YOU SAID:

Will promise to not do the deep voice

INTO JAPANESE

深い声をしない約束します

BACK INTO ENGLISH

promise not to make a deep voice

INTO JAPANESE

深い声を出さないと約束する

BACK INTO ENGLISH

I promise you I won't give you a deep voice.

INTO JAPANESE

私はあなたに深い声を与えないと約束します。

BACK INTO ENGLISH

I promise not to give you a deep voice.

INTO JAPANESE

私はあなたに深い声を与えないことを約束します。

BACK INTO ENGLISH

I promise not to give you a deep voice.