Blame is weighed on all participants.
Voice actors can't be just anybody. They have to be able to match and disguise their voice to meet different requirements. However, voice actors may be able to control apparent sound, BUT, they can't completely control what harmonics accompany their voices.
And I just did a little bit of something called a "Spectrum Analysis" Basically, what it shows is the amplitude of pitches, and I found that that pitches of slightly higher than 1000 Hz were significantly lower than other pitches. This was true for Lyra, the first girl in Eileen's anime sample clip, and in Iris.
Even more evidence for Lyra and Iris is that at precisely 6000-7000 Hz it's the lowest point in the decibels axis before finally stopping at around 20000 Hz. Basically, I have scientific proof that Iris is being voiced by Eileen Stevens, or so I have it implied, because I may be wrong, since this behavior is not present in a few other points in Eileen's clips.
Another finding: ~2000 Hz is a maximum for both Lyra and Iris. I believe the presence of 7000 Hz in the other anime clips of Eileen are because she acts with more maturity, while the first girl, Lyra, and Iris bring a more playful nature. And still, much more confident it's Eileen. As a control, Dawn has a more steady logarithmic decrease.