seventh chord in the key of C Major might play an altered dominant chord built on G. An altered dominant contains flattened or sharpened "extensions" in addition to the basic elements of the chord. As well, in jazz, chordal musicians often omit the root, as this role is given to the bass player. The fifth of the chord is often omitted as well, if it is a perfect fifth above the root (as is the case in regular major chords and minor chords). The altered extensions played by a jazz guitarist or jazz pianist on an altered dominant chord on G might include (at the discretion of the performer) a flatted ninth A (a ninth scale degree flattened by one semitone); a sharp eleventh C (an eleventh scale degree raised by one semitone) and a flattened thirteenth E (a thirteenth scale degree lowered by one semitone). If the chordal playing musician were to omit the root and fifth of the dominant seventh chord (the G and D) and keep the third (B) and flatted seventh (F), and add the altered tones just listed (A, C and E), the resulting chord would be the pitches B, C, E, F, A, which is a much different-sounding chord than the standard G7 played by a pop musician (G, B, D, F). In Classical harmony and in pop music, chord voicings often double the root to emphasize the foundation of the chord progression. Soloing techniques Melodic variation and playing by ear From the dixieland era through to the swing music era, many solo performers improvised by varying and embellishing the existing melody of a song and by playing by ear over the chord changes using well-known riffs. While this approach worked well during these musical eras, given that the chord progressions were simpler and used less modulation to unusual keys, with the development of bebop in the 1940s, the embellishment and "playing by ear" approach was no longer enough. Although swing was designed for dancing, bebop was not. Bebop used complex chord progressions, unusual altered chords and extended chords, and extensive modulations, including to remote keys that are not closely related to the tonic key (the main key or home key of a song). Whereas Dixieland and swing tunes might have one chord change every two bars with some sections with one chord change per bar, bebop tunes often had two chord changes per