Specs of a Eurorack Clock Signal

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yentzee
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Specs of a Eurorack Clock Signal

Post by yentzee » Wed Sep 09, 2020 12:10 am

Hi,
Could anyone tell me the ecact specifications of an Eurorack Clock signal?
Pulses per quarter, pulselength, pulse current
Thanks a lot

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Re: Specs of a Eurorack Clock Signal

Post by nigel » Wed Sep 09, 2020 12:49 am

In a modular system, a clock is just an on/off signal that makes something happen, maybe stepping a sequencer, or starting an envelope, or flipping a switch. There's no such thing as "pulses per quarter" (although if you're converting a MIDI clock for example, you can probably select how often it outputs a clock signal). On and Off are not very well defined - a clock output on a module will generally switch between 0V and something over 5V, although that can vary. A clock input on a module may need a sharp on/off signal, or it may just take any voltage over some threshold as "On". Some modules will behave differently while the clock stays On (for example, many envelope generators), while some will just respond to the change from Off to On. Finally, like all (?) modular signals, it is a voltage, not a current, as module inputs are high impedence.

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Re: Specs of a Eurorack Clock Signal

Post by yentzee » Wed Sep 09, 2020 1:49 pm

I know that it is a pulsewave (on / off)
How is the pulsewidth specified. If I am having a ration of 50% 50% on 50% off would that be sufficient or does it have to be 5% on and 95 % off?
If your are saying there is no pulses per quarter specified how would I know / extract the information what is a bar or a quarter note etc. Lots of modules do offer the abillity to set 16th 8th etc but obviously you can just define something as an 8th 16th or anything else if you have a form of reference (like a 16th of what and for that you need to know that xxx ticks are equal to one bar or similar) I might be wrong and just missing the point, please dont get me wrong. I am not a native speaker and not telling but asking and trying to formulate my thoughts.

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Re: Specs of a Eurorack Clock Signal

Post by nrrrd » Wed Sep 09, 2020 3:00 pm

There really isn't a specification for a Eurorack Clock Signal. It will be a pulsewave of some description. In essence, it doesn't matter what the clock module outputs, what matters is how the module receiving the clock signal interprets it.

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col
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Re: Specs of a Eurorack Clock Signal

Post by col » Wed Sep 09, 2020 4:13 pm

The only Eurorack spec you will really find is what Dieter laid out in the Doepfer FAQ.

http://www.doepfer.de/home_d_2019.htm

" Sync specification

The SYNC standard was introduced in the eigthies by Roland for synchronization of sequencers, drum machines, arpeggiators and similiar devices. The SYNC standard uses the signals clock (or tempo) and start/stop (or run/stop). The signals are TTL compatible. This means the low state is 0V, the high state is about +5V. The clock signal defines the speed of the sequence or drum pattern. The start/stop signal defines if the sequence is running (start/stop = 0V -> stop, start/stop = +5V -> running). The frequency of the clock signal is defined as 24ppq (24 pulses per quarter note) which is the same as the Midi clock specification which is 96 ppm (96 pulses per measure). Consequently the Midi clock can converted directly into SYNC clock by suitable devices (e.g. MSY2). Pay attention that some manufacturers used other clock standards. Korg used e.g. 48ppq which means that the SYNC clock (or Midi clock) has to be doubled which cannot be realized very easily. Slower clocks (e.g. 4 ppq or 2ppq) can be derived from the SYNC clock simply by frequency division. E.g. the MSY2 has some switches to adjust the clock dividing factor from 1:1 (96ppm=24ppq) to 1:16 (6ppm=1.5ppq)."

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Re: Specs of a Eurorack Clock Signal

Post by Hutenberger » Sat Sep 12, 2020 3:31 am

Thank you for posting the SYNC spec! This gives good information about timing/speed.

But thinking more about that, what about the slope of a clock signal? Should for example a slow sinewave also be recognized as a clock in a module?

Sine accepted = module compares input voltage to a fixed voltage, meaning it rectifiers the wave internally

Sine not accepted = module converts rising edges to a short pulse internally (e. g. capacitor in series as a high pass filter) and detects that as a clock. This will not recognize a slow sinewave as a clock, no matter of its voltage range.

What is your experience with the modules you have, how do they handle it and - most importantly - what do you think is more usable?
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Re: Specs of a Eurorack Clock Signal

Post by KSS » Sat Sep 12, 2020 5:08 am

Your first example is not rectification. It will clean up the sine to a rising -or falling- "edge" to the quality of your comparator circuit. It's common and preferred. But its output is not a pulse. It's an "edge". One indicative of a "level" you've chosen. Presenting a new level -that you've also chosen, or accepted- to the rest of your circuit, which starts at the edge.

Your second example puts more 'rules' around the input. More importantly as a designer, it takes you out of the decision, so to speak. You're now dependent on what OTHER modules and their designers do or don't do. That's never a good choice if you're after robust module design. If you're looking for variable input it might be okay. But definitely not preferable in the vast majority of cases.

You might still include the second example internal to your module if you need a pulse rather than a level. Converting a level into a pulse is not a given and depends on what you're needing to do with the input.

Put another way, inputs are not always about strict timing. Even though those in this thread could be assumed to be so. Gates and triggers are both timing related inputs. but they do not convey the same information. Sometimes one or the other is enough. Other times you need both.

And it's really important to be clear about whether you're talking about-dealing with rising or falling edges. Either-or-both are used. Make sure you know which is which and what you need or want to do with each.
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Re: Specs of a Eurorack Clock Signal

Post by EATyourGUITAR » Sat Sep 12, 2020 5:56 am

I don't have numbers on this but I will say that there is a sweet spot in eurorack for rise time to have the maximum compatibility with other manufacturers. not too slow not too fast. just right. some modules have comparators at the inputs. some modules don't. some modules have schmitt trigger inputs with hysteresis. some modules don't. a sine LFO into a linear CMOS input on a digital IC is going to suck a lot of power and make a lot of heat. it is rare but it could even cause a module to break after 1 hour of over heating. some modules have AC coupling on the gate for a gate to trigger. very fast rise time through a high pass filter makes a spike that can damage a 5v circuit maybe. in some designs, a very fast rise time will be ignored. eurorack expects cheap low frequency gates never above 20KHz. at that frequency it looks more like a trapezoid. maybe you can use that to derive your hard limit for fast rise time. or go to 30KHz and spec %10 of your duty cycle as rising edge. anything over that would be less compatible with eurorack.
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Re: Specs of a Eurorack Clock Signal

Post by KSS » Sat Sep 12, 2020 7:32 am

EATyourGUITAR wrote:
Sat Sep 12, 2020 5:56 am
there is a sweet spot in eurorack for rise time to have the maximum compatibility with other manufacturers. not too slow not too fast. just right.
I think those are called Goldiclocks.
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Re: Specs of a Eurorack Clock Signal

Post by nigel » Sat Sep 12, 2020 8:25 am

KSS wrote:
Sat Sep 12, 2020 7:32 am
EATyourGUITAR wrote:
Sat Sep 12, 2020 5:56 am
there is a sweet spot in eurorack for rise time to have the maximum compatibility with other manufacturers. not too slow not too fast. just right.
I think those are called Goldiclocks.
Ooof.

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Re: Specs of a Eurorack Clock Signal

Post by pugix » Sat Sep 12, 2020 8:36 am

EATyourGUITAR wrote:
Sat Sep 12, 2020 5:56 am
some modules have comparators at the inputs. some modules don't. some modules have schmitt trigger inputs with hysteresis. some modules don't.
I recently modified the comparators in my Bastl Tromsø modules to add some hysteresis, which fixed a problem I was seeing when gating another module with it.

https://pugix.com/synth/bastl-tromso-improvement/
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