Korg DW8000 built in Chorus effect?

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madtheory
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Re: Korg DW8000 built in Chorus effect?

Post by madtheory » Sat Jul 29, 2017 10:20 am

Yes, I didn't think there was really a level difference :).

The rest of your assessment still doesn't make sense to me. In the circuit there is only a single mono delay line, its signal is split to both outputs.The second op-amp stage reverses the polarity of one output. That is the only difference between left and right outputs. Yes, the delay time is modulated. But that signal is sent at equal level to both channels. The polarity flip comes AFTER the modulation. And I think you are confusing polarity with phase. Yes it is possible to phase shift a signal by 180 degrees, but in audio that is often a different thing to reversing the polarity. Phase shifts will often be different for each harmonic in the signal. That is why it sounds so interesting, it is harmonically complex even when static (e.g. comb filtering). A polarity shift affects the entire signal equally, it is much simpler electrically and far less impressive to the ear.

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Re: Korg DW8000 built in Chorus effect?

Post by Mooger5 » Sat Jul 29, 2017 4:52 pm

OK, polarity change is not technically the same thing as phase reversal, but it is in practical terms. Just follow.

Keep in mind before modulation the chorus is almost a copy of the dry signal so obviously post modulation they still have a lot in common.

Consider the dry signal and the chorus as two identical oscillators; same waveforms, same pitch, same amplitude. If you detune one by a slight amount you´ll hear the oscs cancelling at times when they run at opposite phases and louder when in phase.
Similar thing happens at the DW6K output. IF the chorus´ polarity was the same at both channels just like the dry signal is, what you´d hear would be akin to the situation described above, and both channels would sound identical like dual mono, with cancelling and amplitude doubling on both at the same time; no movement or autopanning ilusion between channels. However as the chorus has its phase reversed on the right channel, what happens is there will be cancelling at one channel and at the same time there will be amplifying at the other.

Examples:

- Take some abstract values, say +5 and -5.
Everytime the dry signal reaches +5 on both channels (obviously because they´re phase coherent for the dry signal) and the chorus signal on the left happens to be in phase with the dry signal, reaching +5 as well, the sum of the signals will be +10. On the right channel we will in turn get +5 on the dry signal and -5 because of phase reversal of the chorus. They cancel each other out. So we have left louder than right.
- As well, when the dry signal reaches +5 but the chorus signal is at -5 at that time due to the pitch shifting, the sum on the left will be zero. On the right we have dry at +5 and chorus at +5 too. Sum is +10. Right channel louder.
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Re: Korg DW8000 built in Chorus effect?

Post by madtheory » Sat Jul 29, 2017 8:28 pm

But the chorus signal is phase coherent on the DW6000, because there is only one delay line! It is the same chorus signal on each side, because there is only one; but the polarity of this chorus signal is reversed on one side. So when both sides are added together, the chorus signal is cancelled and the dry signal remains. In the same way, in a balanced line noise is cancelled at the receiving end except that in this case the two opposing signals are electrically identical (in a balanced line there will always be a tiny difference because the noise signal is being induced on two cables with a little distance between them).

If there were two different chorus signals you would be correct, but there are not. There is only one difference, and that is polarity, not modulation. The chorus signal on the left is always exactly opposite to the chorus signal on the right.

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Re: Korg DW8000 built in Chorus effect?

Post by Mooger5 » Sat Jul 29, 2017 9:47 pm

You got a point. That´s its weak side, isn´t it. All in all I find it a clever solution provided this artificial stereo image doesn´t happen to be converted to mono afterwards. There´s always the 25% of wet signal, but it´s on the low side. You know what I´ll run a sort of simulation and report my findings regarding the inbalance.
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Re: Korg DW8000 built in Chorus effect?

Post by Mooger5 » Sat Jul 29, 2017 10:30 pm

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Re: Korg DW8000 built in Chorus effect?

Post by Mooger5 » Sat Jul 29, 2017 10:33 pm

With Chorus ON. In phase with the dry signal.

http://tinyurl.com/yc9oychk
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Re: Korg DW8000 built in Chorus effect?

Post by Mooger5 » Sat Jul 29, 2017 10:35 pm

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Re: Korg DW8000 built in Chorus effect?

Post by Mooger5 » Sat Jul 29, 2017 10:43 pm

Just the Chorus. Only 25% left after "monofication", alright.

http://tinyurl.com/y7hxt442
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Re: Korg DW8000 built in Chorus effect?

Post by madtheory » Sun Jul 30, 2017 8:22 am

Mooger5 wrote:With Chorus OFF.

http://tinyurl.com/y9x279t7
That can't be right. There's already a 25% difference in voltage between L and R without the chorus added? I don't see those R values on the schematic?

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Re: Korg DW8000 built in Chorus effect?

Post by Mooger5 » Sun Jul 30, 2017 2:17 pm

The values are per the manual. KLM-711, IC2 and all the resistors around. They form the output stage.

I simulated this circuit this morning,
routing the outs to a differential amp and I'm baffled. The resulting mono out is nowhere near null, nor even the 25 per cent.

I must be doing something wrong. I'll run both channels through a summing amp. If I get the same results as of this morning then I'm officially clueless.
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Re: Korg DW8000 built in Chorus effect?

Post by Mooger5 » Sun Jul 30, 2017 2:43 pm

OK, Chorus at 5 and Dry at 0 merged to mono gives 1.25, which is 25%. ..

Soething went wrong with the diff amp.

http://tinyurl.com/y8hmraud
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Re: Korg DW8000 built in Chorus effect?

Post by madtheory » Sun Jul 30, 2017 8:34 pm

I think you have it wired wrong. Where you have the outputs is actually where the VR is for chorus level control. Those two op-amp stages in IC2 are in series. It is still a mono signal at that point. The polarity reversal happens in IC1 I think?

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Re: Korg DW8000 built in Chorus effect?

Post by Mooger5 » Sun Jul 30, 2017 11:45 pm

The circuit is definitely wired correctly. It´s a stereo output, the VR is the volume slider and IC1 is the headphone amp. Follow the lines more carefully. Strange implementations can sometimes be intimidating but with a bit of preserverance it all starts to makes sense.
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Re: Korg DW8000 built in Chorus effect?

Post by madtheory » Mon Jul 31, 2017 8:42 am

I don't think perseverance is an issue for anyone here LOL! OK, I still don't really get it. Where does the polarity flip happen? Does the DW8000 do the same thing? Why is the DW6000 different in the way it fakes stereo compared to the SDD3000 and 2000?

I've just checked with some recordings I have of DW8000, and it seems to me the chorus is entirely cancelled out when we do L+R but I am not certain of that at all. Hard to really tell because the chorus amount is subtle. On the goniometer I see a sawtooth pattern modulation left to right. I don't understand how that can be done with only one delay line. I'm missing something here!

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Re: Korg DW8000 built in Chorus effect?

Post by Mooger5 » Mon Jul 31, 2017 9:08 pm

I looked up and the DW8000 has the left and right wet channels out of phase too. Like the 6k, it´s meant to be used in either "stereo" or just the Left Out for mono. But this time there´s no imbalance between the outputs, they´re both at unity gain.

I´ll explain the 6k later.
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