120 SECTION FIFTEEN: THE ARP SEQUENCER

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The ARP sequencer has three large, square, white buttons which control its main functions. (See Figure 15-2 on page 121) The right most button starts and stops the sequencer’s internal clock which causes the sequencer to step through its preset voltages. When the sequencer is playing, small lights along the bottom of the sequencer’s panel will light one after the other under each step to indicate that that step is the active step. When a step

becomes active, it sends out the voltage the user preset into it using the slider. In nor- mal operation, the lights move sequentially from left to right from step one to step sixteen.

The bottom left hand button is labeled RESET and will re- turn the sequencer to the first step in the sequence regard- less of where it is in the se- quence. It is interesting to note that the reset button can be pressed while the se-

quencer is playing or while it is stopped. (See Figure 15-3 on page 121)

The top left hand button is labeled STEP and will cause the sequencer to advance one step in the sequence. This is usually most useful when the sequencer is stopped, but like the reset button, this button can be used while the sequencer is playing.

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The way the ARP sequencer is connected to the 2600 depends largely upon what one hopes to accom- plish with it. One obvious application of the sequencer is to use it to control the frequency of the VCOs to produce a preset melodic line. Another great possibility is to use it to open and close the filter in a rhythmic fashion to add life to sounds. The sequencer is equally at home modulating the gain on the VCA so that sounds can get louder and softer in a rhythmic fashion.

Assuming one wants to use the sequencer to control the pitch of the VCOs, one would first connect QUANTIZED OUTPUT A on the upper right hand side of the sequencer to a multiple. The multiple on the 2600 can be used, but the sequencer also has a multiple for this purpose. (See Figure 15-3 on page 121) From the multiple, the sequencer’s CV output signal can then be patched to each VCO using an FM input. It is generally recommended that one use the keyboard CV input on the VCOs, since it would not do to have both the sequencer and the keyboard trying to control the VCO at once. A second reason is that patching into any other FM input would mean having an attenuator between the input and the

oscillator. In Section 2, it was discovered that even when the attenuators on the FM inputs are fully closed, they still alter the incoming control voltage. Other connections can be made to the 2600, but connecting the sequencer to the VCOs will be enough to create a basic sequence.

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When programming a basic sequence, the first step is to decide whether the sequencer will produce one sequence which is sixteen steps long or two simultaneous sequences of eight steps each. This is se- lected using the 16/1 8/2 switch located at the lower left of the panel.

The sequencer actually has two VC outputs, labeled QUANTIZED OUTPUT A and QUANTIZED OUTPUT B. These jacks are lo- cated on the right side of the sequencer’s front panel. If a se- quence is 16 steps long, all of the control voltages the sequencer cre- ates will emerge from QUAN- TIZED OUTPUT A. If two eight- step sequences are being attempted, the left eight steps will be output at QUANTIZED OUTPUT A while the right eight steps will be output at QUANTIZED OUTPUT B.

The sequencer can step through its steps in order (sequentially), or randomly activate steps. This pa- rameter is selected using the RANDOM/SEQUENTIAL switch located on the lower center part of the sequencer’s front panel.

To create a sequence, one must first to create the sound one wants to use on the 2600, and then open the filter and/or VCA so that the patch continuously sounds. The sequencer is stopped (it always starts running when it is switched on), and the RESET button is pressed to return it to the first step in the sequence. The voltage slider on the first step is then moved into the desired position. Assuming that the sequencer is indeed connected properly to the VCOs, a change in pitch should be perceived when the slider over the first step is moved. The STEP button is then pressed, and the next step’s voltage is set using the next slider. This process goes on until all of the steps have been set. The VCA and/or VCF are then closed, and the sequencer is started.

The speed of the sequence can be adjusted by increasing or decreasing the frequency of the internal clock. This is adjusted with the red-capped slider just to the right of the START/STOP button. It is interesting to note that the clock’s frequency can be modulated from an external source. An input and red-capped attenuation slider just to the right of the CLOCK FREQ slider makes this possible.