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6

such a signal is called a 

 

square 

 

wave. As the knob is rotated 

in either direction from vertical, the pulse becomes wider (to 
the right) or narrower (left).

3. When this switch is moved to the right, VCO 2 is SYNCHRO-
NIZED to the frequency of VCO 1. VCO 1 is not affected by this 
switch regardless; but VCO 2, when it is "sync'd" to VCO 1, can 
produce only harmonics of the frequency to which VCO 1 is set. 
When the switch is off the two oscillators are completely inde-
pendent.

4. These are the three MANUAL CONTROLS for the filter. The 
smaller knob at the lower right determines whether the filter 
will act as a 

 

bandpass filter 

 

(at the click-stop position

labelled "BP"

 

), lowpass filter 

 

(immediately clockwise from the 

click-stop, labelled "LP"), 

 

notch filter 

 

(vertical, at the word 

"notch"), or 

 

highpass filter 

 

(extreme clockwise, labelled 

"HP"). Do not try to turn the knob clockwise past the highpass 
stop.

The large vernier control at the upper left determines the fre-
quency at which the filter begins to take effect, or the 

 

center 

frequency 

 

of the bandpass and notch modes. In the low- and 

high- pass modes the frequency at which the filter begins to 
have some effect on a signal passing through it is called the 

 

cutoff frequency 

 

of the filter.

The large single knob labelled RESONANCE determines the filter 
resonance at its cutoff frequency. When this knob is fully 
counterclockwise the filter resonance is at a minimum; as it is 
rotated to the right the resonance increases. RESONANCE is a 
term for the gain (i.e. roughly, 

 

loudness) 

 

of the filter at or 

near its cutoff frequency. At maximum resonance, for example, 
the filter amplifies strongly any components of the input sig-
nal that lie within a semitone or so of the cutoff frequency, 
but virtually ignores components that are not near the cutoff 
frequency.

In other words, a pronounced "peak" occurs in the filter fre-
quency response as the resonance is increased, which grows 
higher in amplitude as it grows narrower in width. When the 
center of this peak is exactly at the frequency of an audio 
input to the filter, a relatively weak signal can drive the 
filter to produce a quite strong output.

5. The switch selects one of three sources for a control input 
to the filter. The left and right positions are self-explana-
tory;

 

 

 

the center position carries a signal from the SAMPLE/HOLD 

section of the mini-sequencer panel. This signal is independent 
of any of the routing and assignment switches in the 

Summary of Contents for Two Voice

Page 1: ...A BRIEF INSTRUCTION MANUAL for the OBERHEIM TWO VOICE SYNTHESIZER prepared by james michmerhuizen director the boston school of electronic music...

Page 2: ...is on voice module two will not be gated until a second key is depressed 3 The PORTAMENTO control normally left fully counterclock wise introduces a lengthening pitch slide between different notes on...

Page 3: ...king the external connection to headphones or ampli fier you may turn the synthesizer on Locate the ASSIGNMENTS switches in the minisequencer section and be sure that they are all down In each voice m...

Page 4: ...scription following applies to the three switch version The first switch on the left selects the source of control voltages and gates for VOICE MODULE ONE In its lowest posi tion voice module one will...

Page 5: ...nt of LAG low frequency filtering applied to the sample hold voltage Turning the lag control to the right produces in other words the same effect on pitches being governed by the sample hold that the...

Page 6: ...he three position switch selects one of three control signals indicated on the panel to be routed through the rotary pot just above the switch If this knob is rotated to the right the selected control...

Page 7: ...ter begins to have some effect on a signal passing through it is called the cutoff frequency of the filter The large single knob labelled RESONANCE determines the filter resonance at its cutoff freque...

Page 8: ...ctly to the output of the NOISE GENERATOR that is part of the sample hold in the minisequencer Noise filtered in various ways is used in the production of wind thunder and motor sounds as well as many...

Page 9: ...e NOTE above In order to simplify the operation of the voice module while learning or whenever it is necessary to hear continuous sound this VCA BYPASS SWITCH can be moved to the on right position Thi...

Page 10: ...nual pulse width controls of each oscillator note that these have no effect on the sawtooth oscillator outputs and finally with the VCF manual controls for frequency resonance and pass mode Do not at...

Page 11: ...by voltage control you are changing the range or area of particular frequencies that are emphasized Try using maximum resonance with a lowpitched sawtooth input open only a little about 10 o clock an...

Page 12: ...s the filter frequency down as it is rotated to the right the ENV 2 signal drives the filter frequency up d as the filter resonance is increased its output level will generally increase Compensate by...

Page 13: ...nd sustain and fairly short decay Now slight changes in the filter frequency control in the range 12 o clock to 3 O clock will produce a wide range of percussive noises In a later section you will lea...

Page 14: ...dinary and conservative results however will come from playing con tinuous legato on the lower voice and a slight nonlegato on the upper voice E TROUBLESHOOTING I Using only the controls we have intro...

Page 15: ...t s how we started you off the VCA BYPASS switch on and the filter open If either of these conditions does not hold then no continuous sound is possible except that with certain envelope settings unde...

Page 16: ...o change the pitch of the oscillator The on off switch for the minisequencer CLOCK has also a lower position labelled step This position is spring loaded and the svitcb will not stay there but every t...

Page 17: ...nspositions will occur with the depression of only a single key if one key is held down while another is depressed to the right of it the sequence will transpose to the higher key only for as long as...

Page 18: ...trol of the s h begin with the two knobs in the s h section rotated maximum counterclockvise and slowly increase the range setting The first voice produces a series of random pitches over a wider and...

Page 19: ...all four to check 4 The beat frequency will always double as you go up by octaves So after you have tuned at 8 go up to 4 and then 2 to check on the tuning of each oscillator read just if necessary If...

Page 20: ...fective range 3 As you increase the filter resonance beyond about the eleven o clock position begin to decrease the audio input levels to the filter until at maximum resonance the audio input level s...

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