You’ll need to do this to truly understand his voice and his character in general. Make note of the subtleties and nuances in his voice. Note the type of words he uses, phrases he says often and how he relates to others. Who better to learn how to mimic Cartman’s voice, than from the voice actor himself? Replay his videos a lot. Observe how he holds his mouth, how his jaw is positioned, how his tongue stays flat when saying most words, etc. Cartman has a slight lisp and tends to jumble letters together. Instead of saying, “Cool!” and pronouncing all the letters in the word, Cartman says, “Ku!” He also tends to speak from behind his teeth. For example, when saying the word “tomorrow,” he pronounces it, “Tuh-muh-ruh.” He’s a loud talker and often sounds like he’s yelling at everyone, even during normal conversations. Remember, Cartman is still a kid who hasn't gone through puberty so his voice is really high. He also sounds super nasally which is a distinct sound. Notice as well that when he speaks it almost sounds like he has marbles in his mouth.  Practice by squeezing your nostrils closed to imitate the voice. Notice the squeakiness in his voice too. This is especially noticeable when he’s crying. The pitch is the noise created based on the rate of vibration of the vocal folds. The sound of the voice changes as the rate of vibrations varies. Meaning, if you want your voice to sound higher pitched like Cartman's, you will need to train your vocal cords to tighten and/or relax, depending on your natural sound. Computer software can be used to manipulate your voice as well. While Trey Parker does a great job on his own creating the iconic sound, his voice is further altered by technology to produce an even more extreme pitch.
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One-sentence summary -- Watch a lot of South Park episodes. Watch Trey Parker demonstrations. Understand his accent. Listen carefully to the voice. Hone in on the pitch.


Find a therapist that has experience treating OCD or related disorders. Search by either asking your regular physician, getting a referral from family or friends, or try using this handy psychologist locator from the American Psychological Association Make sure that this is a person you feel comfortable with and has the credentials required to meet your needs. It is important to see a professional for diagnosis, as there are other problems that have similar symptoms to OCD. Your physician can refer you, but a qualified mental health professional should conduct the diagnosis. There are two groups of OCD symptoms, obsessions and compulsions. Obsessive symptoms are constant, tenacious and undesirable thoughts, impulses or images that trigger feelings of anguish or apprehension. You may feel thoughts or images keep popping up even though you try to avoid them or shut them down. Compulsion symptoms are the behaviors that you perform in order to cope with the concern linked to obsessions. These are the behaviors that supposedly prevent the fear from coming true, and they often appear as rules or rituals. Together, obsessions and compulsions create characteristic patterns like the following:  Those who fear contamination and the spread of dirt, usually have cleaning or hand-washing compulsions. Others repeatedly check things (that the door is locked, or the oven is turned off, etc.) that they associate with potential danger. Some fear that if everything isn't done just right that something terrible will happen to themselves or loved ones. Many become obsessed with order and symmetry. They frequently have superstitions about certain orders and arrangements. Then, there are those who are afraid that bad things will come if they throw anything away. This makes them compulsively keep things around that they do not need (like broken objects or old newspapers). This condition is called Compulsive Hoarding. To be diagnosed with OCD, you must have obsessions and compulsions on most days for at least two weeks. Alternately, you may be diagnosed with OCD if your obsessions and compulsions have a significant impact on your daily life (for example, you are so afraid of germs that you wash your hands so often they bleed and you cannot touch anything that is outside your house). This sort of therapy focuses on exposure and response prevention (ERP), which means that your therapist will expose you to the things that you fear or obsess over, and then will help you to come up with healthy ways to cope with these anxieties. Therapy sessions may consist of one-on-one sessions, family therapy sessions, or group sessions. This may be a process of trial and error, and in some cases, you may find that a combination of drugs are more effective at combating your symptoms than one drug by itself.  A commonly prescribed type of drug is a selective serotonin reuptake inhibitor (SSRI), like citalopram (Celexa), fluoxetine (Prozac), paroxetine (Paxil), and escitalopram (Lexapro). These drugs increase the activity of the neurotransmitter that helps balance mood and lower stress (serotonin).  Another regularly prescribed drug is the tricyclic antidepressant (TCA) clomipramine, which has been approved by the FDA for treating OCD. SSRIs are usually prescribed over clomipramine because they have fewer adverse side effects.  Never stop taking any medication without consulting the prescribing doctor. This can cause a relapse of your symptoms and withdrawal-like side effects.
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One-sentence summary --
Choose a therapist. Get a diagnosis for OCD. Work with a psychotherapist to control your compulsive behaviors. Talk to your doctor about finding a suitable medication.