Silhouettes for SF-A2 miki, along with the other VOCALOIDs by AHS, were revealed on a poster on November 6, 2014. However, it was unconfirmed what they were for at the time. On November 20, it was confirmed in the VOCALOID4 debut livestream that they all, with the exception of Tohoku Zunko, would be receiving VOCALOID4 voicebanks.
On May 14, 2015, AH-Software confirmed that miki would only have a Natural voicebank and would release on June 18, 2015. It was possible to buy her Natural voicebank, but there was also information about a starter pack. Other details such as tempo, range, the prices for her packages were also revealed. It was shown that miki V4 received an official MMD model by KIO.
On June 4, a trial version for miki V4 was made available.
As her original package, the performance while singing is soft in lower notes and progressively gets powerful and sharp in higher. While the transition of both singing styles was unstable in the original library, it was improved to make it more natural and smoother.
Improved and more accurate pronunciation and better audio quality.
Most of the glitches from the V2 vocal were fixed, making the new voicebank more user friendly.
She becomes softer in higher notes and has less tension than her V2, which doesn't allow her to work well as her V2 in more fast-paced music.
In contrast, her stationaries became stable enough to maintain a good performance in slower and mellow genres.
Phonetic notes as noted:
As her V2, she will still skip the "-" phoneme.
Software issues as noted:
The new voice uses the same recordings Miki Furukawa did for SF-A2 miki V2, so aside from the quality and triphonetic data included, there are no really important or noticeable changes.
Compared to the original, this vocal sounds more sharp and isn't always smooth as a result.
miki V4 has the same problem as her V2, she will often sounds off-key, though this issue is now easier to fix with minor editing.
SF-A2 MIKI V4
Cross-Synthesis as noted:
She will register for use of XSY though naturally does not have an accompanying vocal for XSY as this is a single voicebank release.Therefore users will have to purchase addition voicebanks not belonging to SF-A2 miki at all for use of XSY from her XSY group "AHS".
From Ver.4.3.0 of the VOCALOID engine onwards, a XSY group "AHS" was added to VOCALOID. All vocals within the "AHS" group can XSY with each other. This vocal release is part of this group. If a user owns one or more vocal releases within the "AHS" group, XSY between them will open up.
The "AHS" group is currently the second largest XSY group within VOCALOID, having a total of 14 voicebanks that can XSY with each other. If old versions that have since been re-released are removed, there are currently 12 unique voicebanks. These are: "Yuzuki Yukari Jun", "Yuzuki Yukari Onn", "Yuzuki Yukari Lin", "SF-A2 miki", "Tohoku Zunko", "Macne Nana", "Macne Petit", "Kizuna Akari", "Hiyama Kiyoteru Natural", "Hiyama Kiyoteru Rock", "Nekomura Iroha Natural" and "Nekomura Iroha Soft".
In total if a user was to own every VOCALOID3 and VOCALOID4 AH-Software vocal within the "AHS" group, this offers the equivalent of 182 additional voicebanks achievable via XSY. The total tone variation offered by the combined packages comes to a theoretical 196 voicebanks in total.
Note that also "GWL" does not become viable for use with any V3 vocals used as the primarily vocal. This should be considered when using any vocal for XSY within the "AHS" group from V3.
Also note that the updated vocals that brought a VOCALOID from VOCALOID3 into VOCALOID4 provided few differences, aside from adding GWL. Therefore these updates can provide little difference when used for XSY.