Main findings
This study aimed to identify the distinctive acoustic features of healing music. Through a series of comparative analyses with several control music datasets, it was found that the SDs of roughness, mean and period entropy of MFCC3 exhibited the desired attributes as they were not impacted by genre, differed between healing pieces and regular pieces within the same genre, and were consistent across various HMDs. Furthermore, these three features and their correlations with perceived emotions were validated using independent music datasets.
Classical music is renowned for its refined and balanced melodies, as well as its harmonious rhythms. Although not specifically created for therapeutic purposes, classical music is believed to have a calming effect that promotes dopamine release18 and suppresses cortisol production.19 Unsurprisingly, classical music was the most frequently selected genre in this study (figure 2A). Classical music has long been associated with relaxation, stress reduction and emotional regulation. It has been shown to activate brain regions linked to positive emotions20 while decreasing activity in regions connected to negative emotions.21 It has also been used in therapeutic settings because of its potential to produce a calm state and promote healing. The present findings suggest that music therapists may be inclined to use classical music as a therapeutic intervention because of its broad recognition as a complex and sophisticated genre. Although classical music has been found to have therapeutic effects in numerous cases, not all classical music is guaranteed to have this effect.22 As shown in figure 2C, the classical pieces in the HMD were considered distinct from the general CMD. Statistically, 26.22% of acoustic features were significant. Other musical genres may also have similar healing properties, as nine genres were identified as healing music.
This study hypothesised that healing music possesses shared acoustic features that transcend different genres and categories. This notion aligns with prior research indicating that music is a universal language that surpasses cultural and genre boundaries,23 thus making it a potential therapeutic tool for individuals from diverse backgrounds. Apart from widely recognised music genres such as classical music, unique musical forms are passed down through history and tradition in certain cultures. These forms include pilgrimage songs in Nigeria, high-life drumming in Ghana, singing bowl music in India and five-element music in China.24 The present study adopted five-element music as the recognised healing music, considering the cultural context of the participants. Traditional Chinese music is based on the five-element theory and the laws of Yin and Yang, which correspond to the elements of wood, fire, earth, metal and water. Using different melodies and rhythms, five-element music is thought to regulate the balance between the body and mind.25 Although the therapeutic effects of these unique forms of traditional music have not yet been fully scientifically proven, they are used extensively and promoted. In addition to their shared recognition of healing effects, five-element music and regular therapeutic music differ significantly in several respects. The acoustic features identified through equivalence analysis in this study are likely to be relevant to healing effects. An equivalence test was conducted to assess the similarity between HMD and FEMD in terms of acoustic features. The lack of significant difference between the two datasets in a subset of acoustic features suggests that these features are shared or exhibit similar patterns for both types of music. This indicates that certain acoustic characteristics transcend specific music genres and are potentially representative of healing music in distinct categories. The identified acoustic features that showed equivalence between the HMD and FEMD can be considered potential markers or indicators of healing music. These features, which exhibited similar values or patterns in both datasets, likely contribute to the overall therapeutic or emotional impact of healing music. By highlighting these shared acoustic features, our study provides insight into the distinctive nature of healing music and contributes to our understanding of its underlying characteristics. It is important to note that although some acoustic features showed equivalence, others exhibited significant differences between the two datasets. This suggests that there are unique acoustic attributes specific to healing music. By identifying these distinct features, we can contribute to a more comprehensive understanding of the acoustic profile of healing music, which can inform the development of music recommendation systems and support the identification of therapeutic music. Along this line of research, incorporating a wider range of therapeutic music types into future studies may be worthwhile to validate further the identified potentially unique acoustic features related to therapeutic effects.
The results of this study show that certain acoustic features are more important than others in identifying healing music. Specifically, the SDs of the roughness, mean and period entropy of MFCC3 were identified as the potential distinctive acoustic features of healing music. Understanding the significance of these features can contribute to the development and evaluation of new music compositions. The SD of roughness pertains to the variation in the roughness of the audio signal, which is an indicator of the perceived irregularity or noise of the sound.26 The roughness of music alludes to the subjective perception of the dissonance or noise of the sound. In the fields of music theory and psychoacoustics, roughness is recognised as the extent of beating or ‘rough’ sensation produced by the interaction between two or more sound waves that are in close frequency proximity but not in perfect alignment.27 Given its ability to create different moods and emotional responses in listeners, roughness is an essential perceptual feature of music.28 For example, dissonant intervals in music with a high roughness can evoke feelings of tension or suspense, whereas consonant intervals in music with smoother sounds can evoke a sense of relaxation or resolution. MFCCs are a concise set of features used to describe the overall shape of a spectral envelope in an audio signal associated with timbre.29 MFCCs extract the spectral characteristics from signals and present them in a more condensed form. Each coefficient of the MFCC vector typically represents a different level of audio signal characteristics. The initial few coefficients of the MFCC vector, MFCC1 and MFCC2, capture the low-level characteristics of the signal, such as the energy and spectral slope. Conversely, higher order coefficients, such as MFCC4 and above, capture the fine-grained characteristics of the signal, such as the inter-relationships between resonance peaks. Therefore, MFCC3, which is the third MFCC coefficient, plays a crucial role in capturing the intermediate-level features in the signal. The potential utility of MFCC3 lies in its ability to provide information about various sound characteristics such as timbre and pitch, making it useful for audio recognition and music processing.30 Speech studies have found that MFCC3 is related to depression.31 However, the role of MFCC3 and its statistics in music require further exploration.
Limitations
Although we aimed to uncover universal healing features, cultural factors may have influenced the generalisability of our findings. Hence, it is essential to consider cultural diversity when applying these features to guide the future selection and generation of healing music and to conduct corresponding analyses and adjustments. Additionally, owing to the limited number of participants, the sample size of our questionnaire-based population was relatively small. Thus, collecting and analysing a larger scale HMD in the future may contribute to obtaining more representative results. Although we endeavoured to explore the relationship between the three identified features and perceived emotions by comparing them with an emotional music library, a gap remains between healing effects and perceived emotions. Future studies should devise methods to quantitatively measure the impact of these three parameters on healing effects with precision adjustments. Exploring the impact of these parameters on other physiological and psychological indicators may provide a more comprehensive understanding of the potentially distinctive acoustic features of healing music. Finally, incorporating qualitative analysis methods could enrich the interpretation of the results by elucidating the participants’ subjective experiences and meanings of music.
Implications
In summary, this study successfully identified the potentially unique acoustic characteristics of healing music, which could be advantageous for devising novel music therapies or assessing the efficacy of existing therapies. These identified acoustic features can serve as key indicators of music that elicit a calming and soothing response. By integrating these features into a music recommendation system, healthcare professionals can tailor personalised playlists for patients. Music recommendation systems that leverage artificial intelligence algorithms can analyse a patient’s physiological and psychological responses in real time through relevant biometric measures. This allows for continuously monitoring and adjusting music playlists to optimise therapeutic outcomes. Furthermore, the system can learn from the patient’s feedback and adapt recommendations over time, ensuring a more personalised and effective intervention. These technologies can potentially reach larger populations, including those with limited access to professional expertise, and provide cost-effective and easily accessible music therapy interventions. Moreover, these outcomes offer evidence for the use of music as a universal therapeutic modality to overcome cultural and genre barriers. The implications of these findings can be applied in diverse contexts, such as music therapy for stress reduction, mental health and chronic pain management. Future research could confirm the generalisability of these findings by employing larger and more diverse samples of participants and expanding the types of healing music tested. Additionally, further research should investigate the underlying neural mechanisms linking these acoustic features to therapeutic effects.