Kagamine Rin & Kagamine Len were developed by Crypton Future Media using Yamaha Corporation's Vocaloid 2. Their voices were created by taking vocal samples from
voice actress Asami Shimoda at a controlled pitch and tone. They were the second release within the "
Character Vocal Series," (abbreviated "
CV Series") which included Crypton Future Media's other Vocaloids,
Hatsune Miku and
Megurine Luka. They received mixed results from producers because compared to Hatsune Miku, they were considered much harder vocals to use. Asami Shimoda noted that she often received comments from Vocaloid fans that Rin's voice echoes within their heads and makes them feel dizzy, while Len's higher ranges were not favored by those not fond of the pair entirely. Despite being released as masculine characters, during the development of
VY2, the vocals of
Ryuto or Kagamine Len were not classified as "masculine vocals" and were not considered capable of holding low masculine tones because of it. As a result, he and Ryuto were not referenced in the development of VY2.
Additional software Due to a number of complaints and issues with the original vocal, the "ACT1" package was replaced with the "ACT2" package. This package acted independently from the original package. It addressed issues regarding their ability to vocalize clearly. People who purchased the old version were able to claim the updated disc until 20 September 2008. In 2010 after
Hatsune Miku Append was released for
Hatsune Miku,
Kagamine Rin & Len Append was released for Rin & Len. Rin's appends are "Power," "Warm," and "Sweet" while Len's appends are "Power," "Cold," and "Serious." An update,
Kagamine Rin/Len V4X, was released for
Vocaloid 4 on December 24, 2015. This package contains six Japanese vocals, three for Rin and three for Len. They are updated on the old Append vocals from Vocaloid 2. Rin's vocals are "Power E.V.E.C.," "Warm" and "Sweet" while Len's are "Power E.V.E.C.", "Cold" and "Serious." Enhanced Voice Expression Control (E.V.E.C.) is a new system developed for Piapro Studio which allows delicate changes to how phonemes sound. There are two options for the E.V.E.C. vocals: "Power" and "Soft." All Rin and Len vocals can use the new Cross-Synthesis (XSY) system developed for Vocaloid 4, though are limited to only being able to do so with other vocals of their assigned characters of "Rin" or "Len". Rin and Len each received an English vocal which was released on the same day as the Japanese vocal. These vocals are available separately as a download or as a bundle with Japanese vocals. ==Marketing==