The Brahms horn trio is a unique combination of piano, violin and horn. The piece's calm beauty was inspired by the death of Brahms's mother (like his German Requiem) in 1865. He was extremely close to her, and began to work on the piece just after she died. When a friend called in on Brahms after his mother’s funeral, the composer was playing Bach on the piano and weeping.
Brahms wrote his horn trio (Op. 40) for natural horn, or Waldhorn. The valve horn was an instrument he learned as a young boy. Using a hunting horn for the piece was partly a way of remembering his early childhood with his mother. This was probably the reason he didn't like the "modern" valve horn, which he thought ruined the special characteristics and sound of the horn. Brahms composed the horn part to add an extra dimension of power in loud passages, and a warmer feeling in the quieter parts of the piece. Its simple sound injects the Brahms horn trio with images of nature.