Module Description Controls & Ins/Outs
lfo1.jpg (44321 bytes)

LFO-NZ VC-LFO / Noise

INTRODUCTION:
An LFO module with 2 separate waveform outputs out of a choice of 4.
Use an LFO to control a VCO (to create vibrato), a VCA (for tremelo)
or to control a filter's cut-off frequencer (wah-wah /filter sweep).
Use it any where you want to change a module's performance over time.

SPEED:
This sets the LFO frequency

RAMP / REVERSE RAMP LEVEL / SELECT SWITCH:
Sets the output level to the Ramp out jack of the Ramp signal. Pull the control out to select Reverse Ramp.

TRIANGLE / SQUARE LEVEL / SELECT SWITCH:
Sets the output level to the Triangle out jack of the Trianlge signal. Pull the control out to select Square
Inputs: Outputs: LFO Controls:
Frequency
CV 		Ramp/
Reverse
Ramp

Triangle/
Square

Noise

Speed

Ramp/
Rev.Ramp
Level

Tri/Sqr
Level

Switches: Power: Indicators:
Push/Pull
switches
built into
level pots
select which
waveform is
affected by
the level
control and
is output at
socket.

+/- 12V

Size:6HP

 

LFO Frequency

Controls

S+H Lag
This adds slew (or portamento) between each changing voltage held by the S+H.

Noise Level
Alters the noise level.

LFO Waveform
Selects the waveform that is fed through the Delay circuits:

S+H (Sample and Hold) , Noise, Sawtooth, Reverse Sawtooth, Square, Triangle, Sinewave.

LFO Freq
Sets the frequency of the LFO.

Range
Coarse setting for the LFO frequency. Shifts the range of the Freq pot in 3 steps.

LFO Delay
Alters the LFO delay time. Note, for this function to work, a trigger must be fed into the DEL TRIG socket.

LFO Level
Sets the final output level of the delayed LFO signal.

Sockets

S+H In
This is the signal source for the S+H. Normally the noise output would be used for a randon output.

S+H Clock In
Each clock or gate pulse will make the S+H sample the input signal then hold it till the next clock signal. Normally a square wave signal would be fed into here, like the LFO1 square wave output.

S+H Sig Out
This is the output from the S+H unit. This is also fed into the S+H posisition on the LFO Waveform switch.

Noise Out
This is an audio output from the noise generator. This can be fed into the S+H signal input for random S+H.

LFO Reset (RST) In
When a positive voltage is fed in here, the LFO waveform will reset, so it will restart its waveform cycle from zero.

LFO Delay Trigger (DEL TRIG) In
When a positive voltage is fed in here, it will activate the the delay feature, so the LFO signal coming out of the DEL socket will be delayed for a period set by the DELAY pot.

LFO Frequency CV (FCV) In
A 0-10V control voltage can be fed in here to control the LFO frequency

LFO Delay (DEL) Out
The delayed LFO signal is output here.

LFO Waveform Outs (triangle, reverse saw, saw, square)
The direct and individual waveforms are output at the sockets.

The Low Frequency Oscillator (LFO) In More Detail

The LFO gives a control voltage in the shape of a waveform. It is basically an oscillator which generates a cyclic waveform at low frequencie below the audio range.

The LFO can produce different waveshapes used to modulate various other modules. Common uses of LFO modulation are to obtain vibrator (by modulating the pitch of a VCO), wah-wah (by modulating the filter cut-off frequency), tremelo (by modulating the gain of a VCA).

Some LFOs can have there frequency voltage controlled like with a VCO. Some have a reset input. When a gate or trigger signal is received at the reset input, the LFO waveform will be reset to zero, re-starting its wave cycle. Rarely found on LFO modules is a Delay time setting in conjunction with a Delay trigger input. The Delay adjusts the rate it takes the LFO signal to go from zero to full intensisty, initiated by a gate or trigger signal at the Delay trigger input.

Modulation is the most vital consideration when using the synthesiser as an electronic musical instrument. Why? Sound is not music, merely a carrier of information. It is the change in sound that our ears perceive as music; our brains, via our ears, are good at detecting and assessing these changes and thus sound is merely the carrier of musical concepts.

Modulation is the business of making changes to the constituent elements of sound, so really if we are to accept the above paragraph music and modulation sources go hand in hand. Below we will go into detail of the major modulation source in an electronic music synthesiser - the low frequency oscillator.

Low frequency oscillations are defined as periodic vibrations at frequencies below the audio threshold. You will all be aware of the fundamental ideas behind oscillators and voltage control. The LFO cannot act as a sound source, it is a modifying element that is used to process and control other elements of the sound. The ‘low’ in LFO defines the oscillator as operating at frequencies below the audio threshold, which for most of us is around 30Hz.

If we examine the LFO in its simplest block diagram format, below, it can be seen that it is a source signal, i.e. the LFO is not reliant on any other input such as CVs or triggers; it produces a periodically varying output CV that is purely a function of the front panel LFO rate control. This isn’t always the case, though, as there are some more advanced LFOs that can be controlled themselves.

But to continue with our simple LFO, it is generally the case that it will provide triangle and sqaure wave output signals at rates between 0.01 up to about 30Hz. In some cases you will find that the LFO produces sine instead of triangle waveforms - this is in fact preferable, but it was the case that manufacturers found it more expensive to incorporate sine wave generators into their instruments and consequently we often have to make do with the sharp edges of the triangle wave. This isn’t too horrific a proposition,as one has to listen quite closely to the modulated signal to detect its nature, however of course, in the audio spectrum the difference brought about by the higher harmonic content is considerably more noticeable.

In the more eleborate LFOs a wide range of additional waveform outputs and features are provided - ramp andpulse in particular.

The Role of the LFO

The most common use for the LFO is pitch or frequency modulation. Sine or triangle wave modulation of the VCOs is known as vibrato, square wave modulation as trill. Gernerally frequency modulation applied via the modulation performance controls (wheels, ribbons, joysticks or whatever), however it is possible to permanently route the LFO to the VCO if it is so desired, though the effect is generally rather monotonous for musical apllications.

Vibrato is generally applied so that the pitch deviatioon is less than plus or minus a semitone, applied around the initial frequency of the oscillator, the overall modulated sound output retains its original tuning.

However trill is the oscillation between two steady frequencies. The square wave oscillates between a zero volt level (which has no effect on the pitch of the VCO) and a positive value, which determines the upper note to which the trill is set.

The other use of the LFO in conjuntion with the VCO is to provide a control signal with which to modulate thepulse width.

Sine or triangle modulation of the filter goes by various names, the most common and unlikely being that of ‘growl’, though sometimes the terms ‘wow’ or ‘wow-wow’ appear. LFO modulation of the filter is less commonly utilised, as musically it is not as important as vibrato or trill; however, iti is often useful when routing the LFO to the oscillators, to parallel the signal to the filters in order to enhance the effect.

LFO modulation of the VCA usually employs either sine or triangle wave for tremelo effects or the ramp down waveform which can be used for similated echo effects.