The Behringer 921A Oscillator Driver works in conjunction with the Behringer 921B Oscillator module, and both are based on units from a famed 1970s modular synth system. Using the 921A Oscillator Driver, you can alter the frequency of the 921B Oscillator module according to semitones or octaves, selectable with a rocker switch. Additionally, the 921A outputs an adjustable rectangular waveform for pulse width modulation. The 921A is CV-controllable with two summed inputs each for frequency and pulse width, for wild moving modulations. And, unlike the original 1970s unit, the 921A isn’t constrained to affecting one oscillator unit; Behringer has designed it to drive up to 12 parallel oscillators. Synthesists at Sweetwater have enthusiastically hopped on the Eurorack bandwagon, but, for the Eurorack-curious, it can sometimes seem like a costly and confusing endeavor. But, the Behringer System 100 Eurorack modules, including the Behringer 921A Oscillator Driver, are an affordable, simple, and incredible-sounding way to enter the exciting world of Eurorack!