Calibrated Acoustic Evidence: Legal and Methodological Advances in Forensic Voice Comparison for Indonesia
DOI:
https://doi.org/10.61978/lingua.v2i4.987Keywords:
Forensic Voice Comparison, Likelihood Ratio, Indonesia, Acoustic Features, Speaker Identification, Expert Testimony, Digital EvidenceAbstract
Forensic voice comparison (FVC) is gaining global recognition as a scientific method for speaker identification in legal proceedings. In Indonesia, however, the application of FVC remains underdeveloped, despite increasing reliance on digital and audio based evidence in criminal cases. This study presents a legally and methodologically robust framework for implementing FVC within the Indonesian judicial context. The research integrates Indonesian legal standards (KUHAP Articles 183–184, UU ITE) with international forensic protocols, including ISO/IEC 27037 for digital evidence handling. A combination of acoustic features MFCCs, F0, formants, and VTLN was extracted from disputed and reference voice samples. Likelihood ratios (LRs) were calculated using Gaussian Mixture Models, with score calibration via logistic regression. Results showed mean log LR values of 2.1 for genuine trials and –1.8 for impostor trials, with an ROC AUC of 0.91. Visual tools, including Tippett plots and ROC curves, were used to interpret and communicate evidence reliability. The findings confirm that calibrated, probabilistic FVC methods are feasible and legally admissible in Indonesia. However, challenges remain in handling low quality recordings, maintaining chain of custody, and bridging communication gaps between scientific experts and legal practitioners. The study recommends structured training, standardized protocols, and the use of visual aids to enhance evidentiary transparency. This framework lays the foundation for a scalable, court ready FVC system aligned with national law and global best practices. It supports interdisciplinary cooperation aimed at strengthening Indonesia’s forensic infrastructure.
References
Z. S., & Santoso, B. (2024). Comparison of Legal Regulations on E-Commerce in Southeast Asia (Indonesia—Singapore). International Journal for Multidisciplinary Research, 6(2). https://doi.org/10.36948/ijfmr.2024.v06i02.14632 DOI: https://doi.org/10.36948/ijfmr.2024.v06i02.14632
Awan, S. N., Bahr, R. H., Watts, S., Boyer, M., Budinsky, R. A., & Bensoussan, Y. (2024). Validity of Acoustic Measures Obtained Using Various Recording Methods Including Smartphones With and Without Headset Microphones. Journal of Speech Language and Hearing Research, 67(6), 1712–1730. https://doi.org/10.1044/2024_jslhr-23-00759 DOI: https://doi.org/10.1044/2024_JSLHR-23-00759
Bacci, N., Briers, N., & Steyn, M. (2021). Assessing the Effect of Facial Disguises on Forensic Facial Comparison by Morphological Analysis. Journal of Forensic Sciences, 66(4), 1220–1233. https://doi.org/10.1111/1556-4029.14722 DOI: https://doi.org/10.1111/1556-4029.14722
Bunger, A., Skordos, D., Trueswell, J. C., & Papafragou, A. (2021). How Children Attend to Events Before Speaking: Crosslinguistic Evidence From the Motion Domain. Glossa a Journal of General Linguistics, 6(1). https://doi.org/10.5334/gjgl.1210 DOI: https://doi.org/10.5334/gjgl.1210
Cheung, S., & Babel, M. (2022). The Own-Voice Benefit for Word Recognition in Early Bilinguals. Frontiers in Psychology, 13. https://doi.org/10.3389/fpsyg.2022.901326 DOI: https://doi.org/10.3389/fpsyg.2022.901326
Djafri, M. T., Asri, A., & Muhammad, I. (2024). Tinjauan Hukum Islam Terhadap Rekaman Suara Sebagai Alat Bukti Tindak Pidana Di Peradilan. Al-Qiblah Jurnal Studi Islam Dan Bahasa Arab, 3(3), 325–350. https://doi.org/10.36701/qiblah.v3i3.1451 DOI: https://doi.org/10.36701/qiblah.v3i3.1451
Ferragne, E., Talbot, A. G., Cecchini, M., Beugnet, M., Delanoë-Brun, E., Georgeton, L., Stécoli, C., Bonastre, J.-F., & Fredouille, C. (2024). Forensic Audio and Voice Analysis: TV Series Reinforce False Popular Beliefs. Languages, 9(2), 55. https://doi.org/10.3390/languages9020055 DOI: https://doi.org/10.3390/languages9020055
Garrett, B. L., Crozier, W., & Grady, R. H. (2020). Error Rates, Likelihood Ratios, and Jury Evaluation of Forensic Evidence. Journal of Forensic Sciences, 65(4), 1199–1209. https://doi.org/10.1111/1556-4029.14323 DOI: https://doi.org/10.1111/1556-4029.14323
Geng, P., Guo, H., Lu, Q., Zenng, J., & Li, Y. (2022). Is It Possible to Predict Speaker’s Body Size and Oral Cavity Characteristics From Speech Signals: A Preliminary Study on Mandarin Chinese. 34. https://doi.org/10.1117/12.2661788 DOI: https://doi.org/10.1117/12.2661788
Geoffrey, S. M., Enzinger, E., Ramos, D., González-Rodríguez, J., & Lozano-Díez, A. (2020). Statistical Models in Forensic Voice Comparison. 451–497. https://doi.org/10.1201/9780367527709-20 DOI: https://doi.org/10.1201/9780367527709-20
Gold, E., & French, P. (2019). International Practices in Forensic Speaker Comparisons. International Journal of Speech Language and the Law, 26(1), 1–20. https://doi.org/10.1558/ijsll.38028 DOI: https://doi.org/10.1558/ijsll.38028
Gully, A., Harrison, P., Hughes, V., Rhodes, R., & Wormald, J. (2022). How Voice Analysis Can Help Solve Crimes. Frontiers for Young Minds, 10. https://doi.org/10.3389/frym.2022.702664 DOI: https://doi.org/10.3389/frym.2022.702664
Hughes, V., & Wormald, J. (2020). Sharing Innovative Methods, Data and Knowledge Across Sociophonetics and Forensic Speech Science. Linguistics Vanguard, 6(s1). https://doi.org/10.1515/lingvan-2018-0062 DOI: https://doi.org/10.1515/lingvan-2018-0062
Kusnanto, K. (2021). The Concept of Audio-Visual Evidence in the Criminal Violation According to Criminal Procedural Law. https://doi.org/10.4108/eai.14-4-2021.2312445 DOI: https://doi.org/10.4108/eai.14-4-2021.2312445
Lee, Y., Keating, P., & Kreiman, J. (2019). Acoustic Voice Variation Within and Between Speakers. The Journal of the Acoustical Society of America, 146(3), 1568–1579. https://doi.org/10.1121/1.5125134 DOI: https://doi.org/10.1121/1.5125134
Liu, C., Huang, T.-Y., Wu, C., Wang, J. J., Wang, L., Chan, L., Dionigi, G., Chiang, F., Tseng, H., & Lin, Y. (2021). New Developments in Anterior Laryngeal Recording Technique During Neuromonitored Thyroid and Parathyroid Surgery. Frontiers in Endocrinology, 12. https://doi.org/10.3389/fendo.2021.763170 DOI: https://doi.org/10.3389/fendo.2021.763170
Morrison, G. S. (2018). The Impact in Forensic Voice Comparison of Lack of Calibration and of Mismatched Conditions Between the Known-Speaker Recording and the Relevant-Population Sample Recordings. Forensic Science International, 283, e1–e7. https://doi.org/10.1016/j.forsciint.2017.12.024 DOI: https://doi.org/10.1016/j.forsciint.2017.12.024
Morrison, G. S., & Enzinger, E. (2019). Introduction to Forensic Voice Comparison. 599–634. https://doi.org/10.4324/9780429056253-22 DOI: https://doi.org/10.4324/9780429056253-22
Nema, K. (2025). Understanding Media Consumption, Preferences, and Satisfaction of South and Southeast Asian Religious Online Media Consumers: The Case of Radio Veritas Asia’s Website. RSC, 23(2), 426–450. https://doi.org/10.62461/knam050325 DOI: https://doi.org/10.62461/KNAM050325
Poddar, A., Sahidullah, M., & Saha, G. (2017). Speaker Verification With Short Utterances: A Review of Challenges, Trends and Opportunities. Iet Biometrics, 7(2), 91–101. https://doi.org/10.1049/iet-bmt.2017.0065 DOI: https://doi.org/10.1049/iet-bmt.2017.0065
Schnell, B., & Garner, P. N. (2019). Neural VTLN for Speaker Adaptation in TTS. https://doi.org/10.21437/ssw.2019-6 DOI: https://doi.org/10.21437/SSW.2019-6
Segundo, E. S., Tsanas, A., & Gómez‐Vilda, P. (2017). Euclidean Distances as Measures of Speaker Similarity Including Identical Twin Pairs: A Forensic Investigation Using Source and Filter Voice Characteristics. Forensic Science International, 270, 25–38. https://doi.org/10.1016/j.forsciint.2016.11.020 DOI: https://doi.org/10.1016/j.forsciint.2016.11.020
Singh, S., Moody, L., Chan, D. L., Metz, D. C., Strosberg, J., Asmis, T. R., Bailey, D. L., Bergsland, E. K., Brendtro, K., Carroll, R., Cleary, S. P., Kim, M., Kong, G., Law, C., Lawrence, B., McEwan, A., McGregor, C., Michael, M., Pasieka, J. L., … Segelov, E. (2018). Follow-Up Recommendations for Completely Resected Gastroenteropancreatic Neuroendocrine Tumors. Jama Oncology, 4(11), 1597. https://doi.org/10.1001/jamaoncol.2018.2428 DOI: https://doi.org/10.1001/jamaoncol.2018.2428
Villavicencio‐Queijeiro, A., Loyzance, C., Castillo, Z. G., Hernández, L. J. S., Castillo-Alanís, L. A., Olvera, C. P. L., & López‐Escobedo, F. (2021). Development of an Instrument for Assessing the Quality of Forensic Evidence and Expert Testimony From Three Feature‐comparison Methods: DNA, Voice, and Fingerprint Analysis. Journal of Forensic Sciences, 67(1), 217–228. https://doi.org/10.1111/1556-4029.14898 DOI: https://doi.org/10.1111/1556-4029.14898
Wicaksono, H. E. K., Cahyani, N. D. W., & Suryani, V. (2023). Analysis of the Impact of Distortion on Sound Recordings as Anti Forensic Activities. Jipi (Jurnal Ilmiah Penelitian Dan Pembelajaran Informatika), 8(1), 140–153. https://doi.org/10.29100/jipi.v8i1.3331 DOI: https://doi.org/10.29100/jipi.v8i1.3331
