"Speed Limit 140 BPM Four: Breaking the Sound Barrier" is a 4-CD compilation album released by Moonshine Music, specifically focusing on the "Hardcore" electronic music genre.

* Genre: It explicitly states "HARDCORE YOU KNOW THE SCORE" at the top, and "THE ULTIMATE COLLECTION OF LONDON HARDCORE" at the bottom, confirming its genre as UK Hardcore, a subgenre of electronic dance music known for its fast tempos.

* Tempo: Each track listed on the back cover has its BPM (beats per minute) clearly indicated, ranging from 142 BPM to 161 BPM, reinforcing the "140 BPM+" theme from the front cover. This confirms the compilation focuses on very high-tempo electronic music.

* Artists and Tracks: It lists 12 tracks, featuring prominent artists in the hardcore scene such as Top Buzz, Bay B Kane, Origin Unknown, Omni Trio, DJ Crystl, LTJ Bukem & Tayla, and Metalheadz. Many of these tracks are seminal in the early 90s UK hardcore, jungle, and drum & bass scenes.

* Label and Release: The Moonshine Music logo is visible, indicating the record label. It also mentions "This compilation P & C 1994 Moonshine Music," confirming its release year.

* Compilation Series: As it's "Four" in the series, it's part of a larger collection of "Speed Limit 140 BPM+" albums released by Moonshine Music.

In essence, this is a definitive 4-CD collection of fast-paced, influential UK Hardcore, Jungle, and Drum & Bass tracks from 1994, curated by Moonshine Music, with each track exceeding 140 beats per minute. It serves as a snapshot of the sound and artists prominent in the London Hardcore scene during that era.