How to explore and develop character voices
If you're already an actor, you'll have a natural interest in tuning in to the voices of other people. You will be a ready listener. There is a complete joy in catching snippets of conversation in the street; on the train or bus; in a queue for the cinema; in a cafe or a bar; anywhere you can casually catch snatches of other conversations.
As you listen, try and catch a (private) view of the mouth of the voice that has attracted your attention. Have a look at how the lips are used... Are they tight, pursed and tense? Or might they be animated and expressive? Are the teeth clenched, with the vocal sounds emanating from behind them? Is there an over- or under-bite that affects the vocal sounds produced? Is the entire face of the speaker animated? Pay attention to the volume of the voice, too. If it is very quiet or careful, why would that be? Likewise, why would anyone wish to produce a particularly loud sound as they speak - what does that say about the person behind the voice? The angle of the neck will also have a bearing on the production of the speaker's voice: is the chin held back, into the neck, or does it jut out? Is it held high so that there is unecessary pressure on the back of the throat, for example? So much to observe and take in for future use.
Obviously, the physicality of a real-life character will have a bearing on the vocal sound produced, also. Pay close attention to the way the chest is held; the stomach; the shoulders; the age of the speaker. As an actor, you will know that all these areas of interest have a distinct bearing on vocal production and by utilising these individual observations, to recreate sound, you will realise that character work starts with the body, then can be transposed to the voice.
Really, really listen with specific purpose. If there is an accent that interests you, whilst you are watching your chosen real character, completely tune in to the vowel sounds produced. They provide the keys to mastering useful accents and dialects. Think about where the tongue goes when you listen to the production of those vowel sounds. Does the sound emanate from the roof of the mouth or is it placed at the mouth sides; or at the back of the throat, or even deep within the throat? What happens to the lips? Watch with an actor's eye and listen with an actor's ear. You have to watch while you listen. The clues are always there to observe.
Especially tune in to the intonation that your chosen character is employing. Is it an expressive voice? How many vocal notes are being used or does the voice stay within only two or three pitches in a flat delivery? Does it define 'monotone'? Why? what does that inform you about that person and his/her life?
When you are alone, have a go at producing what you have already heard and logged. It will take a great deal of repetition to get some way towards reproducing the sound that interested you. Look at your mouth in a mirror as you speak. Is your mouth being used in the manner that you observed? Your neck? Your body? Are you stepping away from your own vocal habits? From where are you producing the sound? How does it make you feel?
If you have regular contact with someone who has a different accent or dialect to your own, try and hear as much of that person speaking as you can. Encourage them to tell you stories from their past. For example, I worked with a woman from Derry (Northern Ireland) for quite some time and can now produce that very specific accent with no problem, having immersed myself into the particular sounds she naturally produced. It is - really - just tuning your ears in differently to very specialised, focused listening. It's not just about the words used (though different dialects use unique vocabulary), it's about how the vocal sounds are manufactured. And, as always, practise practise practise.