You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Classical_music

Context:
It is in this time that the notation of music on a staff and other elements of musical notation began to take shape. This invention made possible the separation of the composition of a piece of music from its transmission; without written music, transmission was oral, and subject to change every time it was transmitted. With a musical score, a work of music could be performed without the composer's presence. The invention of the movable-type printing press in the 15th century had far-reaching consequences on the preservation and transmission of music.

Question:
What was oral music subject to every time is was transmitted?

change