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Design considerations for the Syntiac synthesizer

This page contains motivations for the design methods we use in the Syntiac synthesizer. These can be different from you own experiences. This is work in progress and some statements and details can change when we proceed with building of the modules.

Level controls on outputs and not on the inputs

Because there are many more inputs as outputs in a modular synthesizer, we can save on the amount of pots, providing level control on the outputs instead of the more common way on the inputs. This saves about 50% of the controls which makes the synthesizer more compact and cheaper. Only when a output is connect to more as one input a problem can arise. This is solved in two ways in the Syntiac. There are separate attunuation controls available with 1 input and 2 or more outputs (each with its own level control). Secondly there are a large amount of LFOs and ADSRs planned so it is more unlikely that they must be shared between modules. Ofcourse all these LFOs cost money to, but also give extra functionality and LFOs are cheap to build. In the Syntiac there are also extra VCAs available which make it possible to modulate the output level with a control voltage (for example with a LFO).

Patch cables

Now following a couple of considerations for choosing the connector and patch cable type for the Syntiac synthesizer. Each type has its own benefits and drawbacks

Banana plugs

Very solid connections, almost indestructable. The cables can be stacked on top of each other, so a single output per module is enough. Banana plugs provide a single connection only, so connections are not shielded. Which can be a problem for lowlevel signals. Most signals in the Syntiac are +/-10 Volt which have a high tolerance to noise. The cables and sockets are available in many colors.

Mini jack

Cheap and providing both signal and shielding. A switch between the signal tip and a second internal connection can be interrupted by inserting the plug, which makes pre-patching easy. Self made cables are mostly not of the quality expected (plugs become lose or the cable protection breaks).

Normal jack

Rock solid, expensive and HUGE. These connectors take a lot of frontpanel space, which makes them unsuitable for a modular synthesizer. No problem for the connection to mixer equipment though.

Alternative Envelope settings idea

This is an idea I want to try out some time. It is a alternative to the common used ADSR envelope generator. The ADSR envelope generator is almost a default item on a synthesizer. Some use simpler systems like ADR or AD, others use a more complex one like ADHDSR (Attack Decay1 Hold Decay2 Sustain Release). Envelopes are used to control filters, oscillators and amplitude modulators. In a decent synth at least 2 are present to modulate filter and amplitude independed of each other. My idea is to merge the filter envelope with the filter settings itself. The combined set of settings will be:
StartCutoff, AttackRate, TopCutoff, DecayRate, SustainCutoff, ReleaseRate, FinalCutoff. Because the levels are all absolute the envelope can emulate both positive and negative running ADSRs (which by the way not all synths provide). The Rate settings control a exponential curve, so the elapsed times are independed on the level settings.


Digital ADSR+filter formulas (internal use Peter)

VCF: startCutOffLevel, attackRate, topCutOffLevel, decayRate, sustainCutOffLevel, ReleaseRate, endCutOffLevel.
LFO: beginSpeed, endSpeed, SpeedChangeRate, beginAmpl, endAmpl, AmplChangeRate.

CutOff = startLevel
CutOff = CutOff + (((topLevel - CutOff) * AttackRate) / Factor)
CutOff = CutOff + (((sustainLevel - CutOff) * DecayRate) / Factor)
CutOff = CutOff + (((endLevel - CutOff) * ReleaseRate) / Factor)
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