I use Fruit Fresh mixed in the syrup. I am not sure how much ascorbic acid is in each tsp. The container tells how much to add per cup of syrup. I will have to look before I can tell you.
Most folks just use it to soak the fruit in, they put the fruit in water and add it. I don't do that. Even if the fruit starts browning as it sits once peeled and slice, they come back to being totally fresh and bright once in the syrup with the Fruit Fresh. They stay that way the whole time, after they are canned. The flavor is fresher, too.
Oh, here you go :
If ascorbic acid products are not used in the pretreatment of cut fruit, they may be added to the canning juices or liquids before processing. This will help keep the fruit from darkening during storage. Use 1/4 to 1/2 teaspoon crystalline ascorbic acid or 750 to 1,500 mg crushed vitamin C tablets per quart of fruit. Commercial ascorbic and citric acid mixtures such as "Fruit Fresh" or "ACM" also may be used according to manufacturer's directions.

When I canned peaches, I always use ascorbic acid, and its also useful if you freeze them as it helps to hold the color and prevent browning. Because the canned ones seem to get a bit of brown right close to the lid, I fill the jars with the hot peaches and no sugar syrup, then sprinkle about a half to one teaspooon per quart jar on the surface. When they get processed, the ascorbic acid dissolves and mixes itself in. The surface has the most concentration unless you shake the jars, but they do seem to hold the color a bit longer when I do it that way. Ascorbic isn't as tart tasting on it own, compared to citric, so you can use as much as you feel is necessary. Even mixing in most of it with the syrup, then a sprinkle of more on top before capping can also help. Vitamin C pills have constarch or other binders, and are not as pure as the granulated stuff. I mistakenly bought a big one pound bag of ascorbic, but found out it wasn't a food grade. They also use it to reduce downey mildew on the leaves of garden plants.