SamplecrazeStretch That Note

Synthesis - Part 7

So, welcome back to another instalment in the ‘ongoing, hell, when’s it ever gonna end?’ synthesis tutorials.

In this tutorial I want to cover a few quite important parts of analogue synthesis, notably: sample and hold, sync, cross modulation, keyboard tracking, and velocity.

Sample and Hold S/H or S & H

This is the periodic `capture' of a frequency along a dynamic waveform which is held until the next `sample' is taken. The S/H module is used to capture a signal's voltage level and hold it until the next voltage is input.

What does this mean in simpler terms? It means that the S/H function is used in creating voltage sequences, either in repeating patterns (with lower values) or random patterns (with higher values). And what does what I just wrote mean? It means turn the damn knob and listen to what happens. Haha. Seriously though, the S/H is one great feature and most commonly used as a modulator, even though it itself can have more than one source triggering it. It is normally governed by the clock generator that sends out pulses, but this is in most modular systems whereby the S/H module sits alone. You can actually assign anything into the S/H input, and in most cases oscillators are used and patched into the S/H module. However, the most common source for the S/H is the noise waveform. On some synthesizers, these two are hard patched together and you can apply varying amounts of noise to the input signal. However, oscillators are the most commonly used sources.

Be funky and assign an oscillator to the S/H, which is then patched to the filter cut-off, or resonance, and move the knob and you will hear the undulating effect that the S/H creates. Used on very high rates, the S/H starts to randomise the destination. This makes for some really deep and serious pitch mangling, great for mad effects or interesting textures. Actually, think of a car siren in Dance music. This is a great example of S/H being used with a sine wave and pitch.

Other little funky trick is to use saw, S/H on a high value, and noise. You get burbling and spluttering effects.

I love using S/H on a very small value and have it modulate the pitch of an Lfo. This makes for a nice moving, undulating texture. Lovely for spacey sounds and film score type of music.


You know what the word sync means in general terms. So, let us apply it in terms of this subject matter.

When you sync one oscillator to another and use the first oscillator as the synchroniser, or master, and the receiving oscillator as the slave, or receiver, what takes place is quite simple really. As we know, oscillators behave in cyclical fashion, ie, they have cycles, the waveforms repeat themselves (cycles). When the master completes one cycle it then resets the slave to start it’s cycle again. Let me explain that in simpler terms with an example. If you were to take a sine wave as the master and a saw wave as a slave, then every time the sine wave completed a cycle, the saw wave would start it’s cycle. Since we know that cycles determine frequencies, then it’s obvious that the slave would be running at the frequency of the master. The new waveform that is formed will be a combination of the contour of both waveforms (oscillators) but at the frequency of the master waveform.

A good test for ‘hearing’ sync is to detune 2 oscillators and listen to them. They will sound wide and fat. Now hit the sync button and the sound suddenly behaves itself and sounds straight. It’s hard to explain, but once you have tried it you will understand. Of course, sync does have it’s benefits and can be used to create layered sounds or simply to create a new waveform from 2 existing ones.

Cross Modulation

Is where the pitch of one oscillator is controlled (modulated) by another. However, what is crucial here is that the modulating oscillator’s pitch is determined by pressing a note on a keyboard. In effect, the voltage of the key pressed determines the pitch of the modulating oscillator. This, in turn, modulates another oscillator. Press a note and the oscillator fires up and the pitch of the fired up oscillator then modulates the other oscillator. This is sometimes referred to as FM (Frequency Modulation). This is why FM synthesis is so cool for creating those bell-like sounds, weird and wondrous pads and metallic sounds. Yamaha made their name with FM synthesis, thus the DX7 was made a legend.

If you look at the hierarchy and terminology used in FM synthesis, the first 2 things that will jump out at you are Operator and Modulator. That should give you a clue as to what takes place in FM synthesis.

I intend on writing a tutorial on FM synthesis as it is so alien to so many people. It is a form of synthesis that seems to perplex beginners to programming as there are not only operators and modulators but algorithms as well. Sounds complex , but once you get the hang of it, it is one serious form of synthesis.

Keyboard Tracking

Keyboard Tracking is also known as Keyboard Follow or Keyboard Scaling.

The simplest, and it really is simple, way to describe this term is to just say that the keyboard acts as a modulator.

Basically the keyboard can be the source for a number of different destinations, that is, of course, in terms of it acting as a modulator. Apart from the standard pitch control of the notes, the keyboard can be set to control all manner of destinations. I love modulating the filter cut-off or resonance with the keyboard. I patch the keyboard in such a way, so that every time I play ‘up’ the octaves, the filter opens and the sound gets brighter. If I play ‘down’ the keyboard the filter closes. This is actually called ‘Filter Tracking’. But you can modulate other events. A very common form of Keyboard Tracking is to have the keyboard control amplitude. As you go up the keys, the notes get louder and vice versa. Synthesizers that have a more detailed modulation matrix, will, invariably, yield more complex, powerful and varied results. In most cases tracking is achieved with positive and negative values and, in some instances, with percentage values. The positive and negative are simple on/off messages and are the mainstay of subtractive synthesis. However, even in this domain, we can assign values. Today’s synthesizers have far more detailed programming tools and the keyboard can be used to modulate so many different destinations. A good example would be panning. I have often programmed my Emu sampler or Proteus 2500 to modulate pan depending on how hard I hit a note (Velocity) or if I go up the keyboard. If I hit the note above a certain threshold, the sound pans to the right, if I hit the same note below a certain threshold, the sound pans left. If I play above C3, the sounds pan right. If I play below C3, the sound pan left.

Today, we are spoilt with the amount of power that synthesizers offer us.


Velocity simply means how hard a note is struck.

But in today’s world of potent synthesizers, velocity can be one serious weapon.

We can assign velocity to a number of destinations and have velocity modulate any or all of them. The pan example I gave above is one of countless destinations you can have and you are only limited by the strength of your synthesizer’s modulation matrix.

I could write pages on some of the destinations that velocity can be assigned to, but let me explain the standard default destination that today’s synthesizers are programmed to. Amplitude is the most common destination for velocity modulation. The softer you play the keys, the quieter the sound. The harder you play the keys, the louder the sound. The amount of ‘quietness’ or ‘loudness’ is usually determined by a value above or below a threshold, both can be set by the user. This is often referred to as Amt. You will see this word often, but as a suffix to a source or destination. Vel amt is a good example. If you play hard, you are, in effect, going above this threshold and the amplitude rises. Drop below this threshold and the amplitude drops. The values above and below the threshold are incremental and vice versa (amt). They are not simple ons or offs, but have values that are in direct correlation to the velocity. In other words, we have varying amounts of loudness, as opposed to just a quiet and a loud.

With older analogue synthesizers, you do not have that type of velocity control, only a note on or a note off. You have ADSR of the envelopes but not velocity control in terms of how hard a note is pressed.

A very common and extremely versatile use of velocity modulating a destination, is with regards to filter cut-offs. Piano samples are often patched so that velocity controls, not only amplitude, but also filter cut-off, so that the harder a note is struck, the louder it gets and the brighter it gets. When cleverly and subtly programmed, the piano will sound more natural.

Velocity is used for expression, effect and as another modulation tool in the arsenal of a synthesizer’s programmability.

Have fun with it. I do.

These tutorials have been a simple introduction to the deep, yet extremely fun, world of synthesis. To say that we have barely touched the surface would be the understatement of the year.
I plan on continuing these tutorials, either as an open resource, or in the shape of e-books.

However, up unto this point, you have enough information to get you started on basic programming. You will pick up excellent pointers on the way, usually, by accident, and this will instil information and methodology in your minds far stronger than if I had to spell it out for you.

I sincerely hope you have both, enjoyed this little trip with me, and, even more importantly, gained an insight into the wonders of synthesis.

I hope, even more, that you have developed a taste for programming, so that you do not always have to rely on synthesizer presets for your compositions as much as you used to.

Take care and we will meet again.