The Vocal Character series were designed to be a set of vocals with particular characteristics about them. For the Kagamines, two Vocaloids with contrasting vocals for a very different result despite having the same voice provider. Since they are based on the same voice provider, both successfully harmonize with each other and therefore are often used in duets together. They also share a similar range to their predecessor Miku and can be used in together with Miku successfully.Though they are voiced by the same provider, they have different pronunciations of words. Even by retuning the voice of either Kagamine to sound like the other, results are never identical, and only veteran Vocaloid fans can tell who is actually voicing the song. The reason is owed to the fact Len has a lisp-sound in his singing results that Rin does not. Len is the first male of the Vocaloid 2 era and the first male vocaloid able to hit high pitched notes. He lacks the ability to hit the lower notes less than Kaito, since he was produced as a young boy singer. Of the two voicebanks however, Len is often considered more difficult to work with than his counterpart, Rin.A particular noted weakness of Len's voicebank is that he is limited in his capabilities of matching masculine vocal tones, owed to his voice provider being female; he cannot produce a satisfactory low masculine vocal tone.
Originally Rin/Len Kagamine were regarded as a product for experienced users. Unlike Miku, they were not easy to utilize for beginners and were criticized that some voices in the original voicebanks were not clear and had pronunciation problems of the Japanese language. Their vowel sounds are choppy and overall lacked smoothness with a number of vowel related sounds being absent.
