In a medium saucepan, combine sugar, water, cranberries and raspberries. Bring to boiling; reduce heat to medium. Simmer, uncovered, about 5 minutes until all the cranberries have popped. Remove from heat and allow to cool to room temperature. Pass through a fine mesh sieve, pressing lightly on the fruit with the back of a large spoon. Do not press too hard or your syrup may become cloudy. Transfer syrup to a pitcher or bottle; cover and refrigerate until ready to use. Syrup may be refrigerated for up to 2 weeks.