sonic Quick Response Code (SQRC) algorithm by utilising high-resolution 96 kHz 24-bit audio for ultrasonic metadata insertion in the frequency range above that perceived by the human auditory system (HAS). Metadata in the form of, for example, an ISRC (International Standard Recording Code), was successfully embedded without compromising the underlying integrity of the high-resolution audio files. However, SQRC decode efficacy is significantly reduced by degrading its transmission with white noise of equal power.

Electroencephalogram (EEG) analysis has shown that there is a significant level of alpha wave activity produced in response to exposure from ultrasonic SQRC, thus showing cognitive perception of ultrasonic SQRC by the human brain, in response to Research Question 1. Conversely, temporal mapping of short event related potentials (ERP) after presentation of ultrasonic audio has shown that SQRC are not processed by the auditory processing centres, and topological mapping has indicated that multiple brain regions may be involved in high frequency audio perception, which will require further work to elucidate (Research Question 3).