Casual discussion of classic soul and R&B tends to focus on two cities: Detroit and Memphis. What's often overlooked is the soul music that came from the City of Brotherly Love, known simply as The Sound of Philadelphia, or TSOP for short. Developed by record producers Kenneth Gamble and Leon Huff, the Philly sound emerged in the '70s as a worthy counterpart to the music coming out of Motown and the South. As founders of Philadelphia International Records, Gamble and Huff produced a string of brilliant soul albums, creating a style best described as Motown with a little more grit. Gamble and Huff embraced the symphonic leanings of Motown, but shied away from the wall of sound approach, instead favoring arrangements that gave more space for individual instruments to shine - and vocalists more freedom to improvise.

Harold Melvin & The Blue Notes's 1975 LP Wake Up Everybody is a classic example of the Philly Sound. When Melvin stepped down as lead singer in 1970, a young Teddy Pendergrass (still performing as Theodore) became the focal point of The Blue Notes. It was under Pendergrass's lead that the group found their best success on the charts. On Wake Up Everybody Pendergrass alternates between the gruff inflections of the album's title track and the sublime whispering of slower numbers, most notably the chillingly soulful "You Know How To Make Me Feel So Good." His versatility combined with the all star songwriting and production teams of Philadelphia International makes Wake Up Everybody not only a stunning example of The Sound of Philadelphia, but a timeless album in its own right.

The album should also be noted for its socially conscious tone. Finding its roots in the gospel tradition of using spirituality as a metaphor for social change, the title track echoes the longing for what Gamble (in an inscription on the album's back cover) refers to as "the righteous government that we all have prayed for so long." While at times it hinges on preaching ("dope users, stop using that dope"), the overall message of "Wake Up Everybody" is one of fostering community and taking action: "The world won't get no better if we just let it be . We gotta change it for you an' me." As a testament to the country's willingness to support quality music with a meaningful message, "Wake Up Everybody" reached No. 1 on the R&B singles chart and No. 12 in the mainstream.

After listening to albums that are as sonically refined and as socially committed as Wake Up Everybody, it's hard not to wonder what on earth happened to R&B - and pop music in general. In trying to answer this question, it's helpful to take a close look at the legacy of Wake Up Everybody. No song can better characterize the decline of the soul aesthetic as "Don't Leave Me This Way," the opener to Wake Up Everybody's b-side. In it's initial incarnation, the song is an emotionally charged romp with Pendergrass throwing his entire spirit into the pleas of the chorus: "Baby my heart is full of / love and desire for you / Now come on girl and do / what you gotta do." But the lush arrangements and impassioned cries of the original were quickly given the disco treatment in a now ubiquitous remake by Thelma Houston. Record companies found mass appeal in the tepid instrumentation and exaggerated vocals of Houston's version, which went on to win a Grammy in 1977. Pendergrass himself was not exempt from the lure of the industry, as he soon abandoned the Blue Notes to become an oversexed R&B star, a career move that resulted in a succession of platinum albums in the late '70s.

But the legacy of Wake Up Everybody is not simply one of growing commercialization. Along with much of the PIR catalogue, Wake Up Everybody has been a continual source of inspiration for generations of artists in search of musical, as well as spiritual guidance. For Common and Kanye West's meditations on the trials of inner-city life, the meandering piano of "Wake Up Everybody" serves as a fitting backdrop.

As recently as December, emerging rapper Saigon mined the opening lick of "Don't Leave Me This Way" for a cut on his latest mixtape. As Saigon laments over "the way things (have) changed" in the music game, it becomes clear that music as timeless as Wake Up Everybody will continue to serve as inspiration, regardless of the direction of popular music.