chords, including major 7th, major 6th, minor 7th, minor/major 7th, dominant 7th, diminished, half-diminished, and augmented chords. As well, they need to learn about chord transformations (e.g., altered chords, such as "alt dominant chords" described above), chord substitutions, and re-harmonization techniques. Some jazz guitarists use their knowledge of jazz scales and chords to provide a walking bass-style accompaniment. Jazz guitarists learn to perform these chords over the range of different chord progressions used in jazz, such as the II-V-I progression, the jazz-style blues progression, the minor jazz-style blues form, the "rhythm changes" progression, and the variety of chord progressions used in jazz ballads, and jazz standards. Guitarists may also learn to use the chord types, strumming styles, and effects pedals (e.g., chorus effect or fuzzbox) used in 1970s-era jazz-Latin, jazz-funk, and jazz-rock fusion music. Big band rhythm In jazz big bands, popular during the 1930s and 1940s, the guitarist is considered an integral part of the rhythm section (guitar, drums and bass). They usually played a regular four chords to the bar, although an amount of harmonic improvisation is possible. Freddie Green, guitarist in the Count Basie orchestra, was a noted exponent of this style. The harmonies are often minimal; for instance, the root note is often omitted on the assumption that it will be supplied by the bassist. Small group comping When jazz guitarists play chords underneath a song's melody or another musician's solo improvisations, it is called comping, short for accompanying. The accompanying style in most jazz styles differs from the way chordal instruments accompany in many popular styles of music. In many popular styles of music, such as rock and pop, the rhythm guitarist usually performs the chords in rhythmic fashion which sets out the beat or groove of a tune. In contrast, in many modern jazz styles within smaller, the guitarist plays much more sparsely, intermingling periodic chords and delicate voicings into pauses in the melody or solo, and using periods of silence. Jazz guitarists commonly use a wide variety of inversions when comping, rather than only using standard voicings. Gypsy pumping Gypsy jazz is acoustic music, usually played without a drummer. Rhythm guitar in gypsy jazz uses a special form of strumming known as "la pompe", i.e. "the pump". This form of percussive rhythm is similar to the "boom-chick" in bluegrass styles; it is what gives the music its fast swinging feeling. The strumming hand,