There have been all sorts of law suits on this topic, particularly in the '90s. The issue is fact intensive and relates to how much did you sample from the original work, would your purchasers recognize the source of the material that you took, is your work likely to diminish the economic value of the original work. In 1994, the Supreme Court cited from the Folsom v. Marsh case:"look to the nature and objects of the selections made, the quantity and value of the materials used, and the degree in which the use may prejudice the sale, or diminish the profits, or supersede the objects, of the original work." Folsom v. Marsh, 9 F.Cas. 342, 348 (No. 4,901) (CCD Mass. 1841)"See also:
http://www.ehow.com/list_6590661_copyright-laws-sampling.html
http://en.wikipedia.org/wiki/Legal_issues_surrounding_music_sampling
http://www.bmi.com/news/entry/C_in_a_Circle_-_Playing_Fair
The end result is that sometimes it is legal to sell without consent, but it is hard to identify when, so you are better off to seek consent first or not bother sampling from the music of others.
Good luck,
Todd
Answered on Dec 13th, 2013 at 8:53 AM