Sorcha. I dont know what kind of instrument you play, but if it is a stringed one you can, for example, tune the instrument two semi-tones lower and play as if you were playing "C". You will then be playing in B-flat. If the instrument is a guitar, you can put a capo on the third fret and play as if you were playing in "C". The result will be playing in "E-flat".

Murray