The Duff Clearing Process
One of the most widely used methods for adjusting timpani heads is a process used by Cloyd Duff who was timpanist of the Cleveland Orchestra from 1942 until 1981. It is a method he called clearing and it involves a process of persuading the partials to more closely match those of a true harmonic series by careful adjustment of the tension rods.
Below is a synopsis of the key points in the Duff clearing process.
1. Objective: tune the membrane so that each lug is in-tune with the others allowing the drum to produce a clear sustained pitch.
2. Quiet space and patience are needed for extremely focused listening. Clear in increments of ten minutes and then take a break to rest the ear.
3. Place the drum on a platform so that your ear is level with the head.
4. Tune to a pitch in the middle range of the drum and use a hard stick when striking the head.
5. Place a mute in the center of the drum to dampen high overtones. Dampen other drums to avoid sympathetic vibrations.
6. Two channels: lugs directly inline with the beating spot are in the primary channel. Lugs perpendicular to the beating spot are in the secondary channel. (see diagram below)
7. The primary channel will have more influence on the pitch at the time of the initial strike while the secondary channel will influence the pitch during the sustain/decay, especially if the drum is struck loudly.
8. If the sustained pitch rises after the initial strike, the primary channel is flat and needs to be raised.
9. If the sustained pitch flattens after the initial strike, the secondary channel needs to be raised.
10. Place the drum in the middle of its range. Strike the drum three times softly then listen, pause and then once loudly and listen.
11. The soft strokes will give you the basic principal tone at the striking spot, while the loud stroke will help determine whether a lug is sharp or flat in either the primary or secondary channel.
12. Ignore the overtones and focus on the principal tone only.*
13. Adjust lugs accordingly by making quarter turns only. This is so you can easily return the lug if it does not improve the sound.
14. Lugs work in pairs so remember to always check the opposing lug.
15. Work in channels or quadrants as you move around the drum. If the pitch goes sharp or flat, it is most likely one of the tension rods at the channel perpendicular to the spot you are striking, which is in the secondary channel. If it is off a great deal, it is probably one of the tension rods in the main channel.
* One must be mindful to not confuse pitch with tone. No two points around the circumference of the drum will have exactly the same tone quality, but they can still have the same pitch. i.e., a bright quality can be mistaken as sounding sharp while a dull quality can be mistaken as being flat. Pitch and quality must be heard separately and with practice, the ability can be cultivated.
Figure 1 is the hypothetical mounting of a calf head for the drum to the direct right of the player. For this particular head, Area “A” on the neck proved to be the best playing spot. Backbone placement varies from player to player. Some place the backbone so it bisects the drum at lug points, others offset it a small amount. Some players prefer to mount a head so that the belly area is the primary striking spot. Others feel that the hip area usually has the best playing spots. No rules, just personal preferences; much depends on the integrity of the head itself, choice of primary playing spot(s), and the number of lugs a drum has (see below). Most modern calf heads (Kalfo) are homogeneous enough to have multiple playing areas, so a strict adherence to past mounting practices is not always necessary. Players often rotate their heads once a favored playing spot becomes tired and worn.