using cp-251 with macbeth m3x

[scimmiamk]

Hi there,
I've recently bought a cp-251 to control my M3X. My main needs where adding a proper portamento to the M3X, which I was intending to do with the lag processor, ad to use the S&H to control the filter cutoff.
I did the latter with no problem, but when it comes to portamento there's a lot of weirdeness happening.
My idea was to connnect M3X cv out to lag processor in, then from the lag processor out to the attenuator and finally back to the M3X.
Rise and fall seems to work backwards, and the synth struggles to stay in tune.
Can the s-trig configuration of the other cv in and out of the M3X be responsable for this?
thanks
David

[Portamental]

There is a difference between a CV and audio waveforms. The CP-251 different sections can process either or both or none depending on the situation.

In order do to it's job, the lag processor needs to know the frequency of the signal fed into it. The only frequency the lag processor knows about is the CP-251's own LFO rate. BTW, the LFO is both a CV and audio waveform (although sub audio if below 20hz). For that reason, the lag processor is used mostly in conjunction with the CP-251 LFO output.

You can not achieve portamento with the lag processor using a pitch CV. The pitch CV is a steady DC signal (although variable within it's range). The CP-251's lag processor does not care about a pitch CV and knows nothing about the keys you press or release, the gate signal, etc. In other words, a pitch CV does not carry any frequency, it only tells another circuit to generate an audio signal of a frequency that is calculated proportional to the DC value of the pitch CV.

[Mr Shave]

I agree with most of what you say Portamental, but i think you are wrong on the pitch CV thing.

Yes, its a DC signal and not audio, but the lag processor should still function with that. The lag processor doesnt care what kind of signal you put into it, its going to slew that signal the new value. So if you have a square wave (audio or LFO), you can kind of get a triangle wave out of it (depending on the settings of the rise/fall knobs). If you have a stead 3V that drops to 2V at a random time, the lag processor will slow that drop depending on the fall knob is, and will slow the rise depending on the rise knob if you then feed it 4V (for example).

I dont know much about the M3x, but i dont think your setup will work as you expect. The pitch Cv out from the Macbeth is generated when you play a note (i presume with a midi controller). That note determines the voltage of the pitch CV out. If you take that CV and put it to the lag processor, you will get a slewed CV out of it (as you expect), but if you put that back into the CV input, you are going to create some kind of feedback loop which is probably causing your weird tuning issues. Because now you have an initial pitch created by the midi note (converted to CV inside the synth), that goes to a lag processor, which then goes to the pitch input CV (but you've already created a pitch CV inside the synth)... Thinking about it, i imagine you could get some pretty far out sounds like this, but its not going to function like a proper glide...

If you want to use the CP251's lag processor to get glide on the macbeth, i would imagine you would need to generate a pitch CV from somewhere other than the macbeth (LP, Voyager, Midi-CV interface etc), put that CV into the lag processor, and then take that output and send it to the pitch CV in of the macbeth. It should work that way.

I think... haha, cheers

[Portamental]

In order to rise and fall a signal (even a positive CV), the CP-251 needs a time frame, and that time frame is that of the CP-251's LFO rate. So the lag processor will TRY to slew an incoming CV, but with rather "unpredictible" results, related anyway to the LFO rate, just like scimmiamk experienced. It can lead to interesting pitch effects, but can hardly be used to simulate a portamento. The lag processor is designed to work with AC (audio) signals.

[Vitja]

Well, I have to say that I disagree with this...
I'm not sure if Lag is connected with LFO but I use it with envelope from MP, and I use sharp Env, so I can make longer decay time and longer attack time with it, and LFO has no effect on it...
And I also control pitch with it, and it does a decent portamento effect.
So what I suggest is that if you have a CV that controls Pitch, you just run it through LAG and thats it.

[c7sus]

I don't know where you are getting your info Portamental, but you should refer to the CP-251 manual.

The LFO has nothing to do with the lag processor other than as a source for a CV waveform. And the lag processor most certainly isn't for processing audio frequencies only.

[Portamental]

And the plot thickens, interesting.

I don't know where you are getting your info Portamental, but you should refer to the CP-251 manual.

I just did that, and spent an hour testing configurations using pitch out, pitch in, and just about any combination of both modulation busses on the Voyager Old School.

I stand corrected. No relationship to the LFO rate. The time constants are set by the knob position of the LAG section. I could achieve (besides a number of interesting sound effects, including a double LFO sample and hold type effect, without using S&H) a good portamento effect. Problem is it is more in the realm of sound effects than musical expression. The thing is that the incoming (from the CP-251) pitch CV is added to the internal keyboard pitch CV, so the notes you play are not the ones you press on the keyboard. Maybe with some more work using the attenuator and mixer offset, it can be refined, but that would hardly qualify as achieving easy portamento the way it should be.

Edit: manual states : The Lag processor provides a means of slowing down a rapidly changing control waveform.

[scimmiamk]

Thanks for the answers.
I'm not sure if I can sort this out, but on the other end I'm experiencing some weird and unconvetional sounds I'd never achieve without the cp.
This Cv affair is really opening some interestig perspectives.
Could I get that portamento effect more easily via a ribbon controller a la Doepfer R2M?

[Portamental]

It seems to me either an A-170 or A-190-2 would be closer to what you need.

If I have a bit of time this week, i'll check out what I can come up with using the A-190-2 and my model D, which is s-trig, like the MacBeth.

I suppose you plug a midi keyboard into the MacBeth (and the midi-to-CV conversion is internal), right?

[scimmiamk]

yes
I use a yamaha kx 25 and inside the m3x is hosted a kenton pro solo midi to cv interface

[Portamental]

Did I read this right? The MacBeth people have decided to, instead of designing their own, let's say, subcontract the midi-to-CV to Kenton and include the circuits inside the M3x? Nothing wrong with that, makes sense actually. Just want to make sure.

[scimmiamk]

yes that's what Ken Macbeth did, I read somewhere that he didn't want to deal with the digital part

[Portamental]

Allright... been playing with my toys... not getting to where I think you want to be with portamento from a CP-251.

The A-190-2 does nice midi-to-CV with Glide (portamento).

The only thing I can suggest (you're the boss) for your Macbeth is to bypass the Midi-in (using the Macbeth with CV's only) and connect your controller to a Doepfer DarkLink, which is essentially a stand alone version of the A-190-2. Just plug and play. Some limitations may apply, like the 0-5v limit of the unit, for a five octave range. From what I understand, you can use some transpose, but since the unit is only 0-5, you may not be able to play some lower notes like a Moog Voyager for example, which is comfortable with CV's in the negative range. It's only an educated guess since I don't have hands on a MacBeth to tweak around.

Look it up on the Doepfer page and see if it suits you.

[scimmiamk]

thanks

[cliffman]

Wow, am amazed at this much trouble.

Try this - get a voltmeter.
Send a pitch CV out your pitch CV out-thing (Kenton 2k in my case)
Measure the voltage.
Send a pitch CV one octave higher out.
Measure the voltage. Should be previous voltage +1V

Then,
Plug CV out of your pitch CV thing into IN of Lag.
Measure voltage coming OUT of Lag. Should be exactly the same voltage,
regardless of where the knobs are.

Then,
Plug CV out -> Lag in
Lag OUT -> CV in of you OSC.

Should Just Work! (At least it just did for me)
Turn the knobs on the Lag, portamento!, turn fully CCW, no portamento.
Hope this helps.