Basso continuo parts, almost universal in the Baroque era (1600–1750), provided the harmonic structure of the music by supplying a bassline and a chord progression. The phrase is often shortened to continuo, and the instrumentalists playing the continuo part are called the continuo group. Forces The composition of the continuo group is often left to the discretion of the performers (or, for a large performance, the conductor), and practice varied enormously within the Baroque period. At least one instrument capable of playing chords must be included, such as a harpsichord, organ, lute, theorbo, guitar, regal, or harp. In addition, any number of instruments that play in the bass register may be included, such as cello, double bass, bass viol, or bassoon. In modern performances of chamber works, the most common combination is harpsichord and cello for instrumental works and secular vocal works, such as operas, and organ and cello for sacred music. A double bass may be added, particularly when accompanying a lower-pitched solo voice (e.g., a bass singer). In larger orchestral works, typically performers match the instrument families used in the full ensemble: including bassoon when the work includes oboes or other woodwinds, but restricting it to cello and/or double bass if only strings are involved, although occasionally individual movements of suites deviate from this at the musical director's discretion (e.g. bassoon without oboes). Harps, lutes, and other handheld instruments are more typical of early 17th-century music. Sometimes instruments are specified by the composer: in L'Orfeo (1607) Monteverdi calls for an exceptionally varied instrumentation, with multiple harpsichords and lutes with a bass violin in the pastoral scenes followed by lamenting to the accompaniment of organo di legno and chitarrone, while Charon stands watch to the sound of a regal. Contrabassoon is rare as a continuo instrument, but is often used in J. S. Bach's Johannespassion which calls for "bassono grosso". The keyboard (or other chord-playing instrument) player realizes (that is, adds in an improvised fashion) a continuo part by playing, in addition to the notated bass line, notes above it to complete chords, either determined ahead of time or improvised in performance. The figured bass notation, described below, is a guide, but performers are also expected to use their musical judgment and the other instruments or voices (notably the lead melody and any accidentals that might be present in it) as a guide. Experienced players sometimes incorporate motives found