Contrabass oboe

The contrabass oboe is a double reed woodwind instrument in the key of C or F, sounding two octaves or an octave and a fourth (respectively) lower than the standard oboe.

Current research, in particular that by hautboy specialist Bruce Haynes, suggests that such instruments may have been developed in France as part of an original attempt to maintain the complete family of double reed instruments when the oboe was created from the shawm. There was an instrument referred to as the basse de cromorne or basse de hautbois which was used by Lully, Charpentier, and other French Baroque composers. This apparently was an oboe-type instrument in the bassoon range. It had, nonetheless, a distinct tonal quality of its own. Richard Strauss states, in his edition of Hector Berlioz's Treatise on Instrumentation, that its tone "...had not the slightest similarity with the low tones of the bassoon."

Despite this distinction, the contrabass oboe never became popular or widely used, and few remain today.

...
Wikipedia