Sleep Dirt was released in 1979, but recorded at different occasions between 1974 and 1976. It's all studio material, with
drummer Chad Wackerman's first contribution to Zappa's music on 3 tracks (of drum over-dubs). 2 tracks feature Terry Bozzio on drums, and 1 features Chester Thompson (+ Ruth Underwood on percussion).
This is NOT a run-in-the-mill 70's rock/blues Zappa album. At times, it's even "jazzy".
All (3) vocal tracks are sung by Thana Harris, who does an excellent job with her wide-ranged (at times "dirty") voice, and gives Zappa's music a new never before introduced fresh flavour, as does the double bass (heard on 3 tracks) played by Patrick O'Hearn, and the acoustic piano of George Duke. The album is a bit short (around 38 minutes), but the intense material saves it. Shorter FZ albums have indeed been released, so at this price it isn't really a problem.
The 3+ minute title track, featuring a less professional recording technique than the other tracks (therefore giving the tune a certain charm), is an acoustic guitar duo by Frank Zappa (on lead) and James "Bird Legs" Youman - a unusually emotional ballad.
Most of the album brings out a side of Zappa's compositional technique that can't be heard anywhere else, so if you are a collector of his albums - GET THIS ONE TOO!
Sleep Dirt is among my top ten favorites. To give you an idea of my judgement, other favorites include "Apostrophie'", "Joe's Garage", "The Yellow Shark", and "Civilization Phaze III".