Robin Whittle 1 June 1999
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Tony Clark ( clark@andrews.edu, http://www.andrews.edu/~clark ) wrote something that is often said in respect of the TB-303: that it does not do anything unique. > I think that the whole point is that other equipment will rule the > dancefloor just as well as the 303. A good "anything" track will get > everyone dancing. The whole discussion of "it's easier to use", "has a > better sequencer", "has a unique sound" is stupid simply because there > are an infinite number of ways to accomplish the same thing that the > little silver box does. There are a number of things that only the TB-303 can do - which cannot be done with a modular synth using standard modules. Ignoring for a moment the exact sonic nature of the filter, which may be unique, I want to concentrate on the accent system. I really need a block diagram for this. There are two envelope generators in the TB-303. I have named them: The Volume Envelope Generator (VEG) Sharp attack, exponential decay, fixed decay and rather long time. (In the Devil Fish it can be altered between very short, normal and infinite sustain.) Drives the VCA and does nothing else. The Main Envelope Generator (MEG) This primarily controls the filter frequency. It too has sharp attack and exponential decay. MEG has two possible times. On normal notes, there is a variable time, controlled by the Decay pot. On accented notes, this is shorted out and MEG runs to the relatively short time which is the same as when the Decay pot is fully anti-clockwise. (The Devil Fish provides independent control of MEG time for both normal and accented notes.) For both normal and accented notes, the MEG affects the filter frequency via the Env Mod pot. However the circuitry does not allow this effect to be turned down to zero even when the pot is fully anti-clockwise. (The Devil Fish allows this and extends the amount of Env Mod when the pot is fully clockwise.) On an accented note, the MEG performs two other functions. In both cases the MEG voltage goes through a switch (which is only on during accented notes) and then through the Accent pot: 1 - It adds to the control current of the VCA. (Via an RC network of a 47k and a 0.033uF to soften the attack a little.) This is the primary reason why accented notes are louder. Note that in a TB-303, the MEG time is fixed and short for accented notes. 2 - Via an "Accent Sweep Circuit" it adds to the filter control current. Basically this raises the filter frequency on accented notes, to a degree controlled by the Accent pot. All the above is unique to the TB-303. It would be impossible to implement such things on any synthesizer I know of - except by building special additional circuitry. The real fun is in the "Accent Sweep Circuit" (my name). This involves a diode and a 47k resistor in series driving the ACW (anti-clockwise) end of a 100k pot, and a 1uF capacitor (to ground) hanging off the CW end. The wiper of the pot goes via a 100k mixing resistor to one of the two summing nodes for filter frequency. If the pot is ACW, then the filter is driven largely with the output of the MEG, but the capacitor must always drain via the 100k, since it gets some charge and this is via the diode. This means that the filter gets a sudden hit of control current to increase its frequency - largely a direct copy of the output of the MEG. (It is basically 100/147 of the MEG voltage minus the capacitor voltage. The capacitor voltage does not change a lot when the pot is ACW, since most of the current goes out via the wiper of the pot rather than through the pot to the cap.) If the pot is fully CW, then the pulse of voltage driving the filter is smoothed by coming from the 1uF cap as it is charged via the diode and 147k of resistance. !!! This pot is the second section of the Resonance pot. !!! What this means with a single accented note: The filter goes "Wow." It rises and falls in a quick, smooth curve. ***** *** ***** ** ***** * ***** * ****** * ********* * ******************* This is rather unique - is is not the angular response you would get with a ADSR envelope generator. The real fun happens when you have multiple accented notes in quick succession. Since the capacitor has not discharged fully from the one before, the second and subsequent response curves go *higher*: ***** ***** ** *** *** **** ** ** **** * ***** * **** * *** ***** * **** ** ***** * * **** * * * Human listeners - and probably a few furry quadrupeds - interpret this output of increasingly high pitched audio signals as sounding like the cry of a living creature becoming increasingly distressed, apparently in response to quickly repeated bursts of stimulus. Whole essays could develop from this, in terms of how a few simple passive components in the TB-303 mimic the distress cry of a living, sentient creature. This is especially important in the context of the effect happening more as the filter's resonance is increased. There could be speculation as to how this audio response to distress evolved, both in nature and in the TB-303. From there, it is relatively simple to postulate that humans and other intelligent forms of life would evolve to develop an analagous emotional response when hearing such sounds. All these are left as exercises for the reader. Meanwhile, instinctually, many people are putting the TB-303 to use and millions more are dancing as if possessed. A few people are staring at computer screens and writing that the TB-303 has no unique characteristics - and quite a few more beleive them. It may well be that the TB-303 has become a fashion statement and so has become over-rated. However there is a very real basis for its popularity amongst musicians and listeners. It has a fluidity, uniqueness and a somewhat animal quality which is lacking in most other electronic instruments. The bubbly little sequencer helps. The accents and to a lesser extent the slides have no parallel in other gear. Like any other form of music which becomes popular, there is an increasing number of empty-heads doing it and a great deal of reductionism and "monkey-see monkey-do" generic product - leading to boredom and saturation. We have had a few years of that in techno, a few decades in rock and a few centuries in earlier forms of western music. To experience a truly inspired, minimal, energetic, abstract TB-303 acid romp, check out Hardfloor's 1992 "Aceperience 1". I think that acid music has a lot to do with these curves of filter response rising with repeated accents. Reverb and slowing the thing down (via a playing it on a sampler at a lower pitch) probably has quite a bit to do with it too. However there are many other relevant musical elements - most of which resist scientific analysis. - RobinReturn to the main Devil Fish page.