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Technical discussion of DSI synths and their DCO pop

PostPosted: Sun Jul 05, 2009 11:37 am
by Jabberwalky
http://www.electro-music.com/forum/view ... torder=asc

Pretty interesting read. I actually do notice the clicks they mention in the thread. Has anyone here noticed this?

Re: Technical discussion of DSI MEK and it's DCO pop

PostPosted: Sun Jul 05, 2009 3:31 pm
by nuketifromorbit
Jabberwalky wrote:http://www.electro-music.com/forum/viewtopic.php?t=32628&postorder=asc

Pretty interesting read. I actually do notice the clicks they mention in the thread. Has anyone here noticed this?


Last time I stopped by tallowater's place to pick up an ER1 I asked about this very same issue since his mek was out in the open. He seemed to agree that it occurs. I've always considered an evolver, but this issue makes me a bit leery.

Re: Technical discussion of DSI MEK and it's DCO pop

PostPosted: Sun Jul 05, 2009 4:58 pm
by cornutt
Urosh's analysis on that thread was an interesting bit of reading. I'll have to go do some more investigating re his statement about the Juno-106 (and presumably the 60 too) restarting the DCOs at note on -- I haven't picked up on this in my studies of the schematics, but it could be true. I'll have to try to devise a test to see if I can see that.

At least in regard to the 106, Urosh's statement about the DCO having a constant ramp rate is incorrect. The 106 DCO varies the ramp rate according to the frequency, just as a VCO does. The difference is that in the DCO, the ramp rate doesn't determine the frequency. The main reason the 106 does it this way is so the output level of the DCO will be constant; if you use a constant ramp rate, the output level will decrease with increasing frequency.

If the Evolver DCOs do in fact use a constant ramp rate, then there must be something to compensate the output level. If you put a VCA on the output and fed the frequency CV to it, that would do the job. If this is what DSI did, then the compensation VCAs may have a problem with control voltage feedthrough, which would cause a pop or a click when going abruptly from a low note to a high note. Or, urosh may be right about the DCO only changing frequencies at the start of a cycle, which means that if you have a very fast envelope, and you are going from a low note to a high note, you may hear up to one whole cycle of the low frequency at the start of a note before the frequency changes.

Speaking of envelopes, though: One thing people don't realize is that vintage analogs, for the most part, have very slow envelopes compared to today's synths. Everybody today wants nice sharp envelopes, but it does tend to expose glitches in the oscillator circuitry, and it isn't just DCOs that have this problem. A lot of vintage VCOs are not really capable of instantaneous frequency change; there's always a little bit of slewing, even with the portamento set to zero. I've noticed this a little bit with my EML 101; I think the integrating capacitor itself loads down the charging circuit a bit. And some of the old comparators had problems with over/undershoot. There's also the problem of what happens when you instantaneously turn on a VCA that is being fed by a free-running oscillator. If the waveform at that moment happens to be near a peak, the output will have a sharp transient where it turns on, that will be noticable if the waveform doesn't contain a lot of upper harmonics. (This is exactly what causes Hammond key click; the waveforms are almost sine waves, and the turn-on transients are very noticable.)

Re: Technical discussion of DSI MEK and it's DCO pop

PostPosted: Sun Jul 05, 2009 6:01 pm
by Jabberwalky
I now own Tallow's old MEK actually, but it appears to happen in every evolver. If I'm understanding Urosh correctly, it could be fixed with a software update. I wonder if we would be able to get an explanation from Dave himself or Dave Bryce. If enough of us want it fixed, it could happen in another OS possibly. Not a huge deal really, but it would be nice.

Re: Technical discussion of DSI MEK and it's DCO pop

PostPosted: Mon Jul 06, 2009 3:06 pm
by gd
The P 08 has the same issue but then again uses the same DCO's anyone with a Mopho care to comment.

Re: Technical discussion of DSI MEK and it's DCO pop

PostPosted: Wed Jul 08, 2009 1:45 pm
by Jabberwalky
I'm betting the mopho does the same thing. If it doesn't than that means there's a way around it.

Re: Technical discussion of DSI synths and their DCO pop

PostPosted: Wed Jul 08, 2009 2:30 pm
by zoomtheline
As soon as I saw the first post I wondered if you are explaining something that I noticed straight away with the mopho! I have never played any other DSI keys before so I can't comment on those.
I guess i'll read that article and see if we are talking about the same thing

Re: Technical discussion of DSI synths and their DCO pop

PostPosted: Wed Jul 08, 2009 2:46 pm
by zoomtheline
hmmm, while I can hear the odd pop and such within the Mopho's sounds I am not bothered by them as I assumed they were a character of all analog circuitry.

I also don't see all the fuss about the samples that the bloke posted, I heard what he was talking about but didn't see them as a terrible thing. I was under the impresssion that analog osc are loose and unpredictable and can change within warming up time etc. Thats why people love analog because its alive... non?

anyway I'm going to have a bash on the Mopho later to see if I notice more.

i'm not worried to be honest!

Re: Technical discussion of DSI synths and their DCO pop

PostPosted: Wed Jul 08, 2009 7:18 pm
by splitpoint
So is this "bug" the reason that everyone is unloading their PEKs on ebay for fire-sale prices this week or is it just the crappy economy? I'm seriously thinking of picking up another pair of PEKs if this fire sale continues.

Re: Technical discussion of DSI synths and their DCO pop

PostPosted: Wed Jul 08, 2009 7:33 pm
by masstronaut
I doubt it. This is really no big deal at all. Under most circumstances you'll only hear it if you go out of your way to, even then it's nothing much, and by the time it's in the mix... Honestly you'd have to be overly anal to be bothered by it at all. Certainly nothing that's going to stop you getting good sounds out of a synth.

Is that in the US PEKs are going cheap? No super deals in the UK really.

Re: Technical discussion of DSI synths and their DCO pop

PostPosted: Wed Jul 08, 2009 7:57 pm
by splitpoint
Yeah, Ebay US. One just sold for $965 and there are several around $1k with no bids right now along with one that is at $676 with only 8 hours to go.

I love my PEKs, best synths I've ever owned and I've tried just about everything at one time or another.

Re: Technical discussion of DSI synths and their DCO pop

PostPosted: Wed Jul 08, 2009 11:06 pm
by tallowwaters
I noticed for the most part, but there are so many gain stages, slop, and delay taps in the Evolver that it was really hard to pick out in a mix anyways. I guess it would be annoying for some, but in 15 years this will be one of the reasons everybody loves the Evolver series, warts and all.

Re: Technical discussion of DSI synths and their DCO pop

PostPosted: Thu Jul 09, 2009 12:23 am
by Jabberwalky
It's no big deal to me, the synth is incredible. It's an interesting discussion however, and I learned a lot about how DCOs really work.

Re: Technical discussion of DSI synths and their DCO pop

PostPosted: Thu Jul 09, 2009 12:37 am
by masstronaut
It is interesting, but I wouldn't want anyone to get the impression it's much of a negative strike against the DSI gear. An option to have the OSCs reset on note-on might still be nice though, if that's what it is.

Re: Technical discussion of DSI synths and their DCO pop

PostPosted: Thu Jul 09, 2009 2:18 am
by Stab Frenzy
I always thought that pop was from really fast envelopes. If it ever didn't work in the patch I was using I'd just increase the attack time and it would go away, problem solved.

$1k PEKs??!! If only postage down here wasn't so much I'd be all over one.