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SSM/CEM Chips, Do i understand correctly?
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xanderbeanz
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17th January 2013
Old 17th January 2013
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SSM/CEM Chips, Do i understand correctly?

I just wanted to check whether i've got all this info right:

From what i understand, before these chips came along, all synthesizer electronics were discrete, a bunch of capacitors and transistors and cogs and wheels (joking about the last 2 XD) then, sometime in the 80's when microchips started to become cheaper and cheaper, they miniaturized alot of these components and bunged them on a chip, so all the wiring turned into traces on the chips, and the transistors themselves became the chip's complex set of gate arrays.

So they did a VCO chip, a VCF chip, etc, (I understand my Mono/Poly has a load of them in) and then they either wired these up to pots and sliders like they always used to (like in the M/P) or, they used a CPU to digitally control them (like in Prophet 600) now, the primitive CPU's lead to a bit of stepping between values, as the analogue values were crudely converted to digital ones using 4-8 bits (i think it's 5bit on the poly 800 for example)

Of course, DCO's came in later, further integrating oscillator circuits into the digital domain, but for now, lets discuss 2 key things.

1. Did i get most of that information right? Is my basic understanding of the CEM/SSM process ok?

2. What exactly is lost in the miniaturization of the circuits? for example people rave on about the SH2 for it's big "discrete" oscillators, can CEM or SSM oscillators ever hope to compete with discrete ones if they're still voltage controlled and not sterile in terms of pitch? Does the chip making process take out a load of voodoo magic away from the oscillator circuit? Also, what about filters? I really like my M/P's SSM 2044, and i really like my C64's sid filter, but is there something missing in the design? could a chip ever really compete with a real moog ladder filter? (I'll probably be buying a moog later this year for THAT sound anyway.)

None of this really matters of course, lots of chip based instruments sound great, but the topic fascinates me and i'd like to know more

Discuss...
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17th January 2013
Old 17th January 2013
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1. Yep, that's the gist of it
2. Super tight control of every single component. At the end of the day though, the whole is greater than the sum of the parts. There were plenty of curtis and SSM parts that sounded very good (Prophet 5?). The main thing to understand is what these chips did was to enable big polys to become affordable enough for most every body. Ever seen the inside of the Korg PS synth? Its a nightmare of huge voice boards, super expensive to make where everything has to be discrete. With filters/oscs on single chips you can have 6 voices on one board easily.

Obviously, it went too far at one point where you had the whole synth on one chip (CEM3394->barf) where too many corners were being cut for the convenience of price and usability so everything started to sound the same and analogs fell out of favor
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17th January 2013
Old 17th January 2013
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The late 70s, not the 80s, is when these chips began manufacture. But otherwise, you're spot on.
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17th January 2013
Old 17th January 2013
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Quote:
Originally Posted by xanderbeanz View Post
2. What exactly is lost in the miniaturization of the circuits?
Each component in this miniature circuit inside the chip is made of exactly the same material (talking about material purity) and thus will have exactly the same properties. It is very unlikely that few microns away, next transistor will behave a bit different, such as you would expect when you have two "hardware" transistors made during two different runs, of materials with different purity, neither their properties perfectly match.

Further more, if heated, components inside the chip will heat up together and no difference will occur between individual parts. Their thermal properties are most likely the same down to xxyy decimal points. Going to chip design has its benefits/drawbacks. In VCO circuit design, you might want to avoid 100% identical component values. OTOH in ladder filter circuit you want transistors to be as close match as possible.

Keep in mind that BIG part of the sound is the chip's surrounding electronics, gain staging, auto tune routines (on CPU controlled synths), heaters, etc. Yes, SH-2 does indeed sound BIG. Its single oscillator in PWM eats all 4 Monopoly's. OTOH, SH-2 can not produce that characteristic (i call it hollow/fat) charming sound of SSM VCOs. So there's no real winner in here. Nothing that one should worry about. SSM LP filters sound phenomenal. Probably second best thing to Moog ladder.

Recommended to watch: http://www.youtube.com/watch?v=z47Gv2cdFtA
xanderbeanz
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17th January 2013
Old 17th January 2013
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Thanks guys
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17th January 2013
Old 17th January 2013
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Quote:
Originally Posted by xanderbeanz View Post
Of course, DCO's came in later, further integrating oscillator circuits into the digital domain
Only the control. A DCO still spits out an analog voltage. Digital means that there's an extra step involved - D/A conversion (but that's for PPG Waves or DW8000s)

Quote:
Can CEM or SSM oscillators ever hope to compete with discrete ones if they're still voltage controlled and not sterile in terms of pitch?
The Alesis Andromeda uses Anadigm chips. How sterile are those?
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17th January 2013
Old 17th January 2013
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Quote:
Originally Posted by Yoozer View Post
The Alesis Andromeda uses Anadigm chips. How sterile are those?
VCOs are in free flow (if you let them by disabling all the tuning) but the signal path is a bit on the clinical side, particularly the filter section. Also there is some sort of bandwidth limit - you can't get that VCO high sheen such as what Jupiter 8's VCO produce. IMO, it definitely sounds like a chip based synth. Not that it sounds bad. It's a killer synth!!! And i'm sure it will sound better as it ages.

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