Flute and Piccolo: Flute and piccolo are both woodwind instruments that have light, airy timbres. The piccolo is essentially at a higher octave of the flute, hence the similar timbre. Both instruments produce sound by directing air across a beveled opening at an edge, causing air to split against the edge. This creates the distinctive bright tone of the flute and piccolo.
Trumpet and Cornet: Trumpet and cornet are both brass instruments with bright and piercing timbres. Both instruments produce sound by the vibration of a metal mouthpiece when air is blown through the embouchure. However, the cornet has a slightly softer and mellower sound than the trumpet, due to its lower pitch.
Violin and Viola: Violin and viola are both string instruments that produce soft and warm timbres. Both are played with a bow, which vibrate strings to produce sound. The viola is essentially the lower pitched version of the violin, with a larger body. As a result, the viola has a lower, more mellow timbre.
Cello and Double Bass: Cello and double bass are bowed strings instruments that have resonant and deep timbres. These are low pitched string instruments. The double bass is lower in pitch than the cello, and it produces a lower and fuller sound.