The SL-1 Analog Bass Synthesizer is a programmable, two oscillator, monophonic synthesizer. Four unique sound presets are available for performance by depressing the MODE button or through MIDI Program Change 1-4 commands. The first preset (VARIABLE) has a complete set of controls that change the various parameters used to control the VARIABLE preset’s sound. The next three presets (TAURUS, TUBA and BASS) have fixed internal parameter values. In normal usage, the VARIABLE preset is set up prior to performance using the front panel controls but may be “played” manually in real-time for extra expression.
The basic tone sources are two voltage controlled oscillators (A and B). Two basic pitch controls are used for fine tuning the instrument. First, the TUNE control is used to set the pitch of both oscillators to the desired reference, such as another instrument being used simultaneously. The BEAT control is used to make fine adjustments in the relative pitch of the two tone oscillators (by modifying the “B” tone source pitch). In addition to these basic tuning controls, the “B” tone oscillator pitch in the VARIABLE present mode may be varied over a greater than one octave range by adjusting the OSC B FREQ control. The relative pitches of the two tone sources are internally set for the three fixed presets.
The instrument may be controlled via MIDI note On/Off Commands or by rear panel analog exponential Control Voltage (Hz/Volt) and S-Trigger inputs. The unit responds to 5 octaves of MIDI note On/Off commands (C0-C5), with Low Note Priority.
The rear panel has MIDI IN and THRU jacks for daisy chaining multiple units. Also, a 4-position dip switch is used to select MIDI CHANNEL 1-16. The SL-1 Synthesizer receives MIDI Note On/Off and Control Change messages only on the selected MIDI channel but passes all MIDI messages out the THRU jack to the next unit. The unit also functions as a MIDI to CV converter to drive other Hz/Volt synths. Rear panel jacks are available for EXPO CV and S-TRIG IN/OUT on stereo TRS jacks.
The pitch of the instrument is controlled not only by MIDI Note On/Off Commands, the TUNE and BEAT, fine tuning controls, but also by a GLIDE control and GLIDE On/Off button. The glide effect is a smooth transition in pitch between successive notes.
The GLIDE On/Off button operates the Glide effect that can be alternately turned ON and OFF, the ON state indicated by the GLIDE LED light being ON. The amount of glide effect is determined by the GLIDE knob position. The player may also control the GLIDE On/Off with MIDI Control Change # 64 (0=Off, 127=On) to switch the effect in or out. In addition, the oscillator A and B frequency can be modulated by the FREQ MOD INPUT jack on the rear panel.
The two tone sources are combined in different amounts in the mixer. In the three fixed presets the amounts are internally set, while in the VARIABLE MODE the relative amounts of the “A” and “B” tone sources appearing in the final output are determined by the OSC B-MIX-A control.
The output of the mixer is applied to the Voltage Controlled Filter (VCF), which may be used to provide either dynamic or fixed timbre modification. Whenever a new MIDI note On event is received, a filter contour trigger signal is generated, successively opening and closing the filter. The amount of opening and closing of the filter cutoff frequency is determined by the FILTER CONTOUR amount knob. The rate at which the filter is opened is determined by the FILTER ATTACK knob amount, while the rate at which the filter is closed is determined by the FILTER DECAY knob position. These filter contour controls determine the dynamic characteristics of the VCF cutoff frequency.
The basic sound of the filter is determined by two other controls (FILTER CUTOFF and EMPHASIS). The initial cutoff frequency is the parameter which is “varied” by the filter contour signal. The initial filter cutoff frequency is determined by the CUTOFF knob. In addition, the cutoff frequency can be controlled by the FILTER INPUT jack on the rear panel. The EMPHASIS control varies the amount of peaking of the filter. That is, the intensity of the frequency components of the oscillator waveforms near the filter cutoff frequency is determined by the EMPHASIS control. An AUDIO INPUT jack on the rear panel can be used to route external line level audio through the VCF and VCA.
The output signal from the voltage controlled filter is applied to the voltage controlled amplifier (VCA). The VCA serves the function of “varying the loudness or volume of the sound”. This is triggered by a MIDI Note On event or by the rear panel S-Trigger input. The rate at which the volume is “ramped up” is called the attack time. This attack time is internally set for the three fixed presets and is set by the LOUDNESS ATTACK control in the VARIABLES Preset. The sustained loudness of the preset is called the SUSTAIN level. The SUSTAIN LEVEL is determined by an internally preset value for the three fixed presets, and by the LOUDNESS SUSTAIN control knob for the VARIABLE preset. In addition, the overall loudness can be controlled by the LOUDNESS INPUT jack on the rear panel. The manner in which the sound dies out or decays is determined by two functions. If the DECAY LED is ON, the sound dies out at a rate determined by the DECAY control in the VARIABLES preset. If the DECAY LED is OFF, the sound dies out immediately when the note is released (MIDI Note Off). The player may also control the DECAY On/Off with MIDI Control Change # 65 (0=Off, 127=On) to switch the effect in or out.
The audio output of the VCA is applied to the OUTPUT LEVEL control on the front panel. The OUTPUT LEVEL control is used adjust the MAIN OUTPUT jack level on the rear panel to match the signal level of the SL-1 to the amplifier or mixer. Generally, the OUTPUT LEVEL control will be set so that the maximum desired loudness for any preset is achieved when both the LOUDNESS and the FILTER contour amounts are at their highest level. When using the SL-1 with an instrument amplifier, plug the SL-1 into the high level “HI” amplifier input, and set the amplifier input volume control one-third to one-half of the way up. Then turn up the OUTPUT LEVEL control on the SL-1 for the desired volume range. WARNING: THIS UNIT CAN PRODUCE VERY LOW FREQUENCY WAVEFORMS THAT CAN PERMANENTLY DAMAGE YOUR SPEAKERS OR AMPLIFIER IF THEY ARE DRIVEN TO CLIPPING.
