Berlioz is probably most well known for his innovations in the use of the orchestra. In his "Symphonie Fantastique" (1830) we see Berlioz stretch the common practices of the time through his addition of new instruments, his incredibly detailed performance directions and mostly his wholly unique programmatic exploitation of the orchestra. It is not only the range of instruments that Berlioz includes that is notable; it is also the level of detail that he puts on the score and way in which he uses his instruments to achieve unusual effects all in order to express his program. .
Berlioz introduced several new instruments in the "Symphonie Fantastique" including: the ophicleide, cornet, Eb clarinet, cor anglais harp and bells. It is interesting to see Berlioz use these instruments for specific programmatic reasons. For example in the second movement (Un ball) Berlioz uses the harp to create the atmosphere of a glittering ball and represent the experience of the "festive crowd" described in the programme. Moreover, Berlioz uses the ophicleide, a traditional marching band instrument, in the fourth movement (March au supplice) to create a military sound relatable to the audience. However his most striking use of the ophicleide is the repulsive sound created in the 5th movement Dies Irae theme in the very low register doubled by bassoons for programmatic effect. In the fifth movement (Songed'unenuit du sabbat) Berlioz uses the Eb clarinet to transform the pleasant sound of the Idée Fixe to one appropriate to the programme: "The beloved melody reappears once more, but it has lost its noble and modest character; it has become no more than a vulgar dance tune, trivial and grotesque; She is coming to the SabbathShe joins in the diabolic orgy". The Eb clarinet captures this idea to an incredible degree of effectiveness as its shrill and piercing tone quality transforms the Idée Fixe to a mockery of the initial theme.