This is one of the most frequently asked questions from our clients. It goes something like this... "Can you arrange this for orchestra?". Let's first define the difference between the two. Sometimes, in a musical theatre setting, the orchestrator can also function as an arranger and vice versa.
The job of an orchestrator is to take the music that the composer has written (usually as a piano-vocal score) interpret it, and notate the parts for individual instruments to play. The individual instruments are decided in advance between the producers and the composer. Some orchestras are as small as 4 players, or can be a full orchestra consisting of over 30 players. Either way, the assignment of notes for each of those players is the role of an orchestrator. Some composers also have their go-to orchestrator who understands their musical language and intent with very little to no explanation or help.
The job of an arranger is to take a piece of original music provided by the composer and tasked with restructuring and reordering sections of music, harmony, and the overall shape and sound of the music. Arrangers in musical theatre typically elaborate on thematic and structural material from the composer. They can also embellish areas where they feel there could be more substance or heighten emotional moments. Someone can also task them with notating new sections of music for a dance break, transition music, scene change music, and other underscoring that occurs outside of the material provided by a composer. An arranger is not always required on a project. This largely depends on the composer's abilities and skills. Most composers do not need the skills of an arranger as they often can make the changes without one or with the help of a music director.
The skills required by these two positions are very different. The orchestrator must have a good understanding and comprehension of the instruments they are writing for and the physics of those instruments. They must also know how the instruments function and what is impossible for a player to play and what will be easier. They also must be able to have an ear and talent for understanding harmonic textures and how to convey the emotional intent through the fabric of an orchestra.
Now, payment for these two skills is billed separately. Some orchestrator's who also arrange and vice versa can negotiate their own flat rate for a project if they are combining both tasks.