ARP2600 - Fundamentals of Music Technology - Cyborgstudio.com

SECTION3VCO-2A FIRST LOOKIn Section 2, a basic voltage controlled oscillator (VCO-1) was discussed in detail. In this section,VCO-2 will be examined. Although VCO-2 is more complex than VCO-1, all of the things that weresaid about VCO-1 apply to VCO-2. VCO-2 can be thought of as the ‘super oscillator’ on the ARP 2600since it is the most flexible, and thus the most powerful oscillator of the three found on the 2600. Thefirst thing one notices when looking at VCO-2 for the first time is the additional waveforms thatVCO-2 can produce. In addition to the saw wave, VCO-2 can produce sine, triangle, and pulse waves.SINE WAVESSine waves (see Figure 3-1) have a very pure sound, becausethey have only one harmonic, and that is the fundamental.CD track 07 It is also important to note that whilethe square and saw waves that VCO-1 produced ranged between0 Volts and +10 Volts, the sine wave VCO-2 producesranges between -5 Volts and +5 Volts. Overall, it still has thesame amplitude span as the waveforms VCO-1 produced,but because it dips into negative voltage, it is more flexible.When the sine wave output is used to modulate anothersource, it can actually send a negative value to that carrier,rather than just a positive value. This technique will be exploredin depth in a later section.+10V+5V0V-5V-10VtimeFigure 3-1: A sine waveTRIANGLE WAVESTriangle waves (see Figure 3-2) sound a little buzzy, butsmoother than a saw wave. Although they look very similar+10Vto a saw wave, they are actually most like square waves harmonically.CD track 07 Just like the square wave, they have+5Vonly the odd numbered harmonics. At first, this doesn’t seemtimeto make any sense. If the harmonic content of a waveform0Vdetermines its shape, and the triangle and square waves bothhave the same harmonics, shouldn’t they look alike and sound-5Valike? Actually, it is possible for two different waveforms to-10Vhave the same harmonics present, but present in differentamounts. In the triangle wave, some of the upper harmonicsare present in higher amounts than in the square wave. ThisFigure 3-2: A triangle wave gives it a buzzy sound which is different from the squarewave. It is also important to note that like the sine wave, the triangle wave ranges from -5 Volts to +5Volts, meaning that it can send a negative value to a carrier when it is being used as a modulator.018