This is a strange member of the oboe family. It is the only true mezzo-soprano voice in any woodwind family. In this, I think it best to discuss what a mezzo-soprano actually is. In the vocal world, a mezzo-soprano is a soprano voice that has a timbre similar to a contralto. This fits the Oboe d’Amore perfectly. It is pitched in A, a minor third lower than the Oboe. Unlike the Oboe, the Oboe d’Amore does not possess a low B-flat, so its bottom note is a sounding G-sharp which is only a major second below that of the Oboe. We use the Oboe d’Amore in truth only for a timbral difference, and not one of pitch extension.
That said, it is a useful instrument and has a personality all its own. In sound, it is midway between the Oboe and the English Horn as one would expect. Professional oboists have described the sound of the d’Amore to me as being “electric.” There is a zing in the sound that isn’t apparent in either of its neighbors.
It is used in some well-known orchestral pieces, like Bolero, but as far as I know, it has never made an appearance in the band. This is a shame. Most universities will have access to at least one d’Amore (often, two are required in several works by Bach).
Technique-wise, the d’Amore can do pretty much anything that the Oboe can. Many well-known parts ascend all the way to the top F of the instrument, although one questions the use of the d’Amore in such an extreme register.
The Bach Concerto for Oboe d’Amore
The opening of the 6th Movement of Havergal Brian’s Gothic Symphony (opens with d’Amore).
Ravel’s Bolero. Viennese Oboe d’Amore at 4:05. Note, Viennese oboes are very different than those used elsewhere, and produce a more strident sound.