1.2Related work

This section provides a plethora of articles that elaborate on similar themes and topics as this report aspires to.

Optimally Using the Bluetooth Subband Codec

In a study from Hoene & Hyder (2010) an experiment was performed on the Low Complexity Subband Codec (SBC) in order to find the most suitable configuration of parameters. Two tests were utilized to compare the sound quality between different settings, namely: Multiple Stimuli with Hidden Reference and Anchor (MUSHRA) and the objective Perceptual Evaluation of Audio Quality (PEAQ). They also used PEAQ to compare the audio codecs SBC, CELT, aptX and ULD while specifying that it is not sufficient without a proper subjective test, although it gives an indication of quality. There are many results regarding SBC configurations but in the stereo mode they came to the following conclusion: up to 106 kbps, the 16 kHz (sample rate) came out on top; up to 237 kbps, 32 kHz was the best; and at higher quality, the 44.1 kHz stereo encoding mode can be chosen. They also concluded that SBC has difficulties to code audio signals that contain pure tones and stable harmonic series such as the harpsichord and the pitch pipe. The second test, where multiple audio codecs were compared, resulted in the following: CELT version 0.6 outperformed all other codecs at the tested rate vs. delay trade-offs; and ULD was better than SBC when the bitrate alone was considered and equally good when the gross rate was taken into account.

The Effects of Auditory Latency on Experienced First-Person Shooter Players

Halbhuber et al. (2022) studied how auditory latency affects the experience of playing FirstPerson Shooter (FPS) video games. An experiment was conducted with 24 participants playing an FPS video game with different controlled levels of audio latency. Qualitative data were then acquired from the subjects through a questionnaire after the experiment. The results of the study indicate that the delay between the player’s actions and the corresponding sound effects in video games can have a significant impact on the players’ experience. Increased auditory latency was found to amplify feelings of tension and decrease positive feelings towards the game, with the most severe effects being observed in highly skilled players. The study concluded that low auditory latency is crucial for maintaining a positive gaming experience.

Overview and Evaluation of Bluetooth Low Energy: An Emerging LowPower Wireless Technology

Gomez et al. (2012) conducted an overview and evaluation of BLE. The study explains the BLE protocol stack, evaluates its performance and investigates its possible uses. When utilizing BLE there is a balance to be struck between energy usage, latency, piconet size and throughput, which are primarily affected by the parameters: connInterval and connSlaveLatency.

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Audibility of a CD-Standard A/D/A Loop Inserted into High-Resolution Audio Playback

Meyer & Moran (2007) performed an experiment to see if humans can notice any difference in audio quality between CD and Super Audio CD or DVD-A. They utilized a double-blind ABX test which means that the participants will listen to three separate samples: A, B and X. After listening to A and B the subject will be played sample X, which is either A or B again. Finally the participant has to discern and state if it was A or B that was disguised as sample X. The result of detectability was 49.82%, i.e., the same as chance. It is also mentioned that the data was sorted on age, sex, upper-frequency hearing limit and experience. They found no correlations between the results and the different groups. A conclusion is made that audio quality above a CD is not hearable and they state that the opposite has to be proven in a similar fashion if this is to be challenged.

Action-Sound Latency: Are Our Tools Fast Enough?

McPherson et al. (2016) performed an experiment in regards to latency on digital music platforms. They had a benchmark of 10 ms as a threshold for maximum acceptable latency. These experiments were performed on both wired and wireless platforms. The three wireless communication devices were: the x-OSC WiFi module, a pair of Xbee Series 2 wireless modules and the BLE device BLEMini from Red Bear Labs. Although the results showed that WiFi was the clear winner, it was still not good enough. The performance of Xbee showed 57 ms of latency and the BLEmini had a consistent latency of 139 ms.

LC3 and LC3plus: The new audio transmission standards for wireless communication

In this article Schnell et al. (2021) display the codecs LC3 and LC3plus, to evaluate how they answer the previous limitations for Bluetooth and Digital Enhanced Cordless Telecommunications, whose aim is to solve wireless communication at short distances. They conclude that these codecs meet the requirements of the present solutions when it comes to: call forwarding, music streaming, wireless gaming headphones, wireless microphones etc.

Perceived Audio Quality for Streaming Stereo Music

By conducting three MUSHRA audio tests Hines et al. (2014) strives to evaluate how well people can assess quality in lossy audio. This is of interest since many of the current streaming audio and video platforms utilize these compressed audio formats. The different treatments are headphones and several bitrates from a set of common codecs. One main takeaway is that people have a hard time discerning differences above 48 kbps when listening on lower quality headphones typically utilized by consumers.

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1.3Problem

Under this section the problem definition is presented in four parts, namely: the goal of the study; a motivation as to why this research is interesting; research questions with related hypotheses; and finally a set of practical steps to visualize how this research will be conducted.

Aim

The aim of this report is to compare the performance between different Bluetooth audio codecs and people’s attitude toward audio in an interactive scenario. Performance refers to the execution time to encode/decode audio, as well as the perceived quality of the decoded audio.

Motivation

There is a lack of research that solely compares codecs (not hardware) even though it has a great impact on how the wireless audio transfer will perform. This is why it is interesting to assess and evaluate different codecs performance in BLE.

The performance of an audio codec will affect multiple parameters, one being latency. This is interesting in certain real-time scenarios, such as musicians playing together, where the delay has to be imperceivable to uphold the expected Quality of Service (QoS).

Another critical parameter is the audio quality. In the end it is how humans will perceive the end product (the decoded samples) that matters, and not how efficient or well sounding the codec claims to be. Therefore it is complementary to investigate how different compression ratios compare in terms of perceived audio quality.

The expectations and demands on audio may differ for an interactive contra non-interactive scenario. If this distinction can be confirmed or discarded it can guide future development of BLE audio devices when targeting consumers. Either it is important to satisfy a specific group, such as gamers, or people in different contexts might have similar requests which makes it possible to satisfy a large population with one product.

In BLE there is no silver bullet to satisfy all requirements. There is always a compromise between energy consumption, throughput and latency (Giovanelli et al. 2015, Gomez et al. 2012) where each parameter correlates with one another. E.g., increasing the bitrate (improve sound quality) will have a direct affect on energy consumption and transmission latency.

Research questions

The codecs often have several bitrate options which effectively results in a multitude of combinations. This makes the comparison of codecs more complex and thus the questions and hypothesis will reflect that by stating pairs of codecs and bitrates.

RQ1: How do different pairs of codecs and bitrates compare in terms of time for execution?

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RQ2: How do compression with different pairs of codecs and bitrates compare in terms of perceived audio quality?

RQ3: How does the attitude towards audio quality in a real-time interactive scenario compare to a non-interactive scenario?

Hypothesis

H10: There is no significant difference in execution time between the selected pairs of codecs and bitrates.

H11: There is a significant difference in execution time between the selected pairs of codecs and bitrates.

H20: There is no significant difference in perceived audio quality between the selected pairs of codecs and bitrates.

H21: There is a significant difference in perceived audio quality between the selected pairs of codecs and bitrates.

H30: There is no significant difference in attitude toward audio quality in a real-time interactive scenario compared to a non-interactive scenario.

H31: There is a significant difference in attitude toward audio quality in a real-time interactive scenario compared to a non-interactive scenario.

Objectives

1.Explore and research literature (all).

2.Identify relevant audio codecs and explore how to compare them (all).

3.Prepare audio samples for the two experiments (Jacob).

4.Set up and run the quasi-experiment (Gustav).

5.Reach out to subjects (all).

6.Set up and run the MUSHRA-experiment (Mattias).

7.Prepare a questionnaire and conduct the survey (Jacob).

8.Analyze and present the results (individual).

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