"Get a license or do not sample." This terse statement from the 6th U.S. Circuit Court of Appeals opinion in Bridgeport Music Inc. v. Dimension Films
That being said, if you do not plan on attempting to mass produce the track and or broadcast it on say youtube with the intent to gain massive attention, you're not going to be prosecuted. But if you are actually good enough to potentially run into this reality, its best you locate a local music rep and begin the process of re-recording said parts (esp. vocals) and/or sorting out the contractual agreements for re-sampling - that is, if the proprietary owner of said chord/vocal/riff allows for such negotiations.
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