7.0

mVCO 

Introduction

The name "mVCO" you will not find in standard synthesizer module language. The most closest would be VC-LFO (Voltage Controlled Low Frequency Oscillator) but because the mVCO also can generate frequencies within the audio range. I decided to make up a new name that would distinguish it from other modules. VCMO sounds a little strange and thus it became mVCO.

As the "M" indicates it is an oscillator for modulation purposes and not to generate audio frequencies to be heard as tones in a final musical output (although it is possible).

The reason to also have the mVCO produce audio range frequencies lays in the concept that when the response time of AM and FM inputs is fast enough you can create much more effects.

Wave Forms

The mVCO has two outputs. The SQR TTL output delivers a squared wave form at a so called TTL level (0 to +5V swing). This TTL level makes it easy to use the SQR also for 'clocking' digital inputs (such as the S&H and SEQ input controls and external logical controls such as Trigger, Gate and Sync controls).

With the WF control pot (Wave Form Control) you can set the so called Duty Cycle of the SQR. The Duty Cycle is the ratio of the time that the SQR is at low and at high level within one period. You can vary the Duty Cycle from 1 to 99 % - from a short pulse up to a short pulse down. In the middle position of the WF control the Duty Cycle is 50/50.

The TRI/SAW output delivers a Triangular, Saw Tooth or Ramp wave form - depending on the WF control pot (Wave Form control). In the most left position you will have a Ramp wave form (fast rising and slow falling), at the middle position a Triangle wave form (equally rising and falling) and in the most right position a Saw Tooth wave form (slow rising and fast falling). Thus you can set the wave form anywhere between these main shapes

Frequency Control

With the FREQ control you can set the frequency.

Frequency range

With the RANGE selection switch you can set the frequency range that the mVCO can swing from minimum to maximum control voltage.

• LF: Low Frequency range.
• AU: Audio frequency range.
• VLF: Very Low Frequency range

FM (Frequency Modulation)

With the FM input and FM control you can modulate the frequency with an external voltage. This voltage can be any signal - either from the TD or an external source. Either (semi) static (keyboard), low frequency or audio frequency.

Use

The use of the mVCO in combination with the other modules of the TD are many. By internal connections the outputs of the mVCO already are connected to inputs of the other modules.
The SQR is connected to the FM controls of both fGenerators via the FM select switch to produce a two-step sequence of tones (the base tone and a higher or lower tone at each cycle of the SQR wave). Of course it depends on the frequency of the mVCO and the FM depth how things may sound.
Also, when the fGenerators are in "Cross Mode" the mVCO could slightly control on a low speed one of the FM inputs to prevent the fGenerators to lock on to each other.

The TRI/SAW output of the mVCO is internally connected to the AM function of both fGenerators (via the AM selection switch). This can produce Tremolo effects or, when the frequency of the mVCO is set to audio range, ring modulation like effects.

The SQR of the mVCO also is internally connected to the HLD (hold) input of the Sequencer to function - when the Sequencer is set into HLD mode - as an automatic 'hold' generator (best at low frequencies) to generate pseudo random Sequencer patterns.

Wave Form Control

Hence that the setting of the WF control is important to generate all kind of variations and effects for certain patches. Remember that the WF control both effect the TRI/SAW and the SQR outputs.

8.0

INVerters 

Introduction

Two independent so called inverters are available.
An inverter just inverts (mirror) the input signal. Positive becomes negative and vice versa. For audio signals this is not effective under 'normal' circumstances but, for control signals the effect can be rigorous.

INV 1 is internally connected to the ENV output and just produces a negative output. When the ENV is set to function as a Synthi-drum envelope signal generator then, the effect of the inverted signal may lead to an opposite function. For example a down going tone instead of a up going one. The output of the INV 1 is so to say a mirror of its input with a negative polarity.

INV 2 is internally connected to the LOG 2 unit and thus produces a mirror with a negative polarity of the LOG 2 output voltage. Thus, the INV 2 output would let a tone go down instead of going up if used for FM control of the fGenerators.

Use

You can use the INV units for any signal path to have it inverted. It can deal with both AC and DC signals (thus both audio and steady or low dynamically changing voltages).

The only thing you cannot do is to invert a TTL level SQR and then use it as a logic control for the S&H or SEQ units. This is because these logic control are based on a positive SQR and the INV unit would turn it into a negative voltage based SQR --> thus no response.

You very well could use the inverters to interface with other devices. Both to invert analogue control signals and to bring logic levels to its proper polarity level (invert plus and minus and vice versa).

9.0

LOG converters 

Introduction

The LOG converters - also known as exponential generators - are at first instance meant to function as an interface to convert a linear V/OCT voltage from a keyboard to an exponential voltage to have the linear fGenerators respond properly to a keyboard scale.

V/OCT

V/OCT means Voltage per Octave. Each Octave distance represents a difference of 1 Volt. But, a linear voltage controlled oscillator needs to be controlled with a doubling of the control voltage for each octave to jump up. The V/OCT output from a key board delivers 0,1,2,3,4 Volts for a range of 5 Octaves. A linear generator then need to be controlled by 0,1,2,4,8 Volts to generate these octave scale.

Tuning

The LOG units are build up with a classical design. This also implies that they are quite temperature sensitive and thus they may get out of tune a little when the temperature differs much from the normal chamber temperature (21 degrees Celsius).

At the front panel there can be two adjustable controls found which can be adjusted with a small screw driver. They are tuned in combination with the fGenerators to create a proper frequency scale when a keyboard is used with a V/OCT output.
It might be that you have to slightly readjust the ADJ controls in combination with the keyboard that you are using.

Input

The input range of the LOG unit has an input range from 0...+10V.

Negative input voltages are not converted.

Output

The output of the LOG unit ranges from 0 to +5 Volts and is routed to the FM2 and FM4 inputs of the fGenerators. These FM inputs are adjusted - when the FM control is fully set open - to create a proper keyboard tuned scale.

Other use

You also can use the LOG units to transfer any other wave form to a logarithmic one, with respect to the fact that the negative part of a signal is simply cut off.
When you route the ENV output signal to a LOG unit, then the LOG output will produce a curve which might suit better for the use of AM of FM control. I say might, because it is a matter of taste.

When you feed the LOG unit with the TRI/SAW output of the mVCO you can create interesting variation of the wave forms.

When you feed the output of a fGenerator to the LOG input you transform it also like just said for the mVCO but since you are using this output for the final audio signal you will hear tones in a different timbre. Thus the LOG unit functions as a wave form shaper.
When the fGenerators are in "Cross Generate" which means that the output signal of each generator is with a cross link brought back to the AM or FM input of each other - then inserting the LOG units into this 'cross feedback' signal paths can be very effective too.

10

Quantizers 

Introduction

A Quantizer is a unit you hardly find in classical analogue modular synthesizer design. It is typically an unit which can be seen as an extension to make things more easy from the point of view of a tuned tonality.

An example of this ease is: to always set a tuned tone with a Sequencer because the Quantizer always rounds the Sequencer output voltages to the nearest tuned tone. This in contrast to try to do this without a Quantizer because then you need to have a absolute hearing and also manage to turn the control voltage knob for each Sequencer step exactly to tune each tone. A Quantizer overcomes this problem by always delivering an output voltage which produces a tuned tone (when connected to control a VCO with a V/OCT input).

As a second example: when the S&H unit delivers a random stepped voltage and you control a VCO with this, you then get a melody pattern which is really random - no tuned melody pattern. When using the Quantizer to have the control voltage quantified, you then are able to produce a tuned random or pseudo-random melody.

Also, the TD Quantizer does have possibilities for alternative use. They will be discussed at the end of this Quantizer item.

What does a Quantizer do?

A Quantizer transforms an analogue input voltage to an exact defined output voltage according a certain resolution. For the purpose of controlling modules of a modular synth, based on a VOLT/OCTAVE (V/OCT) principal in combination with a tonality principal of 12 tones within one Octave, this leads to a Quantizer which delivers a 12 step per volt increase or decrease.
Thus, the TD Quantizer rounds (quantifies) an analogue voltage input to a value which is at closest to a 1/12 Volt scale.
This linear 1/12 Volt per step output gives you the possibility to achieve a tuned tonality although the control voltage origin (the input voltage of the Quantizer) may have an infinite amount of voltage variations.

The principal of 12 steps per Octave (per Volt) implies that each step (note) requires a voltage change of 1V/12 = 0.083 Volt. By first digitizing the input voltage and then convert it back to an analogue value - according a certain output scale - this is achieved (AD/DA conversion).

S&H Quantizer

The output voltage of the S&H unit is routed to a Quantizer to round the S&H output voltage to a value which jumps only according a 12 notes / Octave system and therefore the Quantified S&H output delivers a random or pseudo-random melody voltage pattern.
When the quantified output also is used to (parallel) to control a VCF frequency, then the frequency shift of the VCF is tracking exactly with the frequency shift of the VCO and this is important to keep a certain filtering steady over a certain octave range.
But, it also might be valuable to have a VCO be controlled by a quantified voltage to guaranty tonality and having the VCF controlled by the raw voltage and thus being able to have some headroom in the filter characteristics of the filter relative to the exact tone/filter ratio.

Outputs

The S&H unit thus has two outputs.

• The analogue output - named "P" from positive - although it also can deliver a negative voltage (positive means here the relative phase).
• A quantified voltage output - named "Q" which delivers a 12 notes per octave rounded voltage round.

When you are using the S&H output voltage to control parameters which are not implying the need to round up to a 12 step/Volt (12 notes/Octave) principal, you then do not be concerned about rounding the voltage. Nevertheless, it might be interesting to also use the quantified output because it makes sure that you can reproduce a certain patch and control setup more easily because the control voltage is determined exactly rather than being floating anywhere between 1/12 step/Volt.
On the other hand: creating patches and setting which not always might be exactly reproducible is the charm of the TD as a whole and has its own value in context to the sound you like to produce.
Thus: it depends on your aim whether you will use the quantified output and/or a combination with Q and not-Q control voltage of the S&H unit.

Advantages of having a Quantizer for the S&H unit.

A S&H circuitry stores a sample of an input voltage (momentary value) into a so called capacitor. This C-element functions as a analogue memory cell. The disadvantage of analogue technologies in this context implies a loss of memory over time. This means that when you are using a very slow CK rate to refresh the S&H output voltage, you will be confronted with a voltage drop. When using the S&H normal output (not quantified) to control a VCO, this means that you will hear the tone go down very slowly because the analogue memory cell is leaking. When using a 'normal melody' CK rate, you hardly will notice this but when you have a CK rate of once per 10 seconds you will.
A Quantizer which is clocked by the S&H Clock does not have his problem because the analogue input value is digitized immediately and as such stored into the digital memory of Quantizer. Thus the resulting output voltage after conversion back to an analogue voltage again remains stable over an infinite time period.

SEQ Quantizer (Patchable)

The second Quantizer can be externally patched. Internally via de input it is connected to the "P" output of the Sequencer. Thus, when not an external patch is made the second "P" output is Quantified and available at the "Q" output. This Q output is internally routed to the FM4 input (FM of the second fGenerator). By this you directly can generate Sequencer melodies which are tuned when the FM4 control is set at maximum.

Quantifying (Sampling) rate

In contrast to the Quantizer of the S&H, the 2nd Quantizer continuously is sampling the input (the Sequencer output voltages when not rerouted by a patch). I could have set this sampling rate at 50 kHz and so have created a Quantizer which also can quantify an audio signal - applied to the Quantizer input, but that would not much of a use. The audio signal only would sound distort with odd harmonics because it would a analogue signal based on a 7 bit digital conversion.

Much more interesting is to set the sample rate at a frequency in the low area of the audio range. Then not only it would operate as a Quantizer for slow signals but also as an effective modulator for audio signals. The audio signal then would have a frequency limit equal to half the sampling rate and a higher frequency would be degraded to this half sampling frequency. Related to the terminology of samplers we could say that - for audio signals - "under-sampling" is done instead of the usual "over-sampling".
The sampling frequency is set at approx. 1 kHz (1000 Hz). Thus till 500 Hz (1000/2) an over sampling is done but the more closer to the 500 Hz the frequency of the audio signal gets, the less it get and the more modulation can be heard. When exceeding the 500 Hz, the modulation becomes strong and starts to sound like a ring modulator effect - modulated with a 500 Hz carrier frequency.
Whether using the 2nd Quantizer for audio modulation/distortion purposes depends on your taste and further treatment (filters for example). Experimenting here is the clue to use this characteristic of the 2nd Quantizer to achieve a special sound.

Patching

You can use the second Quantizer for many setups because you can external patch the input and output.

First let’s see what input signals from the TD itself could be used. Keep in mind that the output internally still is routed to the FM4 input of the 2nd fGenerator to control the tone height.

Alternative use

This part will handle some possibilities for using the Quantizer unit for alternative sounds/effects.

Modulating signal

When you apply a slow changing signal to the Quantizer input ( for example the triangle wave form from the mVCO) and use the Quantified output to modulate the tone height (internally connected to the FM4 input of the second fGenerator) then, instead of a tone that goes up and down fluently within a certain range - set with the FM pot depth) the tones will jump - tuned to a 12 NOTES/OCT scale when the FM4 pot is turned fully to its right. Of course, turning the FM4 control pot to the left and thus decreasing the FM depth will have the tones step up or down less than a note.

When you set the frequency of the mVCO higher, it becomes more and more an effect. The modulation signal is now super imposed onto the ground frequency of the fGenerator and due to the quantizing character it will respond differently than when not being quantified. The FM4 depth control plays an important role here. Thus, when experimenting with this setup: play with the depth.

Delayed S&H signal

When you first patch the S&H output to the LP unit and set the SLOPE pot for some delay of the S&H signal and then use this LP output to connect to the Quantizer input then, the Quantizer output will follow the S&H voltage pattern with some delay. When using both normal S&H quantifies output and delayed output of the 2nd Quantizer to control the two fGenerators, you get a S&H hold melody from the 1st fGenerator and delayed followed pattern from the first. Again, you need to experiment with this setup and play with the delay time (SLOPE) to find setting that are practical to be used.

Envelope stepping

Using the ENV signal to feed the Quantizer and then using the Q output to FM control a fGenerator has the effect that instead of a tone which goes fluently up or down will jump tuned notes. When the ENV unit is controlled by a Synthi-drum pickup element or a microphone the amplitude of the pickup in combination with the control settings of the ENV (Attack/Release) will result in a tone scale going up and/or down per half a note.

Now it depends very much how you interface and act to create something useful. When - for example - you have created a 'drum' pickup which can deliver a signal (either AC or DC) which represents the strength of your beating on the element, then you can play a melody and/or a melody up and down going sequence.

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