Korg Poly 800's VCA(s?)

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Korg Poly 800's VCA(s?)

Post by oryjen » Fri Jan 11, 2008 7:32 pm

Hello,
I read everywhere on the web, that the Poly 800 only has ONE VCA as ONE VCF...
But some of my friends that used to own one, say that it has 8 VCAs while only 1 VCF....

Where's the truth?

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Post by Synthaholic » Fri Jan 11, 2008 8:45 pm

If it only had 1 VCA, it would essentially be a mono synth, since it wouldn't be able to turn on/off each voice/note individually.

So, unless it has some sort of voice gating separate from the VCA, it would have a separate VCA for each voice.
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Post by OriginalJambo » Fri Jan 11, 2008 10:50 pm

Not trying to hi-jack this thread but this is exactly the kind of confusion that paraphonic "polyphony" creates.

As far as I'm aware you can play 8 different notes on the Poly-800 at a time, but they won't have their own envelopes, VCFs or VCAs so either they'll share the envelope of the first voice or the envelope will retrigger for all voices every time a new note is played.

In other words you can't have two notes sweeping in or out with the VCA or VCF at difference times.

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Post by Automatic Gainsay » Fri Jan 11, 2008 11:33 pm

Synthaholic wrote:If it only had 1 VCA, it would essentially be a mono synth, since it wouldn't be able to turn on/off each voice/note individually.

So, unless it has some sort of voice gating separate from the VCA, it would have a separate VCA for each voice.
Plenty of polyphonics have only one VCA... it just means that if the sustain is off, any notes played after the single ENV has opened and closed the VCA will not be heard. If the sustain is up, then the VCA will stay open while notes are being played and and any notes played while the VCA is open will sound as on-off organ-like events.
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Post by nathanscribe » Fri Jan 11, 2008 11:44 pm

The Poly800 is either 4 or 8 note poly, depending how you set it. There is 8-voice mode, in which the first oscillator is used for each voice, and 4-voice, in which both oscillators are used for each voice.

The 2 oscillators each have their own volume envelope, so in 4-voice mode you can hold a key and have one osc fade in only to be joined by another a little later. Handy.

The filter has its own envelope, and this is where the problem lies: there is indeed only one filter for all the voices. So regardless of the volume of each oscillator, the filter envelope is simply either retriggered or not (according to setting) on each new note.

The filter envelope also controls the noise level.

As far as quantity of VCAs goes, there is a custom IC in there that bears a VCF and VCA, so without putting any real analytical effort in, I presume there is indeed just one VCA. How the individual voicing is implemented I am not entirely sure, but given the nature of the oscs (switchable squares at various intervals) I imagine it to be controlled at the oscillator stage rather than the post-filter stage, as would be the more usual arrangement.
Last edited by nathanscribe on Fri Jan 11, 2008 11:50 pm, edited 1 time in total.

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Post by OriginalJambo » Fri Jan 11, 2008 11:47 pm

2 VCAs with separate envelopes, but one VCF with an envelope? The Poly-800 sure is a weird one. :-k

Still, even if the Poly-800 has limitations it doesn't make it a bad synth - it's just good to know what to expect if you are thinking of getting one.

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Post by nathanscribe » Fri Jan 11, 2008 11:54 pm

Yep, it is a bit odd. I'd have to pore over the circuits to find out how it properly works, and I can't be bothered.

:lol:

I suspect it was an effort by Korg to make something they could label as poly-analogue and MIDI on the cheap. As with any limited synth, as long as you know what it does and doesn't do, you might be able to like it.

Actually, the envelopes aren't half bad - not the usual ADSR. They have a break point on the decay, followed by another rate which takes it up/down to the sustain level.

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Post by Box » Fri Jan 11, 2008 11:58 pm

As Automatic said most synths only have 1 VCA. But sadly the 800 only has one filter for ALL 8 OSCILLATORS/VOICES. I couldn't stand the thing. Every time I sat down with it I wanted to chunk it out the window. Glad I sold it, now I have my JX-8P with a filter for each osc/voice, the way it should be...
Last edited by Box on Sat Jan 12, 2008 12:04 am, edited 1 time in total.
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Post by OriginalJambo » Sat Jan 12, 2008 12:01 am

nathanscribe wrote:Yep, it is a bit odd. I'd have to pore over the circuits to find out how it properly works, and I can't be bothered.
I'm no guru, but I'd imagine it's a form of digital keyboard scanning coupled with dynamic voice allocation. Obviously would be a lot more basic than what we are used to now.
I suspect it was an effort by Korg to make something they could label as poly-analogue and MIDI on the cheap. As with any limited synth, as long as you know what it does and doesn't do, you might be able to like it.
Exactly.
Actually, the envelopes aren't half bad - not the usual ADSR. They have a break point on the decay, followed by another rate which takes it up/down to the sustain level.
Oh are the envelopes digital ones then? If they are that complex I'd expect it to be the case in an instrument that claimed to be affordable at the time.

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Post by nathanscribe » Sat Jan 12, 2008 12:12 am

OriginalJambo wrote:I'd imagine it's a form of digital keyboard scanning coupled with dynamic voice allocation.
I was referring to the way the oscillator levels are shaped - and the envelopes are at least digitally controlled - there are a few proprietary chips in the poly that I don't know anything about. I'm guessing the envelopes are within that lot somewhere.

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Post by OriginalJambo » Sat Jan 12, 2008 12:47 am

nathanscribe wrote:I was referring to the way the oscillator levels are shaped - and the envelopes are at least digitally controlled - there are a few proprietary chips in the poly that I don't know anything about. I'm guessing the envelopes are within that lot somewhere.
Hmm...interesting. Sometimes I wish I'd stuck in at Electronic Engineering so I'd be able to analyse schematics, but alas that was before I knew what synths even were.

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Post by Automatic Gainsay » Sat Jan 12, 2008 4:57 am

nathanscribe wrote:I suspect it was an effort by Korg to make something they could label as poly-analogue and MIDI on the cheap. As with any limited synth, as long as you know what it does and doesn't do, you might be able to like it.

Actually, the envelopes aren't half bad - not the usual ADSR. They have a break point on the decay, followed by another rate which takes it up/down to the sustain level.
As a person who remembers vividly when they came out, I can tell you that their biggest selling point was PRICE. Everyone was very excited about the notion of owning a synthesizer with all of the functionality it had for such a low price.

Just like today... "sure, it's got some limitations, but LOOK AT THE PRICE!"

Thankfully, I got a Juno 106 as a gift before I invested in a Poly 800. :)
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Re: Korg Poly 800's VCA(s?)

Post by Dirk » Sat Jan 12, 2008 6:55 am

oryjen wrote:Hello,
I read everywhere on the web, that the Poly 800 only has ONE VCA as ONE VCF...
But some of my friends that used to own one, say that it has 8 VCAs while only 1 VCF....

Where's the truth?
Very good question.

There's only 1 VCF inside the poly800, the NJM2069. So the 8 voices are not completely independant from eachother. The NJM2069 VCF chip also has a VCA build into it.
But when playing on it something strange happens: Set the release of the envelopes on max. Then when I play C1, let the key go, play C2, it cuts off C1. But when I play D1 after I let the key of C1 go, C1 stay's in the release stage (normal behavior).
The voice chip is a MSM5232, witch has 8 voices and is used in many old video games. Here you can find info on the MSM5232: http://www.mameworld.net/maws/mamesrc/s ... /msm5232.c
It seems that this chip also has 8 digital volume generators in it.

So to answer the question: The Korg Poly800 has 1 real analog VCA in it and 8 digital volume generators.
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Post by Dirk » Sat Jan 12, 2008 7:08 am

It seems that you can even put your own samples in the voicechip!
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Post by solderguy » Sat Jan 12, 2008 9:48 am

Yes - the "VCA envelopes" are done inside the OKI tone generator chip. If you ignore the VCF, the Poly 800 is a true 8-voice polyphonic board.

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