# Evaluation of Glottal Inverse Filtering Techniques on
## 6 Conclusions  
This work analysed the performance of state-of-the-art IAIF- and QCP-based glottal inverse filtering methods on the OPENGLOT Repository I extended with female vowels. The main conclusions are that QCP-based methods achieve the best global performance according to the considered error metrics in addition to presenting with more stable behaviour across sex, phonation type, F0, and vowels. These techniques present statistically significant lower error metrics than their IAIF counterparts. As a general trend, the results obtained for the female vowels are worse than those obtained for the male ones, except for H1H2. When looking at results in terms of F0, the study reveals a worsening of performance for high F0 values in several glottal error measures, such as RMS, NAQ and H1H2, with this behaviour being even more prominent in female vowels for IAIF-based approaches. Additionally, there is a general decrease in RMS and NAQ values when moving from tense to lax phonations, and IAIF-based methods obtain poorer performances for specific vowels (e.g., /i/ and /u/ for male data and /i/, /e/ and /ae/ for female data), with the QCP-based counterparts being more stable across all vowels. Moreover, the IOP-IAIF and GFM-IAIF variants outperform the original IAIF technique for most glottal error measures in male vowels. Regarding the spectral tilt error, ST-QCP achieves a lower value for male vowels than the original QCP, while the opposite occurs with female vowels. Future work will consider the inclusion of vocal tract-based errors as additional error measures for both GIF methods' performance analysis and their tuning. Moreover, other speech datasets that rely on physical modelling and/or real speech could be considered to contrast the obtained results of the considered GIF methods and other similar approaches following the designed analysis methodology. Finally, GIF results could also be analysed accurately to model the specific glottal source and vocal tract patterns in order to provide articulatory-based numerical simulations with the desired expressiveness using three-dimensional realistic geometries. **Supplementary Materials:** The results of the optimization process with the computed error measures were saved as csv files that can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13158775/s1](https://www.mdpi.com/article/10.3390/app13158775/s1)]([https://www.mdpi.com/article/10.3390/app13158775/s1](https://www.mdpi.com/article/10.3390/app13158775/s1)). **Author Contributions:** Conceptualization, M.F., J.C.S. and F.A.-P.; methodology, M.F., J.C.S. and F.A.-P.; software, M.F., L. J.-O. and J.C.S. ; validation, M.F. and L.J.-O. ; formal analysis, M.F. ; investigation, M.F., L.J.-O., J.C.S. and F.A.-P.; resources, M.F. ; data curation, M.F. ; writing--original draft preparation, M.F., L.J.-O., J.C.S. and F.A.-P.; writing--review and editing, M.F., L.J.-O., J.C.S. and F.A.-P.; visualization, M.F., L.J.-O. and J.C.S. ; supervision, M.F. ; project administration, F.A.-P.; funding acquisition, F.A.-P. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was partially funded by the Agencia Estatal de Investigacion (AEI) through the FEMVoQ project (PID2020-120441 GB-100/AEI/10.13039/501100011033. The authors also thank the Departament de Recerca i Universitats (Generalitat de Catalunya) for their support under Grant Ref. 2021 SGR 01396. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The dataset used in this study is based on the OPENGLOT Repository I [32]. The original corpus and the code its generation can be found at: [[http://research.spa.aalto.fi/projects/openglot/](http://research.spa.aalto.fi/projects/openglot/)]([http://research.spa.aalto.fi/projects/openglot/](http://research.spa.aalto.fi/projects/openglot/)) (accessed on 5 May 2023).