The strings of these instruments are generally placed on a resonating cavity and are plucked by the fingers or by a plectrum (in the harpsichord, by small plectra operated by the keys). The harp is perhaps the most iconic member of this family and, since the 19th-century, has become an indispensable element of orchestration because it can add a variety of effects including highlighting accents and adding depth of timbre. It is also famous for the glissando, its most typical articulation, which is a characteristic and evocative brush of colour that we can hear in the famous Waltz of the Flowers from the Nutcracker by P. I. Tchaikovsky. Thanks to the advent of electronics, the guitar is the instrument that has perhaps most benefited from technological-acoustic evolution. In fact, both amplification and the addition of effects of all types have radically changed its sound and given rise to a wide variety of timbres that range from the sweet and soft traditional colour heard in Study no. 1 by H. Villa Lobos to the hardness and harshness of avant-garde rock heard in Money for Nothing by the Dire Straits.

As their name itself says, these instruments are based on the mechanics of strings, which are usually located within a resonant body and are made to vibrate by various types of sticks or hammers. The piano is obviously the most representative example of this group and, thanks to its slow but constant technical evolution over more than a century, allows for a multiplicity of timbre tones that can make it a valid substitute for the orchestra. In the 18th century, the piano had a clear and crystalline sound such as the one in this Three Voice Invention no. 8 by J. S. Bach (similar to the harpsichord). With the addition of the resonance pedal, the edges of its sound became less defined and even reached, in the so-called “impressionist” period, a colour that was so sfumato as to almost be “turbid” as in Mirrors by M. Ravel. During the 20th century, as a reaction to this aesthetic tendency, which was considered by some to be “degenerate”, the piano re-acquired the percussive sharpness of its original timbre (for an example, listen to Out of Doors by B. Bartók). Of particular interest amongst instruments of popular origin (which are also becoming more common in cultured circles) is the spinet; that strange, trapezoidal-shaped box that we sometimes see being played in the underground and that we can hear in this sample of Un Brin de Bruyère by G. Kurtág.

The members of the bowed string family include the violin, viola, cello, contrabass and all instruments of popular origin or those belonging to other eras and civilizations that are based on the principle of rubbing (usually with a bow) and making taut strings mounted on a resonating cavity vibrate to generate sound waves. The usual use of these instruments is for a lyrical effect (as in the heart-wrenching beginning of the Fourth movement of the Pathetique symphony by P. I. Tchaikovsky), thanks to the expressivity created by the pressure of the bow (which varies the sound volume) and vibrato (which adds warmth and “life” to its sound). These instruments offer many types of sound emissions with varying and surprising results. One of the most outstanding of these is the pizzicato; a technique used primarily in a cultured repertory, however, now also increasingly in a popular repertory (such as in the famous Fourth movement of Peer Gynt Suite no. 1 by Grieg, which also inspired the theme song of a famous television cartoon).