How would changing the proportions of substance in an alloy change its properties?

An alloy is a mixture of two or more metals which is produced with a specific proportion between metals. So, if the proportion is changed the physical characteristic would be changed as well. For example, brass musical instruments are made of brass which is a mixture (an alloy) of zinc and copper in a specific proportion. If you change a proportion, you will change the physical characteristic of brass musical instruments, and a sound they produce will be different.