A call maker typically bores a sound channel from the exhaust port end of the insert through the bell all the way through the insert. A newer innovation was to drill the sound channel to a specific depth in the sound board, but stopping before reaching the tip of the sound board, thus creating back pressure and making the call easier to blow. By drilling the sound channel to just past the seat line, a call maker may then complete the shaping of the sound channel after the forming of the sound board using an end mill to cut a precisely shaped channel with controlled angle, depth, and width to adjust the proper root back pressure and finely tune the calls tone and quality in a replicable manner.
