## 2 Voice Banking and Personalized Synthetic Voices  
Voice banking is an alternative to provide people with speech difficulties with a personalized synthetic voice. In order to do that, the person has to record a number of sentences. Using those sentences, a synthetic voice with similarity to the recordings will be provided. Voice banking differs from message banking in that the last one just stores the recorded sentences to be played back when needed exactly as recorded. The recorded sentences will usually include expressions in which tone and emotion are of importance, as can be saying 'I love you', reading a bed-time story or even laughing. Instead, voice banking uses the recorded sentences to obtain a synthetic voice that can be used within a TTS system or more generally by an AAC device in daily communication. There are several voice banking providers for English (see Ref. [30; 31; 32; 33; 34; 35]). In general, it is required that the person performs the recordings before the first symptoms of the disease are noticeable in the voice, because as commented in the introduction, this can condition the final quality of the synthetic voice. If this has already happened, some providers also offer the possibility to repair the synthetic voice, applying model surgery techniques [36; 37; 38]. On the other hand, the cited systems also differ in the number of sentences needed to be recorded (from a few hundred to several thousands) as well as on the operating systems, browsers or applications where the final user will be able to install it. Indeed, some AACs software providers do not allow the use of external voices, so some voice-banking providers also offer compatibility with the most popular commercial AACs software. Finally, also the cost of the provided services varies from one provider to another.  
When it is impossible or very difficult for the user to make the recordings, normally because the disease already affects his or her speech, they can choose a voice donor to make the recordings for them. The donors are usually chosen from close family members or friends. In Ref. [31], they recommend to provide two donors and offer a final synthetic voice with mixed characteristics. In Ref. [32], a voice selected by the provider is offered to the user among a set of thousands of voices, with characteristics similar to the provided recordings.  
To the best of our knowledge, the web-based voice-banking service in Ref. [28] is the only one provided for Spanish. In this portal, also Basque is offered, although the number of users is comparatively very small.  
This portal offers the possibility of obtaining a personalized synthetic voice in Spanish and Basque. It makes use of a statistical synthesis engine based on hidden Markov models (HMMs) [4]. Each user must record a total of 100 phonetically balanced sentences in the selected language [27]. These are parameterized using abocoder [9], a high-quality vocoder that extracts Mel-cepstral coefficients (MCEP) of order 39, log-\(f_{0}\) and maximum voiced frequency. These data are then used to adapt an average voice using state-of-the-art adaptation techniques [39] based on Constrained maximum likelihood linear regression plus maximum a posteriori adaptation (CMLLR+MAP). For Spanish, the average voice was obtained with the subset 'phonetic' from the Albayzin [40] database. It consists of 6800 sentences from 204 different speakers in which each one has recorded 160, 50 or 25 sentences. For Basque, the average voice was obtained using the database described in [41]. This consists of two speakers (one female and one male) with four hours or speech each. Currently, our voice bank has almost 9000 registered users.