## 2 Basque and Spanish: A Brief Comparison  
Basque is an isolate non-Indo-European language spoken by around 900 thousand people in a small region of Western Europe around the Biscay Bay, divided between Spain and France [30; 31]. A sizeable amount of Basque words have been borrowed from Latin, later from Romance languages (Spanish and French) and in the last decades from English, but most of the vocabulary is genuine and not related to other languages. Unlike other languages (e.g., Spanish, English), which use connectors (conjunctions, prepositions, articles, etc.) to relate words with each other, Basque is an agglutinative language which combines and adds suffixes to stems, conveying information about the case, number, person, etc. Spanish uses a verb conjugation system based on person and number while Basque combines synthetic and periphrastic conjugations: synthetic forms are built around the basic lexeme by adding markers depending on the subject, object and indirect object; on the other hand, periphrastic forms are built based on a few auxiliary verbs that convey most information. In declarative sentences, the most common order in Spanish is subject-verb-object while in Basque the most common structure is subject-object-verb.  
However, phonetically and phonologically, Basque and Castilian Spanish share many features, probably due to the fact that Castilian Spanish was strongly influenced by Basque in its origins. The sound systems of both languages are quite similar, featuring the same five vowels and the same syllable-timed phonology. The sets of consonants are almost identical, with only a few additional sounds in Basque: the phonemes /ts/, /ts/ and /s/ and some other less frequent ones [32]. Furthermore, in urban settings home to the majority of the Basque Country's population, speakers (often with Basque as their second language) tend to articulate Basque phonemes in a manner akin to Spanish, resulting in a closer approximation to Spanish phonetic realizations.  
Therefore, for the development of our database (more specifically, for the acoustic-phonetic alignment on which segment selection is based), we have defined a reduced set of grapheme units (corresponding to the most prevalent sounds/phonemes) by loosely taking into account their frequencies and their most common realizations [14]. For instance, the three Basque affricates ((f, ts' and ts) were merged into a single affricate: the one existing in Spanish (f). Similarly, the Basque fricatives s' (as in _zora_) and \(\int\) (as in _kaixo_) were collapsed into the fricative s, which exist in both Basque and Spanish. On the other hand, the Spanish fricative \(\theta\) (as in _pazo_ and _cero_), not strictly present in Basque, was retained due to its common usage in proper names.  
We ended up with a reduced set of 23 phonetic units complemented by an extra unit representing silences and other non-linguistic background events (see Table 1).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**IPA** & **ASCII** & \multicolumn{2}{c}{**Examples**} \\  & **Spanish** & **Basque** \\ \hline i & i & pico & ipar \\ u & u & duro & umore \\ e & e & pero & hemen \\ o & o & toro & hori \\ a & a & valle & kale \\ m & m & madre & ama \\ n & n & numca & neska \\ \(\eta\) & N & año & arraina \\ P & P & padre & apeza \\  & & bolsa & \\ b & b & vino & begia \\ t & t & tomo & etorri \\ d & d & dedo & denda \\ \hline \hline \end{tabular}
\end{table}
Table 1: Reduced set of phonetic units for Spanish and Basque with examples. IPA units are shown as well as the simplified ASCII encoding used in this work.