The modules presented so far – tone generators and filters – can already be used very well and in a variety of ways, they are part of the standard equipment of every synthesizer.
The modules in the following chapter, on the other hand, are more like special tools: wave multipliers, frequency shifters, ring modulators, bucket brigade devices – that sounds more like studying electrical engineering than making music, doesn’t it? Nevertheless, I believe that some of the most exciting modules can be found here. Even if you only want to put together a very small modular system: Take one of the modules described here “on board” and let yourself be surprised!
- Wave shapers are devices that can change the shape of waveforms, sometimes drastically. The waveshapers presented here do this by cutting off or “folding” parts of these waves.
- Bucket Brigade Devices (BBDs) delay signals using a simple circuit that has some interesting side effects. It goes without saying that we also make these side effects musically usable.
- Ring modulators and frequency shifters produce non-harmonic, often “metallic” overtone spectra.
- Frequency dividers add a lower pitched second tone to a tone.
- Among the modules from Doepfer there are other “classic” effects such as analogue and digitally generated reverb, bitcruncher, etc.
The waveshapers described here are all based on the fact that parts of a waveform are cut off or “folded over” (clipping or folding). Of course, this only works for waveforms whose shapes actually change as a result: Square or pulse waves usually remain quite similar to what they were before, even after the upper and lower ends have been cut off or flipped over. However, there are always exceptions due to artifacts.
Clipping and folding of all other waveforms always adds additional harmonics, so they are something of a “counterpart” to filters that remove parts of the sound. A modulation of the Waveshaper brings with it a basically very lively sound, which often moves somewhere between guitar amplifier and digital synthesizer.
Posts on Waveshapers
- A-116 VC Waveform Processor
- A-144 Morphing Controller
- A-167 Analog Comparator / Subtractor / Offset Generator
- A-168-1 PWM Generator
- A-172 Maximum / Minimum Selector / Rectifier
Bucket brigade devices (analog delays)
A bucket brigade device (BBD) takes the voltage present at its input and passes it through a series of analog latches (the “buckets” in the chain) to its output. Technically, the buckets are small capacitors that can be charged and discharged. Picking up and passing on to the next bucket is carried out with a very high frequency and synchronized at all points in the chain. Depending on the clock frequency and the length of the chain, it takes a certain amount of time before the voltage has migrated through the BBD – a delay has been created.
The bandwidth of the delays ranges from a few milliseconds to a few seconds, feedback of the delayed signal back to the input is also possible. This creates various chorus, flanger and echo effects.
The A-148 Dual S&H and A-152 Voltage Addressed Switch modules are something like two “bucket brigade devices in miniature”! A sample & hold module is comparable to a single bucket of a BBD: A voltage applied to the input is stored and is then present at the output of the module until the next voltage “sample”.
Aside from delays with BBD circuits, a few other modules also offer “effects” that are also known from guitar effect pedals, e.g. digitally or electromechanically generated reverb. Nevertheless, integration into a modular system can be worthwhile if the parameters are modulated via the synthesizer’s control voltages (e.g. ADSR, LFO).
The phasers, which are also quite popular as foot pedals, can be found in the chapter about the filters.
Posts on bucket brigade devices, reverb and digital effects
- A-112 VC Sampler / Wavetable Osc.
- A-188-1 BBD Module
- A-189-1 Voltage Controlled Bit Modifier / Bit Cruncher
Ring modulator and frequency shifter
Ring modulators and frequency shifters were used in modular systems very early on: The circuit of a ring modulator is comparatively simple and the very “metallic” sounds that could be achieved with them were soon valued as unusual effects.
Posts on ring modulators and frequency shifters
Excursus: VCAs as sound shapers (amplitude modulation)
When you create interesting sounds with ring modulators and polarizers, you are basically just using the effects of amplifiers and inverters, which are modulated so quickly that they themselves change the input waveform.
But even without inversion you can create very unusual sounds, e.g. with two VCOs and one conventional VCA.
Clearly recognizable: the modulating square-wave signal causes the triangular signal to switch on and off at high frequencies. The result is vaguely reminiscent of ring modulation, but is much less “bell-like” even with VCOs that are strongly detuned to one another, but sounds more like a distortion / waveshaper.
Frequency dividers (sub-oscillators)
Frequency dividers are – after all the “exotic ones” – again quite commonplace devices. Instead of a second oscillator (expensive!), many simple analog synthesizers had a built-in frequency divider (inexpensive!) – this was then often referred to as a “sub-oscillator”. The popular “Octaver” guitar foot pedals are also frequency dividers.
A frequency divider typically creates a square wave signal from almost any input signal. The square-wave signal generated has a frequency of 1 octave below the input signal (1/2 frequency), for example. But there are also other dividers, e.g. further sub-octaves (1/4, 1/8, 1/16 such as with the A-115 or even up to 1/64 with the A-160-1) or any integer divisor (1/3, 1/5, 1/7, etc. like the A-113 or A-163).
The frequency dividers are discussed in detail in the chapter on tone shapers because they are very often used for enriching audio material. But they are also (with the possible exception of the A-115) very well suited for dividing gate signals. Complex rhythmic structures can be generated especially with odd divider ratios (1/3, 1/5 etc.).
Posts on frequency dividers
- A-113 Subharmonic Generator
- A-115 Audio Divider
- A-160-1 Clock/Trigger Divider
- A-160-2 Clock/Trigger Divider II