The seventh and final part of our series on electronic percussion examines a few bugs - as well as a few unusual places to stick them.

IN OUR EXPLORATION of Electronic Percussion, we have found ourselves dealing with equipment and techniques that bring the very meaning of the word "percussion" into question. We've been confronted by controllers whose playing is quite alien to the average percussionist, despite the inclusion of the word "drum" in their names. As this quest draws to a close, we return the well-marked trail to rediscover more traditional techniques.

A few months back, we presented an in-depth look at electronic drum pads: how they're used, how they're put together, and why. When we tore one apart, we found very little inside. The actual sensing element was a tiny disc of metal and crystal lodged in the centre of the pad - all the rest was just packaging, more or less. Here, we will investigate what happens when that tiny disc is liberated from its bulky package and used to trigger electronics from acoustic drums.

The Subjects

I OBTAINED PRODUCTS from three different manufacturers for evaluation - the Barcus-Berry Model 2050, the Techtonics Beatmaster SDT, and the Phi Technologies Phi Trac. They have more similarities to one another than differences, so I'll start with a generic description and point out differences as they come up.

First, the transducer itself. As described above, this is a small metal and crystal disc which does the actual "picking up". For those of you who just gotta know everything, the crystal is made of ceramic which has been formulated to exhibit the property of piezoelectricity, in which stresses applied to the crystal cause voltages to appear between its two faces. Connections for bringing out the voltage are made via the metal mounting disc on one face, and a thin film of silver deposited on the other face. Similar technology is at the heart of contact microphone devices such as the Hot Dot. (Barcus-Berry have long been involved with contact-mic products - in fact, the literature accompanying the 2050 deals primarily with its uses in sound reinforcement before going into electronic triggering applications.) Incidentally, piezoelectricity is a two-way thing - voltages applied to a piezo-ceramic crystal will stress and deform it, which is the basis of such things as piezo supertweeters and piezo beepers (more on this later).

The transducer element is encapsulated in some way to protect it and its fragile connections. Techtonics and Barcus-Berry employ the "black goo" method in which the entire transducer and cable are coated in a continuous film of "stuff', while Phi Tech opts for a sealed aluminium can for the transducer. It's worth noting that Phi Tech claim their transducer is capable of withstanding direct stick hits (I can personally vouch for this), whereas the other two manufacturers warned that direct hits would be likely to cause damage. The Barcus-Berry transducer element wins in both small size and low weight categories, but it and the Techtonics would have benefited from a bit of extra beef in the transducer packaging, probably without affecting their performance for most applications. It's true that drummers usually hit the drumhead just where they want to, but accidents will happen... The thin signal cable runs 6-8" to a small housing which, in the simplest case (Phi-Trac) is nothing more than a ¼" jack socket. Standard ¼" audio cables are used to make the connection to the device being triggered.

The principle of such a mic/trigger is that the transducer is small and light enough to ride on a drum head and pick up its vibrations without noticeably changing its sound. It is generally mounted near the edge of the head where its effect is smallest and it is safest from renegade drumsticks. Phi Tech and Barcus-Berry achieve this connection by means of small double-sided adhesive foam rubber pads, which are sticky enough to provide a semi-permanent mounting and thin enough to acoustically couple the transducer to the head, rather than isolate it. (They both come with extra pads, in case you change your mind about the best positioning for the transducer, although the Barcus-Berry was sticky enough to dissuade me from trying to move it, for fear of damaging the transducer.) Techtonics comes with instructions to use insulation tape (bring your own) - however, both of the others grant that insulation tape may be necessary with their units to remedy a troublesome mounting or to provide additional mechanical damping for the transducer itself. Besides, if your supply of those nifty little pads suddenly runs short one Saturday night, guess what you're gonna wind up using instead (two words, first word starts with "i").

Barcus-Berry and Phi also use double-sided adhesive pads to fix the connector holder to the drum shell somewhere out of sight below the rim, without the need to drill holes or otherwise permanently deface it. It is worth mentioning that here too, the double-sided adhesive stuff worked so well as to be virtually unremovable from the drum shell without recourse to some kind of solvent. If your drums have a particularly nice finish, you may actually not want to utilise one of these stick-on pads unless you can live with the connector permanently attached. The holders allow easy removal of the connectors when desired, but these units are clearly intended to stay with their drums when the set is broken down (again, extra points for the durable transducer packaging used by Phi).

In contrast, the Techtonics connector mounts directly on the drum rim by means of a clever spring-metal clip (hence the SDT, or Standard Drum Trigger, is also available as the BDT, or Bass Drum Trigger, with a larger clip for the larger rim of a bass drum). There's a good reason for the rim-mount - the connector is mounted in a small box containing a bat-handle on/off switch and a sensitivity-adjustment knob on top, allowing each pickup to be trimmed as necessary without getting up from the set or turning to face the rack of electronics, as well as providing for the quick defeat of an individual trigger by the drummer. This mounting method also nicely skirts the problems of adhesive pads discussed above - no adhesive anything is applied to the drum shell itself. I was somewhat disappointed to learn that there are no active electronics inside the box. A preamp would have been welcome for a number of reasons, especially in contact-mic applications - the extremely high output impedance of untreated piezo-ceramics makes them a poor bet for sending clean signals in a noisy stage environment, and a poor match for the inputs of most amplifiers as well. The Barcus-Berry literature advises that in sound reinforcement applications, a preamp will be needed for optimum performance.

Of somewhat questionable justifiability is the oversized bat-handle switch used to switch the transducer in and out. Easy to find in a hurry, even without looking - but it's not inconceivable that a wild stick swing might cut the signal off (or even break the switch - drummers are animals). One further departure of the Techtonics unit is that the transducer itself plugs into the control module through a connector instead of being hard-wired. The designer actually says "drummers have a tendency to break things", so this connector makes replacement of the transducer quick and easy. And the cost of a replacement transducer is less than that of a drumhead (although again, carry replacements or you'll be stuck until next Monday). Apart from that, however, it is clear that you wouldn't want to pack up and move a drum set with these modules still attached, as they are relatively large and exposed. The extra connector means that the modules can be quickly stripped from the set without undoing the transducers - a big time-saver, especially if you opt for cement instead of insulation tape on the transducers.

The Tests

TESTS WERE MADE with the transducers plugged directly into the analogue trigger inputs of an electronic drum brain, as well as going into the MIDI inputs of same via a pad-to-MIDI converter. The audio signals were pushed through a 100W amp driving a very efficient PA speaker. This was positioned at the other end of the room, but loud enough (at times) to overshadow the drums as I sat behind the kit - a similar setup to the average pub or club gig.

Just as the trigger pickups are basically similar in design, there were no major differences in performance. The Phi Trac is notable for having an absurdly hot signal output (I almost felt that I could plug it straight into a speaker and hear something). No preamp needed here, at least for trigger applications. Having once trimmed the trigger input sensitivity (or, in the case of the Techtonics, the sensitivity of the trigger itself) however, all units behaved more or less identically. Hence, back to general remarks.

Isolation between drums was not much of a problem. The difference in level between a direct hit on the drumhead and vibration from elsewhere in the kit is quite large, and the latter are insufficient to fire a properly-trimmed trigger input. Literature accompanying the Phi Tech and Techtonics units goes so far as to suggest mounting a pickup on the rim of a drum in addition to the one on the drumhead, making the drum rim a separate trigger device. At extremely high monitor volumes, the triggered electronic sound might be enough to fire its own trigger input, giving rise to the drum version of feedback but in the right hands, this might become the vehicle for an as-yet unseen and no doubt thrilling form of virtuoso performance, I didn't find it easy to achieve - and chose not to sacrifice my eardrums in pursuit of this art.

One problem I did encounter was that of an audible delay between the direct sound of a struck drum and the electronic sound triggered by it. This has nothing to do with the pickups themselves, the delay comes partly from the chain of electronics (I'd guess from 3-7msecs, especially with the pad-to-MIDI converter in line), but mostly from the fact that the monitor speaker was fifteen feet away (that's about 15msec). Another consideration is that of rapid multiple-triggering, which would act to delay the apparent attack of the triggered sound - this was hard to confirm, though. The problem is in one sense unique to acoustic drum triggering, in that "silent" electronic pads don't give the player a sonic time reference against which to hear the electronic sound, even though the actual delays involved are the same, multiple-triggering excepted.

There was one serious problem common to all of the pickups - the response to fast playing was only fair, at best. Again, this is not really the fault of the pickups, but is a consequence of the way in which they are being used. As already discussed, they are basically contact microphones. The output they produce is not a trigger pulse, but an audio signal representing the vibrations of the drumhead to which they are attached. The sound of a struck drumhead goes through very characteristic envelopes of timbre as well as volume: it starts with the sharp stick-impact sound, immediately followed by a rapidly decaying burst of near-white noise, which in turn gives way to a more "tonal" sound as the energy of the stick hit resolves into the resonance of the head. Even when struck rapidly enough for the drum to produce a "sustained" sound, the human ear is able to resolve the individual strokes by identifying the timbre envelopes. To your average drum-brain trigger input, though, this looks like just so much noise. The trigger input cannot recognise timbre information in the incoming signal so only the signal envelope is significant. Ideally it appears as a "spike" similar to that produced by electronic pads, but this is not the case with the output of these acoustic drum pickups. In general, the larger and/or less-well-damped a drum was, the poorer were the results obtained from it.

Stroke and velocity tracking were fairly good on an undamped snare drum up to moderate speeds of single-stroke roll, but pushing it all the way up to "fast" tended to cause irregular response or even outright paralysis of the electronics, because the trigger signal never dropped below the triggering threshold. On the other hand, triggering from a large, tubby floor tom could produce multiple triggers even from a single stroke, because of the time it takes for the head to stop ringing. Adding damping to a drum invariably improved the reliability of the triggering, although of course, the sound of the drum was altered in the process. Ultimately, this method of triggering will be most satisfactory for those drummers who prefer highly-damped drums in the first place, or who are very basic in their approach to playing, making it well-suited to modern dance drumming.

If you're determined to impress the world with double ghost-strokes and single-stick rolls, there is help available in the form of the Simmons MTM pad-to-MIDI converter unit. Unique among such interface boxes, it includes a handful of trigger input processing options aimed at precisely this problem (which, by the way, is the same problem you might experience in a recording situation when trying to replace a drum sound on a master tape, using the original drum recording to trigger the new sound). Acoustic drum triggers place a big burden on the device they're triggering to make sense of the "wall of voltage" which they present at times. Had the Techtonics unit included some active electronics of its own, it might have been in a better position to offload some of this burden (and give itself a bit of an edge over the other pickups in the process). However, a glance at the MTM manual's description of its trigger signal-processing features confirms that neither the problem nor its treatment are trivial. Features such as "dynamic hold-off' (where new triggers are blocked for a varying amount of time, depending upon the velocity of the last hit) and "percent above last threshold" (which allows new triggers to occur even though rapid playing has kept the trigger input signal envelope from dropping down below the normal "idling" threshold level) were not likely to have been squeezed into this little module - at any rate, not without requiring the use of jeweller's tools to make adjustments.

The Other Possibilities

STRIPPED-DOWN AS these pickups may seem when compared to drum pads, there is still one further step possible in the direction of hardware minimalism. As I mentioned earlier, the essential piezo transducer element used in all these gadgets has much in common with a computer piezo "buzzer" element which aren't too hard to get hold of. I am not about to suggest, however, that you should save your money by using these on your drum set in place of one of the pickups discussed above - that extra money buys you a device which is engineered to the task, and a degree of convenience and roadworthiness which only a large amount of tinkering could hope to substitute for.

But, if your needs are not typical, or if you love tinkering for its own sake, then by all means save your money and put some of these little doodads to work. After all, if "real" drum pads can be conceptually reduced to pieces of plastic and rubber with piezo discs on them, it follows that the uses to which these discs can be put in the name of triggering are limited only by your imagination (although I suppose that physical coordination and public-decency laws come into the picture at some point). For a classic example of what can be done in this area, Laurie Anderson's drum-suit dance in her concert film Home of the Brave is required viewing - the most well-known, but not the only, use of this idea.

Another person who has taken some real initiative in this area is Californian Doug Dauz. In addition to his own design of a compact, spring-cushioned drum pad (which is reportedly doing quite well for him), he sent us along a few of his one-of-a-kind creations, some of which are pictured around the text of this article. These include The Boot (for those with an irrepressible urge to tapdance), The Hand (one trigger pad for each fingertip and a comfortable place to rest your palm), The Baseball (keep it in the infield, though) and last but not least, The Disc (strap it on wherever it fits!). It's more fun than working, you know - why not see what you can come up with?

Long may you beat.

Prices Barcus-Berry 2050, £33.95 including VAT; Techtonics Beatmaster SDT, $36.95; Phi Technologies Phi Trac, six for $199.50 (some US dealers will sell individually)

More from Barcus-Berry 2050 distributed by Strings and Things, (Contact Details)

More from The Techtonics Company, (Contact Details)

More from Phi Technologies, (Contact Details)