The Duff Clearing Process

For an in-depth look at the physics behind the
Duff Clearing process, please visit my new WEBook:

Mr. Duff’s Visits with Schrödinger’s Cat
and the Complementary Degenerate

Available at:

The Quantum World of Timpani Pitch: Listening for Order in Chaos

Duff Clearing: Listening for Whole-Membrane Agreement

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 careful adjustment of the tension rods so the drum produces a clear principal tone, a stable pitch center, and an even response around the head.

Clearing is not merely lug matching. Lug matching is one tool in the process, but the real goal is whole-membrane agreement. A head is clear when the principal tone is stable, the preferred modes support that tone, and the drum behaves as one membrane rather than as a collection of isolated lug points.

Below is a brief synopsis of the key points in the Duff clearing process.

Objective: adjust the membrane so that each lug area supports the same principal tone, allowing the drum to produce a clear, sustained, musically stable pitch.
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.
Place the drum on a platform so that your ear is level with the head.
Tune to a pitch in the middle range of the drum and use a hard stick when striking the head.
Place a small mute in the center of the drum to reduce the center-active concentric response and help the ear focus on the principal tone. Mute other drums to avoid sympathetic vibrations.
If a drum has eight lugs,* the Duff process can be understood as a four-point, two-channel check. There will be two sets of tuning quadrants. Each quadrant-set will have two channels: primary and secondary. Lugs directly in line with the beating spot are in the primary channel. Lugs perpendicular to the beating spot, orthogonal at 90º, are in the secondary channel. (see diagram below)
The primary channel has more influence on the pitch at the initial strike, while the secondary channel influences the pitch during the sustain and decay, especially if the drum is struck loudly.
As a working diagnostic rule, if the sustained pitch rises after the initial strike, the primary channel may be flat and may need to be raised.
As a working diagnostic rule, if the sustained pitch flattens after the initial strike, the secondary channel may need to be raised.
With the drum set to the middle of its range, strike the drum three times softly, listen, pause, and then strike once loudly and listen.
The soft strokes reveal the local principal tone at the striking spot, or primary channel. The loud stroke engages more of the membrane and helps determine whether a lug is sharp or flat in either the secondary channel or the other quadrant-set.
Do not chase the overtones. Listen through them and focus on the principal tone. Mode (2,1), the fifth, may sound attractive because it sustains, but the clearing process depends on stabilizing mode (1,1).
Adjust lugs accordingly by making quarter turns only. This allows you to return the lug easily if the adjustment does not improve the sound. Use eighth turns as the clearing progresses.
Lugs work in pairs, so remember to check the opposing lug in both the primary and secondary channels.
Adjust only the channels within a quadrant-set as you move around the drum using the cross-lug tuning sequence. As you test the pitch with loud and soft strokes at each rod, if the pitch goes slightly sharp or flat, it is most likely one of the tension rods in the primary or secondary channel. If the overall clarity of the pitch is muddy, the quadrant-sets are not matched.
When a soft stroke and a loud stroke anywhere around the circumference of the drum produce an even pitch and resonant tone at all dynamic levels, the head is clear.

* If a drum has five, six, or seven tuning lugs, the secondary channel or channels, and sometimes the opposing lug of the primary channel, will fall between two lugs. Adjusting these channels must be balanced between the two lugs adjacent to where the channel falls naturally. This type of head clearing is certainly more challenging, but it can be achieved. Cloyd Duff’s 32″ Anheier Cable Drum seven-lug drum has long been regarded by some players as one of the finest-sounding drums of its type. See Clearing a Six Lug Timpano.

** One must be mindful not to 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. A bright quality can be mistaken as sounding sharp, while a dull quality can be mistaken as sounding flat. Pitch and tone quality must be heard separately, and with practice, that ability can be cultivated.

The soft/loud stroke test is especially useful because it asks whether the drum behaves as one membrane. A soft stroke can reveal the local principal tone near the playing spot. A loud stroke engages more of the membrane and can expose disagreement between the primary and secondary channels. If those channels do not support the same pitch center, the drum may seem close at individual lug points while still sounding unstable in real playing.

Fig. 1 (click to enlarge)

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, while 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. There is no single rule; much depends on the integrity of the head itself, the choice of primary playing spot or spots, and the number of lugs a drum has. See the discussion of personal preferences.

Most modern calf heads, such as those made by Kalfo-VELLUM & PARCHMENT WORKS LTD, Maynooth Rd, Co. Kildare, Naas, Ireland, +353 1628 82 70, are homogeneous enough to have multiple usable playing areas, so strict adherence to older mounting practices is not always necessary. Players often rotate their heads once a favored playing spot becomes tired and worn.

Synthetic heads do not have a backbone, belly, hip, or neck area in the same biological sense as calfskin, but they still develop preferred playing areas through seating, collar formation, tension history, and wear. The channel logic of Duff clearing remains useful because the player is still testing whether the head behaves as one membrane. Skin heads vary biologically; synthetic heads vary through manufacturing, seating, and tension history. Both must be cleared as membranes, not as isolated lug points.