It seems Apple have removed this feature since iPhone 6S. But input gain is adjustable on old iPhone model (iPhone 4/4s/5/5s/6)
We have got confirmation from Apple’s Developer Team.
Please reference this article:
https://forums.developer.apple.com/thread/21980
Quote from the article:
“No input gain control on 6s. Using isInputGainSettable will let you know if the input ports allow for the ability to set the input gain or not. Check, then do the appropriate thing for each case if you care to. Different hardware will always equal different capabilities over the lifetime of your application.”
We feel very sorry about this Apple’s lame decision….And it seems that they will never give it back.
As another developer said in the article:
“This sounds REALLY strange ! Starting from iPhone 4s till iPhone 6 this was available but on iPhone 6s this feature is gone ? Why is it so ????”
In the latest version of Recorder Plus, we add gain effect to adjust gain when the users stopped the recording.
First select the part you want to adjust gain, then tap “Effect”->”Gain” to preview the gain effect.