Boss DR-110 Cymbal and Hi-Hat Synthesis

PercussionDR-110
Written By Peter Barata

The Boss DR-110 (Dr. Rhythm ‘Graphic’) was a compact and affordable analog drum machine released in 1983. It was Boss’ second drum machine, and their last to be analog.

Despite Boss being a subdivision of Roland, the DR-110 lacks the desirability and prestige of the Roland classics like the 808, 909 or 606. Positioned at the budget end of the market, the 110 offered fewer voices and less customization of the sound. It has just six drum voices: bass, snare, open and closed hi-hats, cymbal, and hand clap. There’s no cowbell or toms. There are no individual outs. And the only sound controls are accent level and a crossfade between emphasizing either cymbal/hi-hat or bass/snare.

Notwithstanding these limitations, the DR-110 sounds great, is vintage, and analog. Its got a nice clap and the cymbal noise is more convincing than on the 808.

Since the service manual is pretty slim compared to the 808 and CR-5000/8000, most of the information below is gleaned from Electric Druid and Richard Curcio’s pages on the DR-110. However, the circuits aren’t too complex, and are easy to follow. The circuit diagram is on page 4 of the service manual (linked below). You can get tuning information for some of the waveforms and envelopes from the checkpoint reference on page 6. Checkpoints 1-4 are the tunings for the cymbal noise. Checkpoints 5 - 14 are various envelope times.

Cymbal Noise:

The DR-110 generates its metallic cymbal noise using 4 square wave oscillators, white noise, and 2 bandpass filters.

The cymbal noise’s primary sound source are 4 NOT gate-based square wave oscillators. They’re tuned to an inharmonic combination of frequencies. According to the service manual, these frequencies were derived from an analysis of real cymbals. All 4 oscillators are mixed together by equal amounts, generating a metallic hum with no distinct pitch.

The tunings from page 6 of the service manual are listed as:

OSC 1 = 0.87ms = 1149 Hz = D6 - 38 cents.

OSC 2 = 1.22ms = 820 Hz = G#5 - 22 cents.

OSC 3 = 3.14ms = 318 Hz = D#4 + 38 cents.

OSC 4 = 2.15ms = 465 Hz = A#4 - 4 cents.

White noise is created with an LFSR (linear feedback shift register). The noise pattern repeats every few seconds. But since this is a drum machine, all of the sounds are shorter than this, and it should go unnoticed. The white noise is mixed with the metallic noise at 1/3rd the volume of the oscillators. The white noise adds a ’tsss’ / hiss that greatly improves the realism of the final sound.

The signal is then split into 2 paths. Each path goes to a different bridged-T based bandpass filter. One path creates a hi-metal noise for the hi-hats and the cymbal’s initial transient ‘ping.’ The other path creates a low-metal noise for the body of the cymbal.

You can find a formula to calculate the centre frequency of the bandpass filters on page 5 (figure 11) of the 808 service manual. These are approximate figures.

Hi Metal Bandpass:

f = 1000000/(2π√(82,000 * 560 * 0.00332 * 0.00332)) = 7,074.261 Hz

Lo Metal Bandpass:

f = 1000000/(2π√(82,000 * 560 * 0.00682 * 0.00682)) = 3,443.775 Hz

Cymbal:

The cymbal sound combines both high and low metal noise sources, routing each through separate VCAs to create two distinct audio paths. The first path generates the initial ‘ping’ of the cymbal’s transient and subsequent decay using the hi-metal source. The second path creates the body of the sound using the lo-metal source.

The ping path uses a composite envelope formed by mixing two separate envelopes. A short 60 ms envelope provides the initial transient, while a longer 900ms envelope creates the decay tail’s hiss at 10% of the transient level. This produces a two-stage decay: an immediate loud decay, followed by a softer, extended release.

After envelope shaping, the ping signal passes through a high-pass filter before reaching the final mix stage.

The body path reuses the same 900ms envelope but modifies it by pumping in extra voltage to extend the duration to 1400ms. Unlike the ping, the body receives no additional filtering.

Both paths are combined at a 2:1 ratio, with the body mixed at half the volume of the ping to create the final cymbal sound.

Closed Hi-Hat:

The closed hi-hat uses the hi-metal noise as a sound source. The signal passes through a VCA that is modulated by an 80ms decay-only envelope.

Open Hi-Hat

The open hi-hat uses the same hi-metal noise as a sound source, but uses a much longer 700ms decay-only envelope.

The two hi-hat sounds interact with each other. When the closed hi-hat triggers, it chokes the open hi-hat by drawing voltage from the open hi-hat’s envelope, shortening its decay time. If both voices trigger simultaneously, the resulting decay time falls at the midpoint between them. When the closed hi-hat fires during the open hi-hat’s decay phase, it can abruptly cut the decay time by varying amounts depending on timing.


Further Reading

Peter Barata
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CR-5000 Cymbal, Hi-Hat, and Cowbell Synthesis