Answer:
I believe you can utilize the musical scale "do-re-mi-fa-sol-la-ti-do" made famous in the musical The Sound of Music. As you know, the phrase goes up with each note ending with the second "do". starting with the last note you left off with you repeat the phrase again while still going up the scale. You repeat this for as high as you can go. Each time you complete the scale is considered 1 octave. If you can complete the phrase a second time while still going up the scale it means you have a 2 octave voice. This is why when you hear a singer like Mariah Carey has an 8 octave voice it means she can repeat the phrase 8 times while continuously going up in scale. Most people can do 2 octaves or hit atleast 16 notes. Others with higher octaves can sometime hit notes not found on a piano. Hope that helps.