Okay - I have cracked this, and to be honest, it only makes me love the charm of the ARP 2600 design even more - I like these little things which work differently amongst synths, it introduces unexpectedness if you make too many assumptions … thus the reason to explore and begin to understand/utilise/master etc
So firstly, I’m happy to report all is well with the Blue B … this is a 2600 thing and I think it merits an exploration on your part if you’re an owner (especially recently) of any variant
The important takeaway, for anyone not wishing to delve a bit deeper (useful illustrative patch shown below), is that it’s important to discard the idea that gates are a binary thing … on and off … start and stop … as this is not the full picture with the 2600
This explains my confusion when I was perceiving reduced VCA output even though I was successfully ‘triggering’ both envelopes (reduced, wrt comparing internal ‘gating’ in contrast with certain external gear, pretty much everything except the A4 … kudos due to Elektron here for delivering the goods)
The other thing I’m annoyed I forgot about, but had never confronted in practice (best way to learn/remember), is that the 2600 AR (or maybe best though of as an AHD) is akin to a slew limiter (or a second onboard lag processor, but with independent slew rates for onset{A}/end{R}) so in this case the H(hold/‘sustain’) level is in fact the gate voltage level … so the ‘gate’ in this case is not merely acting as a binary/timed switch but it acts as the terminal voltage level at the end of the attack slew
What I was witnessing in my previous tests was that the relatively ‘reduced’ volume was determined by the lower gate strength of the devices used (with the sole exception of the A4)
All the goodies you can throw at the ‘gate’ within the 2600 deliver a nice healthy 10v as does the A4, but the advertised ‘10v’ gate from the Korg SQ-64 (although seemingly pumping out 11v as per my meter) was clearly not on spec - same for SQ1, but that is apparently set at 8v, so its effect on the perceived volume shouldn’t have been a surprise had I not thought of a gate as being a binary switch that works when it reaches a threshold voltage (Microfreak/Crave/Doepfer Dark Energy don’t deliver any better than the SQ1 or SQ64, but it may only be the SQ64 that indeed promises 10v, I haven’t checked the respective specs)
Incidentally, when using the A4 (which permits setting a gate level of your preference up to 10v, I noted that there was some ‘triggering’ when the output was as low as 3v (iirc, that’s what’s needed to activate the AR/slewer) and if my memory serves me the gate (but not yet trig) voltage for the ADSR is North of that (5-6v) but well short of 10v … and the test patch below beautifully illustrates the interconnectedness and what is happening with the 2600’s envelopes depending on gate levels
In this examination it hasn’t seemingly been necessary to examine gate ‘profile/shape’ but it would be unwise to discount that this could play a factor given the other nuances of the design
In contemplating how best to present this, I decided the best way to learn is NOT to read, but to TRY ! so I came up with the simplest method that should apply to all variants including the og, so with that in mind B2600 owners need to put the two envs in the mid(1x) time factor state. Repeat is off, voice mode mono and trig mode was left on single for simplicity)
The rest of the patch is a simple square from VCO1 sent through an open filter, the filter feeds the VCA which is opened by the AR, VCA to Mixer - see image - everything is in place, note that I haven’t ringed the VCO1 freq (forgot), that’s an important level, it’s difficult to quantify with the log value, I find it much more useful to vary pitch than volume when auditioning modulators. Keytracking is on and there’s no Midi but despite the initial osc freq being in the 5k region, the actual frequency is offset internally, just be sure that what you hear is about 440Hz (with no(i.e. zeroed FM) ADSR modulation), that is to allow headroom to hear the two stages of pitch modulation the patch illustrates … it’ll make sense when trying this out (it’s just much easier to perceive volume changes in modest frequencies and freq changes too)
For comparison between internal and ‘external’ (i.e. voltage from an alternative source) it is simplest to use the [S/H Clock] input to trigger the envelopes (although we’ll be inserting here and breaking the normal from the 10v clock)
A recap, when the S/H switch is down a 10v signal will activate both the AR/ADSR identically to pressing the Manual button, by using that input we have a metric for gate strength now, so we can vary the incoming gate level triggering (or not) the envelopes … also note, the Trig in although adjacent to the AR actually relates to the ADSR only, the Trig in is nothing to do with the AR, and as you’ll see, there’s two ways to activate the ADSR depending on gate voltage, so by varying the gate strength we actually have three envelope permutations !! corresponding to let’s say circa 3v 6v 9v
3v will trigger the AR slew and as we’re using this for the VCA it’s relatively quiet
6v will trigger the gate of the ADSR (but not the Attack stage yet) … so there’s a secondary slew type envelope using the DSR, where D and R are akin to A and R of an AHD, and in this case, H is modulating the freshly opened gate which targets VCO1 pitch, so the pitch is raised now (start with zeroed D & R and lift them a little to see the slewing of pitch)
9v will properly trigger the ADSR, i.e. it triggers the Trig in now, so it actually utilises the Attack phase of the ADSR and with the attack phase jumping to 10v, you get an even higher pitch trace
(PS it’s not exactly 9v or 6v btw, just making it read simple with 3/6/9 … it’s probably 3/5/7 on the B2600 … og ARPs may have different sensitivity thresholds)
So to explore the effect of Gate level (and keeping it all in house for the 2600) we’ll use the voltage processor to offer up an attenuate-able 10v signal that we’ll ‘gate’ on off with the Electronic switch - set the Sample and Hold Rate around the 10% or circa 1second)
That’s what we feed to the Gate input, and we can attenuate the inverted -10v (i.e. 10v) by varying the slider (red arrow) left to right … left is attenuated, right is ‘open’
So by varying the attenuator on the net 10v (a tad less coming out of the B2600) signal you can get 4 envelope states
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Both Off
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AR On (low volume)
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AR On (mid volume) + DSR (i.e. an untrigged gated ADSR acting like our AR/slew as the Decay stage acts like an attack stage by going from 0v to sustain level)
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AR On (High Volume) + ADSR (i.e. a trigged & gated ADSR, so the Decay stage is Max to Sustain level (for a long enough gate as per our controlled experiment) )
Hopefully experimenting with the patch below will help consolidate your knowledge of how the 2600 envelopes are activated - that should make using the independent gate inputs and the ADSR Trig input a bit more intuitive going forward
If you can get a gate of e.g. 8v say, then it will ‘fully’ trigger the two envelopes, but you just won’t get the same oomph from the VCA as the AR envelope is slewing a ‘lower’ voltage of 8v as opposed to the 10v you get internally from the S/H clock (or Manual, or LFOs(untracked osc) etc etc
Thus my original perceived (i.e. non) issue … so lower gate voltages can work, but they don’t necessarily equate to what’s possible with the 10v internally, depending on chosen application - it’s probably not too significant with the AR as VCA … I was just puzzled as to the why it was quieter
Anyway, hope this little patch helps, it helped me to simplify it like this … the 2600 is an amazing utility device as well as incredible sounding
Start with this config (especially ADSR levels) and have fun varying the VP slider to see the 4 phases or activation
PS the original manual is incredibly helpful, but I’m not sure it elucidated the initial way the ADSR can be ‘activated’ (sans A i.e. sans Trig)
Sorry for loooong post !
