Karplus strong

Discuss John Bowen Synths - Solaris
Weston Underwood
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Karplus strong

Post by Weston Underwood »

Any advice on creating a tuned karplus strong sound. I've had a play with the comb filters and the delay effect with the spdif output returned to a second filter. I couldn't think of another way to route to sound post effects back into the filter but as I write this I wonder if setting up a loop with the comb filters via a mixer might be the way ahead.

Any hints or tips of a specific Solaris nature? Particularly tuning the sound.

Thanks in advance!
Zahush76
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Re: Karplus strong

Post by Zahush76 »

I'm no expert, but i can say this. Ken Elhardt made some one of the banks, and designed some strings, guitar etc - and insisted he didn't use any Karplus strong.
So i think going to Ken's presets and following what he did and how he programmed his sounds seems like a good starting point.
John Bowen
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Re: Karplus strong

Post by John Bowen »

Technically the comb filter is already that - it's a delay line with positive or negative feedback. You should only need to put it in near oscillation and send a short noise burst to excite the filter. The Damping factor is the lowpass filter in the feedback loop.

However, Ken said that he expected to be able to make good K-S sounds with it, but that we had something 'wrong'. For my part, I had a difficulty as well in getting really what I expected. More research and input from anyone who has more experience with K-S would be appreciated!
Weston Underwood
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Re: Karplus strong

Post by Weston Underwood »

Thanks Zahush

I thought of that, but then as you say Ken said he didn't use KS so I can't check his sounds for how to use it!

Thanks JB. I agree that the comb filter doesn't sound quite right, not as fattened or hollowed out as others Ive used (like the one on the octatrack for example). On the OT the controls are:

PTCH (pitch) controls the resonance frequency of the comb filter.
TUNE changes the pitch by up to 2 semitones up or down.
LP controls the cutoff frequency of an lowpass filter in the feedback signal. FB controls the gain of the feedback signal.
MIX controls the dry/wet signal mix.

My problems are however more likely to be user error than anything else but if Ken can't make it work I'd suggest its broken!

If its working maybe the developer can show you an example of a K-S sound, I find a developer demo a great way of confirming functionality!

Finally maybe an email to Elektron HQ might help, they seem a nice bunch and its likely they'd help out, the Solaris and octatrack aren't what you'd call natural competitors.

BW
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Re: Karplus strong

Post by John Bowen »

Weston Underwood wrote:Thanks JB. I agree that the comb filter doesn't sound quite right, not as fattened or hollowed out as others Ive used (like the one on the octatrack for example). On the OT the controls are:

PTCH (pitch) controls the resonance frequency of the comb filter.
TUNE changes the pitch by up to 2 semitones up or down.
LP controls the cutoff frequency of an lowpass filter in the feedback signal. FB controls the gain of the feedback signal.
MIX controls the dry/wet signal mix.

My problems are however more likely to be user error than anything else but if Ken can't make it work I'd suggest its broken!
Well, I would say it's not a thing of the comb filter being 'broken'; what we may have here is a difference in design philosophy and/or understanding of what the algorithm should be.

For your octatrack parameters, I see:

1) PTCH and TUNE as the Cutoff Frequency
2) LP as Damping
3) FB as Resonance control

MIX would be something we don't have for the Comb filter.

Does that seem correct to you?
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Re: Karplus strong

Post by John Bowen »

And to add a little bit more, I believe the Solaris Comb filter is technically a filtered feedback or feedforward structure.
Weston Underwood
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Re: Karplus strong

Post by Weston Underwood »

I've been experimenting more with chains of comb filter and can get slightly unstable sounds which track at the upper 2 octaves of the keyboard but break down toward the lower ranges into harmonics. Still not the classic KP sound.

I wonder if the difference is that pitch / tune on the octatrack implementation is possibly cutoff and sample rate. Could the lack of control of sample rate be the limiting factor, allowing the ability to control pitch with either resonance toward the cutoff filter (which I would imagine will tend toward a sine wave - which is what it sounds like) or frequency controlled by changing the frequency of the delay, thereby keeping the wave itself in oscillation via feedback within the loop structure. (I am however making this up as I'm going along!)

I looked at the equations at the web and knew immediately they are way beyond my understanding!
Zahush76
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Re: Karplus strong

Post by Zahush76 »

Weston Underwood wrote:Thanks Zahush

I thought of that, but then as you say Ken said he didn't use KS so I can't check his sounds for how to use it!
I think you didn't quite understand what i was trying to say. Of course Ken didn't use KS - since there isn't really a Karplus strong engine on the Solaris.
What he said was that he could imitate KS like sounds, using the features onboard the Solaris (i.e. clever use of envelopes, lfo's and other tricks). So go ahead and check out how he made his sounds.
Weston Underwood
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Re: Karplus strong

Post by Weston Underwood »

Sorry! I get your drift now. The plucked strings that he did aren't bad but the attack is a bit too soft. I love the crisp attack provided by true KS.

From the point of view of a KS engine, it should work, the components for KS are there, a burst of noise, a delay, a filter and a feedback loop. Somehow the effect isn't quite right and I wonder if its the inability to control the time dimension on the delay that is the issue.

I'll study Ken's patches in the meantime as a substitute!

I've no doubt that either someone will come along and demonstrate how to do it or in the fullness of time the OS will be tweaked to accommodate traditional KS even if it can't now. I love the KS output of the accelerator and it had been a close thing as to which machine I got. John's re-assurance to me regarding KS was one of the reasons I bought the Solaris in the end so I hope for solution. viewtopic.php?f=1&t=16035&p=18910&hilit ... ong#p18910

Jimmy V said that he'd managed it so maybe he'll chip in.

Best wishes
Weston Underwood
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Re: Karplus strong

Post by Weston Underwood »

I've been trying on and off during the day, in between,cutting the grass, strimming and training my hops (yes I know not very rock star).

Finally, at 20 minutes to one in the morning I've made it work, a nice plucked rich sound. I'll describe it tomorrow and try to get the hang of posting patches on the site. Basically it was a combo of comb filter, white noise and two mixers and filters, with the richness added by a rapid 10ms envelope strafing the cutoff filter in the comb.

Add some reverb and jobs a goodun.

BW
Patate le mgae
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Re: Karplus strong

Post by Patate le mgae »

Weston Underwood wrote:I've been trying on and off during the day, in between,cutting the grass, strimming and training my hops (yes I know not very rock star).

Finally, at 20 minutes to one in the morning I've made it work, a nice plucked rich sound. I'll describe it tomorrow and try to get the hang of posting patches on the site. Basically it was a combo of comb filter, white noise and two mixers and filters, with the richness added by a rapid 10ms envelope strafing the cutoff filter in the comb.

Add some reverb and jobs a goodun.

BW
Nice, i've tried some hours and didn't manage to obtain it.
In fact, the only thing wich is missing to obtain KS sounds very easily is the possibility to modulate the effects parameters with all the cv family : here "note" will be enough.
I manage to obtain a nice KS sound using the delay, but it's a fix sound ; it doesn't follow the keyboard, obviously because i can't assign the rate of the delay to the note parameter.
Weston Underwood
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Re: Karplus strong

Post by Weston Underwood »

There you go. Some of them may not be KS, all of the KS ones have KS in the name! - These presets could do with a better naming structure!

Should be a reasonable starting point.

Let me know what you think and post your improvements. Feel free to send cash and commissions.

BW
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Patate le mgae
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Re: Karplus strong

Post by Patate le mgae »

Nice work Weston, very good idea to reinject the second VCF in the first mixer, the sound is very punchy.
And the combination of two or three serial VCF does the job.
I was exploring another way, i shall give you my sounds when i'll have complete some more.

For the othes user : if you try to use those sounds : for three of them only sp/dif is assign, if as me, you are using output 1/2 you'll have to assign "synth" to them.

Weston : why do you reinject SP/dif in mixer 1 ? I don't use this connection and don't understand the reason.
John Bowen
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Re: Karplus strong

Post by John Bowen »

Well, I owe somewhat of an apology to Weston, it seems. My understanding of how the Solaris handles its Comb filter was incorrect - I asked the main coding engineer, Klaus, about how to create actual KS patches, and also, to read this thread...here was his response:
Interesting to read - getting a Karplus Strong patch seems to be more intriguing than I thought.

In short with the Solaris comb filter there are no means to pluck the chord (= fill the delay line with undamped noise burst).

In a KS patch this is usually done at every start of a note. So there is a special gate or initialization routine with a random generator.
Sometimes even a recording of a plucked chord instrument is used to fill the delay line.

It seems the people in the Forum fortunately found a solution.
Using envelopes for the excitation noise burst sounds like a good idea - I'm looking forward to listening to that on a Solaris.
There you have it. I've asked him if we could make a variation that would allow an easier solution than what Weston has put together in his example Presets, and we will be discussing this and other things when I'm there next week.
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Re: Karplus strong

Post by John Bowen »

So, we had our meeting yesterday, and Klaus states the best way to solve this will be to add another Mode to the Comb filter. I'm not sure when he can do this, but I am sure this will be easier to implement here.
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