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Drums – Microphony Made Easy

3/16/2012

 
Fig. 1. While recording this tamtam, the author wrapped the mic in a towel and coiled the cable to minimize handling noise.

MICROPHONES ALLOW us to hear and record sounds that are otherwise imperceptible to the naked ear. Just as a doctor uses a stethoscope to listen to a patient’s cardiopulmonary system, a recording engineer can use a mic to explore an instrument for unique sounds.

The vibrating body of an instrument produces numerous localized spectral components that can only be heard when a listening device is in very close proximity. By focusing on specific areas, we can capture unusual harmonic combinations that change over time, and enhance the effect by moving the microphone by hand while we record. In this article, I will explore this idea using cymbals and gongs, which offer harmonically rich timbres that are fun to work with.

Good Vibrations An instrument’s timbre is defined by the resonating characteristics of the materials from which it is built. The 19th-century physicist Ernst Chladni demonstrated the vibrational modes of solid surfaces by bowing the edge of a metal plate that was covered in a fine layer of sand. As the surface resonated, the sand formed into patterns that showed the positions of the nodes and anti-nodes at a specific resonating frequency. Search for the term “Chladni” on YouTube and you’ll find videos that demonstrate this phenomenon and give you some insight into why you’ll hear different sounds as you move a mic over a vibrating surface.

The definitive example of this miking technique is Karlheinz Stockhausen’s classic work Mikrophonie I for tam-tam (a type of gong with a flat center) and six musicians. (Two musicians play the instrument, two move microphones, and two process the sounds in real time.) The impetus for the work came when Stockhausen used household objects to play a large tam-tam he had acquired. While he scraped and tapped the instrument, he moved a handheld microphone over the surface to pick up the complex resonances being produced, while a colleague filtered and recorded the sounds that the microphone captured. Although the initial experiment was improvised, Stockhausen went on to compose a piece that utilizes metal, wood, rubber, glass, cardboard, and plastic to excite the tam-tam’s surface, ranking the types of sounds created from low and dark to high and bright. The technique can be performed on just about any object that resonates, and the method used to excite the instrument plays a role in the sounds you’ll hear.

Close Miking Although the attack of various materials and playing techniques are interesting, an instrument’s decay characteristics can be just as fruitful. The trick is to move the mic in as close as possible to the cymbal or gong as the vibration decreases. Your ear will guide you to the right spots if you monitor the mic input through headphones.

Any microphone that is easy to hold and move can be used. The main thing to avoid is handling noise, which is generated at the mic or by cable movement. You may have to wrap the mic body in something that mitigates the noise, such as a towel or soft foam (see Figure 1). You should also coil up a portion of the cable in your hand so that the cable doesn’t scrape against anything.

Mic type and polar pattern play a major role in what you’ll hear. If the mic has a directional pattern, you can focus more precisely on interesting timbres. However, you will also get an increase in lower frequencies due to the proximity effect. If that bothers you, try using an omni pattern.

Spend time finding the sweet spot on the instrument. Each playing technique will excite different vibrational modes in different parts of a gong or cymbal. Don’t simply put the mic over the area you’re playing. Try hitting the edge of the gong and moving the mic around the center of the instrument. Or tap the center and move the mic slowly to the edge and back again to exaggerate the timbral shifts the instrument offers as it decays.

Explore Dynamics Typically, the harder you hit a cymbal or gong with a wooden stick, the higher the harmonics you’ll hear. As the sound decays, the timbre gradually changes as the higher harmonics fade. I often find the sustaining portion to be as interesting as the attack, and I look for ways to excite a tam-tam or cymbal that help it sustain longer, such as using soft yarn, rubber, or wool mallets. Hitting it with a knuckle or closed fist can produce darker tonalities that shift subtly.

You can elicit higher harmonics without resorting to loud hits by tapping or scraping the instrument gently with a blunt piece of metal, such as a triangle beater or bolt. (Pick something that doesn’t damage the instrument.) Another technique is to place the open end of a paper tube flat against a gong and scrape it. When done correctly, it generates a shriek that is rich with harmonics.

You can get a similar effect by dragging the head of a drumstick flat against the surface of a cymbal, or by using a violin or cello bow on the edge. Pulling a superball, stuck to the end of a chopstick, across the surface will produce a variety of high-frequency tones, depending on how hard you press down and how quickly you move.

Envelope Moving the microphone quickly towards and away from the instrument helps shape the envelope of the sound. The results can be a tremolo effect that includes spectral shifts, and the father away from the instrument you go, the deeper the effect will be. You can also move the mic toward a different spot each time you get close to the cymbal.

My favorite envelope shape involves rushing the mic towards the instrument immediately after it’s struck, then gradually slowing the mic movements as the instrument decays (the opposite of the way a ball would bounce off the ground). Non-linear, arrhythmic mic moves yield the most interesting results, though moving the mic in time with the beat is also nice.

To exaggerate the decay or create a reverse envelope, add a compressor in the signal path. A high ratio and slow decay will further transform the sounds.

Gino Robair writes about and teaches audio recording in the Bay Area. Check out his music at ginorobair.com.
 
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