One of the major components to any Humorous Interpretation are vocals.  Vocals are used not only for humor purposes but for characterization as well.  All characters must have a distinct voice which is clear, consistent, and a good representation of who that character is.  Though the definition of vocalization is fairly basic, vocals are anything but.  Defining multiple personas' voice with the vocal chords of one is ambitious.  It takes practice, dedication, and WORK.  Blindly trudging forward with the development of a vocal range is admirable.  However, here is some guidance on the subject.

Reference your script. As you create your Humorous Interpretation characters it is important to keep them in tune with the intentions and heart of the script.  And finding a voice is easier when you understand the character.  Analyze their lines and interpret what sort of character they are.  Look for personality traits and sculpt an image of who that person is.  Once you have an idea, try to connect that image to your established prior knowledge; "this character reminds me of..."  Further, a character with a prominent style of speaking could suggest a particular vocalization.  For instance, a character with complaints for lines could have vocals that sound whiny/nasally to vocally reflect the annoyance of their speech.

Look to television and film for accents. Reflect on films or television shows you have seen with accents unlike those on your circuit.  An accent is a quick fix to expanding your vocal range, and TV and film can be a great way to learn an accent.  Honestly, watching nothing but BBC America for a week will have you imitating the English with ease.  Just be careful to not overuse accents in your Humorous Interpretation or to do a poorly imitated accent (when not intended for comic effect).  Accents take practice, so find sources of quality accents, watch, and start speaking!

Your next voice could be sitting next to you. EVERYONE around you has a unique vocal pattern they use in daily speech, and if you stop chatting and listen you can hear it.  Pay attention to the voices around you, and get some ideas for how to add individuality and range to your Humorous Interpretation's characters.  Remember though that if you choose a familiar voice, such as a coach or teammate, that it can be hilarious unless taken too far and turns harsh.  Be careful.

LISTEN. In order to increase your vocal range through imitation you need to be quiet and listen.  Close your eyes; shut down all your other senses except for hearing.  Focus only on sound.  Take it in and memorize the quality.

Record yourself. If you have a tape recorder use it!  Recording your vocalizations for Humorous Interpretation is an effective way to hear precisely what your current characters sound like.  By recording and creating a subjective way to analyze your vocal range you have a better chance of quickly expanding your abilities.

Avoid stereotype traps. Humorous Interpretation stock characters are common (Geek, Gay Guy, Cheerleader, Jock, etc.).  Everyone is going to use one; it's unavoidable.  However, if you use a stock character voice as a base for your character and then add twists based on interpretations found in the script you can successfully dodge a stereotype trap: generic vocals.  Attention to physicality and differentiating yourself with your body is another way to avoid becoming a generic stereotype.

PRACTICE.  PRACTICE.  PRACTICE. And keep trying new things.

How vast your Humorous Interpretation vocal range grows ultimately depends on how well you train your voice.  The more time you spend playing with noises and sounds, the more likely it is your range will increase.  It's that simple.  What time you put in is what you will get out.  Of course, some are gifted with the ability to master voices quickly (Hank Azaria comes to mind), but even they must practice.  Go forth and start talking in tongues; your Humorous Interpretation will thank you for it!