Final answer:
The first feature-length animated film with stereophonic sound released in 1941 was Disney's 'Fantasia'. This film was noteworthy for its combination of animation and classical music, and it represented a technological advancement in the use of multi-channel sound in cinema.
Step-by-step explanation:
The first feature-length animated film released in 1941 with stereophonic sound was Disney's Fantasia. This innovative film combined animated imagery with classical music, and was an early example of a film utilizing multi-channel sound technology. Although the question seems specifically interested in the advancements of the 1941 feature, it's worth noting that stereophonic sound had been introduced in various forms prior to this date. The release of The Jazz Singer in 1927 marked the ushering in of the era of "talkies," and films like Flying Down to Rio (1933) continued to push the boundaries of film and sound technology. By the time Fantasia was released, motion pictures were well on their way to creating the immersive audiovisual experiences we are familiar with today.