Apart from specific instrumentation, a distinguishing characteristic of bluegrass is vocal harmony featuring two, three, or four parts, often with a dissonant or modal sound in the highest voice (see modal frame), a style described as the "high, lonesome sound. " Commonly, the ordering and layering of vocal harmony is called the "stack". A standard stack has a baritone voice at the bottom, the lead in the middle (singing the main melody) and a tenor at the top; although stacks can be altered, especially where a female voice is included. Alison Krauss and Union Station provide a good example of a different harmony stack with a baritone and tenor with a high lead, an octave above the standard melody line, sung by the female vocalist. However, by employing variants to the standard trio vocal arrangement, they were simply following a pattern existing since the early days of the genre. The Stanley Brothers utilized a high baritone part on several of their trios recorded for Columbia records during their time with that label (1950–1953). Mandolin player Pee Wee Lambert sang the high baritone above Ralph Stanley's tenor, both parts above Carter's lead vocal. This trio vocal arrangement was variously used by other groups as well. In the 1960s Flatt and Scruggs often added a fifth part to the traditional quartet parts on gospel songs, the extra part being a high baritone (doubling the baritone part sung in the normal range of that voice; E. P. Tullock [aka Cousin Jake] providing the part). The use of a high lead with the tenor and baritone below it was most famously employed by the Osborne Brothers who first employed it during their time with MGM records in the latter half of the 1950s. This vocal arrangement would be the home aspect of the Osbornes' sound with Bobby's high, clear voice at the top of the vocal stack.