Which of the following is NOT one of the key characteristics of the Afrobeat sound?

1. Horn arrangements
2. Polyrhythmic
3. Call and response ballads
4. Slow, soulful ballads

Slow, soulful ballads are NOT one of the key characteristics of the Afrobeat sound. The other three characteristics listed - horn arrangements, polyrhythmic grooves, and call and response vocals - are all essential elements of Afrobeat.

To determine which of the options is NOT a key characteristic of the Afrobeat sound, we need to understand what Afrobeat is known for. Afrobeat is a music genre that originated in Nigeria in the 1960s and is a blend of traditional Nigerian music, jazz, funk, and highlife.

1. Horn arrangements: Horn arrangements are indeed a key characteristic of Afrobeat. The genre commonly employs a large horn section to create rich and vibrant melodies.

2. Polyrhythmic: Polyrythm is also a fundamental characteristic of Afrobeat. Afrobeat music often features complex and layered rhythms created by multiple percussion instruments playing different patterns simultaneously.

3. Call and response ballads: Call and response is a traditional element often found in Afrobeat. It involves a lead vocalist or musician "calling" and the audience or other musicians "responding" with a musical phrase or line.

4. Slow, soulful ballads: Slow, soulful ballads are not typically associated with Afrobeat. Afrobeat is generally characterized by high-energy, up-tempo rhythms and driving beats. While Afrobeat can incorporate elements of soulful music, slow ballads are not a key characteristic of the genre.

Based on this analysis, we can conclude that option 4, "Slow, soulful ballads," is NOT one of the key characteristics of the Afrobeat sound.

The correct answer is 4. Slow, soulful ballads.