# Enrichment of Oesophageal Speech: Voice Conversion with Duration-Matched Synthetic Speech as Target
## 7 Conclusions and Future Work  
Due to the anatomical alteration post-laryngectomy, it is difficult for OS speakers to produce intelligible speech. Our study was an attempt to enhance OS with the aim of making it more intelligible. We performed voice conversion using a BLSTM network and a novel training data selection approach (using a target that is matched in duration with source) which eliminated the need for the source-target alignment process. The proposed system showed significant improvements in objective evaluations of intelligibility in comparison to our previous systems. Compared to the unprocessed OS utterances, the proposed system's outputs were recognised with more accuracy by three different ASR systems. In recent times, communication with digital assistants and other devices is on the rise. Therefore, an improvement in this direction is desirable for efficient communication with digital devices and dialogue systems. Additionally, for the three most intelligible OS speakers out of the four, the proposed system was preferred by listeners over unprocessed OS. While this is encouraging, more effort is needed to have similar results for the low intelligibility OS speaker. An extension of the system described in this paper is under development: a multi-speaker system with many OS speakers' utterances as source and corresponding duration-matched SS as target. This will be a generic OS enrichment system and will enable the enrichment of more OS speakers. In addition to ASR scores, STOI scores and preference tests, we are interested in investigating subjective and physiological listening effort for unprocessed OS, enriched OS and HS. This is because, while intelligibility reveals what percentage of the speech was understood correctly, it does not tell us how difficult it was to understand it. Listening effort provides useful additional information about whether enriched OS is easier to perceive and process compared to unprocessed OS. Therefore, our future studies will focus on LE in addition to intelligibility and listener preferences. Our aim for the future is to install this enrichment system as a face-to-face communication aid in a stand-alone device or a smartphone. The device will take the unprocessed OS input and play out the enriched version in real time or with negligible delay. Another possible practical application of the proposed system could be in the form of a software plugin coupled with the microphone of the devices used by an OS speaker. This would convert any microphone input (Unprocessed OS) to an enriched version of the speech in real time or with minimum delay. Any app which requires a microphone input will use this modified speech instead. In this way, the OS speaker would be able to use the benefits of the enriched speech for telephonic conversations, zoom calls, voice commands to digital assistants and other voice based apps. Generating real time outputs will require solving latency problems when generating BLSTM outputs (see [48] for example). Once we tackle the problems of making the enrichment system work in real time and embedding it into a device, our research efforts will be able to translate into real world applications. conceptualization, S.R. and X.S. ; methodology, S.R. and X.S. ; software, S.R. and X.S. ; validation, S.R., I.H. and E.N. ; formal analysis, S.R. ; investigation, S.R. ; resources, S.R., I.H. and E.N. ; data curation, S.R. ; writing--original draft preparation, S.R. ; writing--review and editing, S.R., I.H. and E.N. ; visualization, S.R. ; supervision, I.H. and E.N. ; project administration, I.H. and E.N. ; funding acquisition, I.H. and E.N. All authors have read and agreed to the published version of the manuscript. This project was supported by funding from the European Union's H2020 research and innovation programme under the MSCA GA 67532*4 (the ENRICH network: www.enrich-etn.eu (accessed on 25 June 2021)), and the Basque Government (PIBA_2018\(1\)0035 and IT355-19).