A Changeling's shapechanger feature allows them to change their voice as an action. But unlike Kenku, the actor feat, and Rogue(Assassin)'s impostor feature, "mimicry" isn't mentioned.
Are Changelings able to innately mimic voices or is some check required when trying to imitate a voice/vocal mannerisms?
If no check is required, what is the upper limit? Could they transform into a Kenku and use their actions to replicate that race's mimicry of any sound (e.g adopting the appearance of a Kenku, then changing tiny parts of their appearance as they change their voice to a dolphin or between other humanoids)
Best Answer
The Changeling's Shapechanger trait (E:RftLW, p. 18) says, in part:
Per Keith Baker's FAQ post on Changelings in Eberron: Rising from the Last War:
Basically, the timbre of your voice will be the same, but that doesn't guarantee you'll match their accent, their word choices, their verbal tics, etc.
Especially with the removal of the free advantage on Deception checks (that the version from UA: Eberron Races had), this means the Actor feat and/or the Assassin rogue's Impostor feature still help.
The Actor feat (PHB, p. 165) says, in part:
The advantage part is straightforward enough. The other benefit is more nuanced, and would ostensibly let you match those mannerisms and word choices and such.
The Assassin rogue's Impostor feature (PHB, p. 97) is similar:
This is very similar to the Actor feat's benefits, but you get it as an Assassin without spending a feat - and you are able to match their writing style too. The feature explicitly calls out "mannerisms" as something you "unerringly mimic" - so again, this complements the changeling's Shapechanger trait well, by letting you copy the things Shapechanger doesn't already grant you the ability to copy.
That said, this question is distinct from your other one:
No matter what form a changeling takes, its statistics and traits do not change. Per another part of the Changeling's Shapechanger trait:
Copying a kenku's appearance doesn't grant you their Mimicry trait. I'm not sure exactly how a kenku would sound "normally", but if you took a kenku's form, you would sound like a "normal" kenku if you spoke. I assume this isn't typically a concern in the Eberron setting, because kenku don't traditionally exist in Eberron; if you were to transplant them into the Eberron setting, you could opt to ignore or modify the kenku's racial curse that took away their voice.
As Exempt-Medic's answer says, you can't only partially transform yourself into another race - you can determine the specifics of your appearance as that race (e.g. hair color, skin color, sex, etc. where relevant). I think you would be able to try to mimic other creatures' voices, to the extent that you are able to make those sounds in your new form. Essentially, you'd be using the new body to make those sounds. For instance, you might not be able to mimic a dragon's roar with the vocal cords of a humanoid - whereas an actual kenku would be able to do so, due to their Mimicry racial trait.