This would be a canonical case of copyright infringement.
17 USC 106
the owner of copyright under this title has the exclusive rights to do
and to authorize any of the following....to prepare derivative works
based upon the copyrighted work
and in the definitions
A “derivative work” is a work based upon one or more preexisting
works, such as a translation, musical arrangement, dramatization,
fictionalization, motion picture version, sound recording, art
reproduction, abridgment, condensation, or any other form in which a
work may be recast, transformed, or adapted. A work consisting of
editorial revisions, annotations, elaborations, or other modifications
which, as a whole, represent an original work of authorship, is a
In other words, when you transform a work into another work, you are creating a derivative work, even if it is hard to tell what the original work was. You can read about Bridgeport v. Dimension as an example of someone being sued for copying and modifying 2 second's worth, without permission. However, there is disagreement depending on which district you are being sued in, see VMG Salsoul v. Ciccone where the court held that 230 milliseconds of copying was a trifling amount not prohibited by law. Your description suggests that this is not de minimis use.
If there is no direct evidence of copying (such as your confession), the court will rely on "substantial similarity" to determine whether you copied someone else's work. You would really need to consult with an attorney specializing on copyright law and music, to get a professional judgment of whether your work is sufficiently similar to the original.