Circle Tutorial 7 - Creating Sample And Hold Synth Effects

What is Covered?
An intermediate level tutorial on using the classic sample and hold effect.
Introduces the design of sounds using the filter in self oscillation.


You may not of heard of the term 'sample and hold' before but it is very likely you have heard this synth effect in action. If you have heard the classic track 'Rez' by Underworld then you will certainly be familiar with what these fx sound like. They have also been used in countless other electronic tracks.

A sample and hold LFO is simply a random, stepped waveform that when used to modulate the pitch of cut off frequency in a patch, will produce a very distinctive sound. Although Circle doesn't strictly have sample and hold type waveforms available in its LFO sections, there are ways to create this classic effect, lets take a look at how its done.

Step 1 - Choosing the oscillators

Circle has already been initialised by hitting the 'new' button at the top of Circles interface and is now ready for programming.

The initialised patch

When creating a sample and hold effect it's not hugely important what oscillators we choose as the core of the effect is created by a self oscillating filter (don't worry this is explained in later steps). You can pretty much apply this effect to any type of sound but in this case I went with a few different oscillators to provide a sonically rich foundation for the patch.

I have used two saw-tooth oscillators here, one of them de-tuned by 7 semi-tones for extra thickness and i have also added a mixed wavetable oscillator and a small amount of the special feedback oscillator for even more flavour. These are all then mixed in Circle's mixer section.

The initialised patch

The initialised patch

The various raw oscillators.

Step 2 - The self oscillating filter

To get this effect to work correctly we need to use an extra sound source, a self oscillating resonant filter. When some analogue filters (or in this case analogue modelled filters) are used with extremely high resonance settings, they begin to self oscillate, becoming their own sound source.

Self oscillating filter

This essentially means you don't need any actual oscillators at all. They could be switched off entirely and they filter would still generate sound in this state. The audio clip below demonstrates what a self oscillating filter in isolation sounds like.

Self oscillating filter in isolation.

Step 3 - Creating the sample and hold effect.

With our filter self oscillating and all our sound sources in place and switched on, we are ready to start creating the sample and hold effect. As I mentioned at the start of the tutorial Circle doesn't actually have a traditional random LFO wave form we can use, but instead we can utilise the built in step sequencers to automate the filter and create the effect we are after.

Once the sequencer module is activated you can try experimenting with the 'random' function. This will give you a set of random values pre programmed and the result is very similar to that of a random LFO. Now attach the sequencer to a spare frequency mod slot in the filter section. On turning down the cut off frequency you should start to hear the effect.

The random sequencer

The filter modulation

You can now adjust the individual steps within the sequencer to create your perfect pattern of modulation. if you intend to use the sound in the mix it's certainly worth auditioning the sound with other instruments at this point to male sure everything gels.

Other settings in the sequencer to be aware of are the sync and re-trigger buttons. The sync button will simply synchronise things to your hosts bpm ensuring everything is perfectly in time. The re-trigger function will restart the sequencers pattern every time the sound is triggered via midi. This can be very useful when using the sound in a sequence or loop.

The random sequencer effect.

Step 4 - Further modulations.

To add some variation to the sequencers movement I have used a further LFO to modulate the filter cut of frequency. This is a simple sine wave based LFO and is also synced, so that it will move in time with the sequncers pattern.

Filter LFO

Final filter settings

Further filter modulation.

Step 5 - Adding effects

So our sample and hold effects patch is pretty much completed but for a finishing touch lets add some effects from Circle's excellent built in multi fx processor.

I used a simple chorus pre-set mixed at a pretty low level here to add some width to the sound, followed by a ping-pong stereo delay effect. The low end was filtered out in the delay section to keep things as clean as possible. The combination of the two effects really open the patch up and make it that little bit more interesting to listen to.

Chorus and delay effects are added.

Again this is a relatively simple patch with only a few modulation routings but you can see that by using the sequencer as a modulation source that really interesting and usable patches can be developed..

Final patch overview.

Final patch with effects.

Download Tutorial 7 Files

Tutorial 7: Creating Sample And Hold Synth Effects
Download the tutorial in plain text format, the associated audio files and the completed Circle sound/patch.