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In the early 1980s, many manufacturers were beginning to produce polyphonic synthesizers. The VCO designs of the time still left something to be desired in terms of tuning stability. Whilst this was an issue for monophonic synthesizers, the limited number of oscillators (typically 3 or fewer) meant
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For a given capacitor charging current, the amplitude of the output waveform will decrease linearly with frequency. In musical terms, this means a waveform an octave higher in pitch is of half the amplitude. In order to produce a constant amplitude over the full range of the oscillator, some
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The DCO was seen at the time as an improvement over the unstable tuning of VCOs. However, it shared the same ramp core, and the same limited range of waveforms. Although sophisticated analogue waveshaping is possible, the greater simplicity and arbitrary waveforms of digital systems like
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that keeping instruments tuned was a manageable task, often performed using dedicated front panel controls. With the advent of polyphony, tuning problems became worse and costs went up, due to the much larger number of oscillators involved (often 16 in an 8-voice instrument like the
316:, counting pulses from a high frequency master clock (typically several MHz) and toggling the state of its output when the count reaches some predetermined value. The frequency of the counter's output can thus be defined by the number of pulses counted, and this generates a
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of this square wave is used to derive a reset pulse to discharge the capacitor in the oscillator's ramp core. This ensures that the ramp waveform produced is of the same frequency as the counter output.
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A DCO can be considered as a VCO that is synchronised to an external frequency reference. The reference in this case is the reset pulses. These are produced by a digital counter such as the
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This provides stable digital pitch generation by using the leading edge of a square wave to derive a reset pulse to discharge the capacitor in the oscillator's ramp core.
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compensation scheme must be employed. This is often done by controlling the charging current from the same microprocessor that controls the counter reset value.
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from 1981). This created a need for a cheap, reliable, and stable oscillator design. Engineers working on the problem looked to the
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generates a reset pulse, which discharges the capacitor and the cycle begins again. This produces a rising
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This article refers specifically to the DCOs used in many synthesizers of the 1980s . These include the
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The term "digitally controlled oscillator" has been used to describe the combination of a
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Chamberlin, Hal (1985). "Basic Analog
Modules, Voltage-Controlled Oscillator".
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led to most later instruments adopting entirely digital oscillator designs.
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and associated chips that were starting to appear, and developed the DCO.
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configuration. When the capacitor charge reaches a certain level, a
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A common DCO design uses a programmable counter IC such as the
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Russ, Martin (2004). "Early versus modern implementations".
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249:, and this type of oscillator core is known as a
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162:, and is also sometimes used to describe
106:Learn how and when to remove this message
229:Many voltage-controlled oscillators for
375:Musical Applications of Microprocessors
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44:adding citations to reliable sources
164:numerically controlled oscillators
158:driven by a control signal from a
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349:Numerically controlled oscillator
55:"Digitally controlled oscillator"
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320:at the required frequency. The
225:Relation to earlier VCO designs
120:digitally controlled oscillator
31:needs additional citations for
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354:Voltage-controlled oscillator
156:voltage-controlled oscillator
144:voltage-controlled oscillator
390:Sound Synthesis and Sampling
312:chip. The counter acts as a
247:ramp (or sawtooth) waveform
160:digital-to-analog converter
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344:Direct digital synthesizer
217:and its successor Rev2 by
150:Confusion over terminology
260:instead of a comparator.
329:Problems with the design
298:direct digital synthesis
237:charging linearly in an
460:Synthesizer electronics
392:. section 2.6.1, p.137.
136:software-defined radios
455:Electronic oscillators
422:Vintage Synth Explorer
407:Vintage Synth Explorer
219:Dave Smith Instruments
205:, some instruments by
437:STG Soundlabs website
288:of the time and the
40:improve this article
377:. section 6, p.181.
284:technology used in
282:frequency division
267:Historical context
314:frequency divider
286:electronic organs
239:op-amp integrator
213:, and the recent
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322:leading edge
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199:Korg Poly-61
195:Elka Synthex
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38:Please help
33:verification
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318:square wave
215:Prophet '08
126:is used in
449:Categories
360:References
243:comparator
66:newspapers
304:Operation
251:ramp core
235:capacitor
140:analogous
96:July 2018
338:See also
179:Juno-106
173:Juno-6,
175:Juno-60
80:scholar
201:, the
197:, the
193:, the
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171:Roland
142:with "
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211:Kawai
191:JX-10
187:JX-8P
183:JX-3P
87:JSTOR
73:books
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209:and
207:Akai
59:news
124:DCO
122:or
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