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 Forum index » DIY Hardware and Software
Hard vs. Soft Sync
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françois



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PostPosted: Thu Mar 20, 2008 3:42 am    Post subject: Hard vs. Soft Sync
Subject description: Anyone could explain ?
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Hello all,

I'm in the process of redrawing a bunch of schematics for various modules (nothing really original, just the usual stuff, just a few enhancements and snippets here and there).

I'm stuck with the VCO core. My starting point is a classic ASM-1 type (integrator with reset) raising sawtooth generator. But I want a sync input. I do understand that you can externally force the comparator to fire at any time, thus resetting the integrator. This is what I understand to be called "hard sync".

Then what is "soft sync", which seemingly has an "intensity" control ? Is it just the same as "hard sync" except for an attenuator (I doubt it is) ? Or (more likely) something more subtle?

I've read plenty of documents trying to explain the difference, many of them with waveform diagrams, but I still can't understand. Most of them insist on things like "harmonic locking" or even "approximate harmonic locking", which adds confusion (to me) and shame (for being dumb).

If anyone would be kind enough to give me an explanation of what happens (I mean at the electronic level) in "hard" and "soft" cases, and why they are different, I would greatly appreciate, and be grateful forever!

thank you,

-- françois
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ian-s



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PostPosted: Thu Mar 20, 2008 5:04 am    Post subject: Reply with quote  Mark this post and the followings unread

You are exactly correct with your definition of hard sync. The term Soft sync is used to describe two different variations which might be the cause of the confusion.

Case 1

With a triangle core VCO, it is possible to have the sync signal reverse the slope of the waveform, so for example if the triangle was ramping up and at 70% of it's max level when the sync triggers, it will start ramping down from 70%.
The discontinuities are not as sharp as with hard sync, creating a much more subtle effect but it still sounds similar to hard sync. I don't think it can be easily done on a saw core VCO.

Case 2

There may be variations on this, but the one I am familiar with 'windows' a regular hard sync input so that the reset will only occur if the level of the slaved oscillator is close (variably) to it's peak value. This is also called weak sync by Roland on the 100M. I find the effect not as useful as with case 1, it sounds like the sync is not working properly Laughing
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Clack



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PostPosted: Thu Mar 20, 2008 6:02 am    Post subject: Reply with quote  Mark this post and the followings unread

so is the reason we have soft sync is so that you don't get the harmonics of a waveform that is being cut through resets? or are they just similar things done in different ways?
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Dan Lavin



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PostPosted: Thu Mar 20, 2008 6:27 am    Post subject: Reply with quote  Mark this post and the followings unread

Mr Clack and françois,

I think soft/hard sync is just personal preference. The soft sync is not as harsh but gives a similar effect to hard sync. My first exposure to sync was Jan Hammer with his Oberheim SEM's and I just fell in love with it...but I'm a rock guy and therefore lover of the the non-subtle.

Guys, I'd suggest you do a google search for sound samples or find an analog VST synth that can do both syncs and audition them. We can describe in both technical and non-technical terms, but in the end it's just words. Your ears are what you need to truly evaluate.
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etaoin



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PostPosted: Thu Mar 20, 2008 6:53 am    Post subject: Reply with quote  Mark this post and the followings unread

And to make matters even more confusing; the CEM3340 can do two types of hard sync, depending on whether it is synced by positive or negative pulses... and it's a different hardsync than the one described above (in fact, it's more like the case 1 soft sync...)


cem3340_hardsync.jpg
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CEM3340 hard sync
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frijitz



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PostPosted: Thu Mar 20, 2008 8:51 am    Post subject: Reply with quote  Mark this post and the followings unread

Excellent explanation by g2ian.

My TRI VCO has what I call "kick" sync. The sync signal is a narrow pulse that forces the TRI to ramp down. Eventually the waveform locks into a steady pattern, i.e., becomes hard synced, but there is a transient time during which the sync pulses gradually kick the oscillator towards the steady waveform. I guess this is similar to the Case 1 soft sync described above and to one of the Curtis sync modes. It gives the folded triangle waves as shown above.
http://home.comcast.net/~ijfritz/sy_cir4.htm

Very Happy

Ian
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françois



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PostPosted: Thu Mar 20, 2008 9:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmmm... so that was (only?) it ? Thank you all, now things are a lot more clear in my mind.

Obviously I can't have soft sync with a sawtooth oscillator, not even with the triangle wave obtained by rectifying the sawtooth. A triangle VCO is required. But I don't like too much triangle VCOs (don't ask me why, probably some genetic background).

So I will stick with hard sync only, which also happens to be considerably simpler to implement.

And I do agree that ears are the ultimate judge. But when you're actually designing the circuit, a bit of electronic knowledge is indeed helpful...

-- françois
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Grizzle



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PostPosted: Thu Mar 20, 2008 1:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

I don't much about the technical end of things but....

On the A-111 the Soft Sync locks the A111 to a harmonically related frequency of whatever you're using as a master oscillator. It's a very quick way to tune 2 oscillators together. You can use it to force the A-111 osc into a unison, octave fifth relationship with the master oscillator... It's a handy function.

Hard Sync has already been explained.

Cheers

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ian-s



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PostPosted: Thu Mar 20, 2008 2:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

Grizzle wrote:
On the A-111 the Soft Sync locks the A111 to a harmonically related frequency of whatever you're using as a master oscillator.


Looks like the A-111 uses the CEM3340. The pdf manual is an excellent source of confusion. From what I can see, the A-111 hard sync is soft sync, and the A-111 soft sync is, um... actually I have no idea what it is.
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toppobrillo



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PostPosted: Thu Mar 20, 2008 3:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

the reason i got into the thru-zero project to begin with was that i was trying to add a proper sync to a triangle-core vco circuit.

simply discharging the integrator in one direction in the tri-core is a sync alright, but it doesn't 'sweep' at all like the classic Syncs of Old- kind of jumps in octaves, which is cool but i was after the more familiar sound.

after some pretty much unsuccessful [slightly, but too complex parts-wise. i have come up with a new idea which i have yet to try] attempts at 'resetting' the integrator in a bipolar fashion, according to what direction the core is headed, i checked out the CEM data sheet, i was convinced the proper way would just be to reverse the direction of integration... around that time was when the TZ stuff was goin on and so then i decided to work in that direction.

so i built up the digital portion of the 129 and added a 'reversing' sync input that does just that. it sounds alot like what i was after, but like ian's 'kick' sync he talks about [if i understand it right] it takes a sec to lock on once initiated, and a great change in the master oscillator's pitch will throw it off again- so you often get a little bit of a phasing sound before it locks.

so it's kind of soft i guess, but sounds hard. huh?

also, don't forget about "phase lock" ala buchla 259, it's pretty subtle.
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Scott Stites
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PostPosted: Fri Mar 21, 2008 7:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

A long while back I got interested in soft sync; though I don't think I actually got true soft sync, I think I got something similar to what Grizzle is describing.

The idea came out of some Clavia manual I used to have in PDF form (wish I could find it again); thing is, I rigged it up again last spring and got the most amazing effects out of it - I'll see if I can dig up the samples again, if they still exist.

It requires a VCO that already has a hard sync function. What you do is route the output of the slave oscillator to a comparator, and you route the triangle wave of the master oscillator to the other input of the comparator. You route the output of the comparator to the hard sync input of the slave.

Then you rig it so that when the master and slave are at the same frequency, no sync pulse is generated. Once there is a difference in frequency (positive or minus), a sync pulse is generated to sync the slave. The truly great stuff came when modulating one of the oscillators, but off-hand I can't remember which I modulated - I'm thinking it was the slave. Anyway, instead of a smooth transistion in frequency, the oscillator would step, and with sine wave modulation it sounded just like an arpeggiator while locking to the different harmonics. There were some other cool tonal things can could be done, too, by manipulating things.

Oh, dang, I wrote it all up a looonnngg time ago! Sound samples I did last spring were much better, IIRC. I think I changed some things around, but there are diagrams, etc. of the general concept here on my old site:

http://mypeoplepc.com/members/scottnoanh/slsdiy/id22.html

Cheerios,
Scott

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françois



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PostPosted: Sat Mar 22, 2008 4:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello,

Scott's idea of soft sync is really interesting. I'm currently tweaking a similar idea to have soft sync on a sawtooth-generated triangle wave... It looks unfeasible at first, and it is if the triangle is derived from full-wave rectification of the sawtooth wave. But there are other ways to generate a triangle from a sawtooth, and then it might be possible. I shall let you know if I come to something working (that does not mean it would be worth the hassle, e.g. if the parts count is prohibitive).

A look at the CEM3340 datasheet is not very enlightening, there is only a block diagram, and nothing about the internal structure. Of course, I don't know how many transistors there are on this chip, but surely enough to prevent a component-level diagram. So bad.

BTW, I'm also writing a memo about the various waveshapes and effects that can be derived from a sawtooth wave. Most of them are classic, but others are more interesting. This memo is intended for my own use (to avoid having working notes scattered on a bunch of post-its) but I shall post it here if I think it might be of public interest.

-- françois
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PostPosted: Mon Mar 24, 2008 10:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Here's that sample I was thinking about. IIRC, I was modulating the slave oscillator with an LFO. Both oscillators were controlled by my TH keyboard, with the master set at a higher frequency (the freq relationship didn't require the master to be at a lower frequency than the slave). At least that's how I remember it Very Happy

So, it's both VCOs, mixed through my triple SVVCF module, and I'm assuming a VCA. The arpeggiation is just an artifact of my "soft sync" circuit.

There was another recording I made of it that had some chaotic component to it that I'd like Ian to have heard, but I can't seem to locate it. It had a very exotic sound as it sort of breifly danced amongst the harmonics.

Cheerio,
Scott


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funkyfarm



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PostPosted: Tue Mar 25, 2008 9:30 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Then what is "soft sync", which seemingly has an "intensity" control ? Is it just the same as "hard sync" except for an attenuator (I doubt it is) ? Or (more likely) something more subtle?


http://www.oakleysound.com/vco.htm

Oakley Modular Systems has a sync input and one pot. Wink
I guess it's : fully cw for Hard sync, fully ccw for Soft sync, and in between...well, it syncs in between.

All positions are really useful.

Does anyone have one to tell about ?

At least, I'd realy like to add soft/hard input on my SH-101 (CEM3340 based)

Here's the schems for positive/negative/hard/soft sync around 3340 :

http://www.digisound80.co.uk/digisound/modules/80-2/construction/80-2&3_ETI.pdf

http://www.digisound80.co.uk/digisound/modules/80-2/construction/80-2.pdf
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Funky40



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PostPosted: Mon Mar 31, 2008 4:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

funkyfarm wrote:
http://www.oakleysound.com/vco.htm

Oakley Modular Systems has a sync input and one pot. Wink
I guess it's : fully cw for Hard sync, fully ccw for Soft sync, and in between...well, it syncs in between.

All positions are really useful.

Does anyone have one to tell about ?



I have anyware-Instruments (DIY ) VCOs ( Minimoogclones with common parts)
they have also that Pot to turn from soft to hardsync.
there must be a Demo
http://www.modularsynth.net/topic-505.html
seems to be allways around 2-third where it is most useful when i remember right.
I just experimented 2-3 times with sync
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