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"LFO per voice" for beginners

dsetto

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"LFO per voice" for beginners
« on: October 16, 2017, 12:08:51 PM »
I want a better understanding of how LFO is implemented in the Prophet '08. (I'm away from the synth.)

My first question is understanding the implication of "LFO per voice".

I understand an LFO can either be:
free running, key sync, or clock sync.

Imagine a scenario where LFO 1 is the only LFO engaged, it's free running, and it's modulating pitch (for the sake of easy forum discussion). I can control rate, shape and amount for LFO1. Let's say I've got shape at square, and rate set so that the pitch changes every second, and amount so that the pitch change is one octave. (For a fully sustaining sound, zero attack, and no other modulation.)

If I press and hold the C4 key, I believe I will hear the C5 and C3 pitches, alternating every second. Is this correct?

If I keep the C4 key held, and then press & hold the G4 key approximately in sync with a pitch change from the C4 key, what will happen?

I figure the following factors govern the results: 
- "LFO per voice"
- LFO1 is free-running

Without overthinking, I would guess that I would hear the alternations between G5 & G3 approximately in sync with the alternating C5 & C3 pitches. (Maintaining a single fixed time offset, that's a function of when I pressed the G4 key in relationship to the C5-C3 alternations.)





Re: "LFO per voice" for beginners
« Reply #1 on: October 17, 2017, 01:58:42 AM »
Moinmoin,

You are nearly right, as there is - in my opinion - a design fault in the LFO-key-syncing:
If You set the LFO waveform to square and keyboard sync to ON, the key will not trigger the LFO-square's rising edge but "in the middle" of the low phase. This has a bad effect on timing as You will have to hit the key a quarter of a cycle before You want the LFO's rising edge to become effective. :(
All Your syncing is delayed one quarter of a cycle, which will make You instantly mad (as well as Your fellow musicians, if You try to sync with their groove).

In Your example You will probably intend to sync the switching between C3 and C5 with Your keypress. What happens, however, is as follows:
  • keypress, C3 sounds for a quarter of a cycle
  • rising edge makes the note change to C5 after a quarter of a cycle for a half cycle's time
  • falling edge makes the note change to C3 after a three quarters of a cycle for a half cycle's time
  • next rising edge makes the note change to C5 after a five quarters of a cycle for a half cycle's time
  • ... and so on ...
If at any time in this sequence You hit the G at a change from C3 to C5 (or C5 to C3) and still have the sync set to ON, Your groove will be destroyed, as P'08 will not sync to a pitch change, but insert one f***ing quarter of a cycle at any keypress. >:(

Solution could be to switch syncing to OFF as soon as Your C3-C5-switching is established, which will of course not help You if You have to adapt to an existing groove or Your music is made interesting by funny little things like rests...
So in Your special case I would suggest to use the sequencer (If You do not need it for other things, that is)

HTH

Martin
« Last Edit: October 17, 2017, 02:00:30 AM by MartinM »

panic

Re: "LFO per voice" for beginners
« Reply #2 on: October 17, 2017, 07:06:55 AM »
Let's say I've got shape at square, and rate set so that the pitch changes every second, and amount so that the pitch change is one octave. (For a fully sustaining sound, zero attack, and no other modulation.)

If I press and hold the C4 key, I believe I will hear the C5 and C3 pitches, alternating every second. Is this correct?

No, only the triangle LFO is bipolar. What you will hear is C4 and C5 pitches.

Without overthinking, I would guess that I would hear the alternations between G5 & G3 approximately in sync with the alternating C5 & C3 pitches. (Maintaining a single fixed time offset, that's a function of when I pressed the G4 key in relationship to the C5-C3 alternations.)

No, what you describe is keysync behavior. With free running (ie no keysync), the offset will be regardless of when you pressed the keys.

dsetto

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Re: "LFO per voice" for beginners
« Reply #3 on: October 18, 2017, 12:27:03 PM »
Thank you for the responses. … I still don’t have time with my Prophet, but I’m curious about it.

… If You set the LFO waveform to square and keyboard sync to ON, the key will not trigger the LFO-square's rising edge but "in the middle" of the low phase. …
Hmm… On more digital machines I’ve observed the possibility to change where in the phase cycle an LFO would begin. In what you describe, it sounds like the LFO is beginning at 270 degrees.

By the way, at this moment, I don’t have a specific musical goal I am trying to achieve. Rather, I’ve described a specific musical example as a means of discussing how the LFO works.
——
… No, only the triangle LFO is bipolar. What you will hear is C4 and C5 pitches.
got it.

… I would guess that I would hear the alternations between G5 & (edit: G4) approximately in sync with the alternating C5 & (edit: C4) pitches. …
No, what you describe is keysync behavior. With free running (ie no keysync), the offset will be regardless of when you pressed the keys.
Ok.

I am trying to understand the concept that each voice has its own LFO. First let’s look at LFO1 in “free running” mode, and no other modulation. And two keys being pressed & held, so that only 2 voices sound.

are the following thoughts true?
1. Each voice has its own LFO

Let X be the same point in one LFO’s phase cycle. Let’s say X is “0 degrees”. Let it be LFO1.
2. In “Free Running” mode, there is no controllable correlation between the 0 degree points of the LFO of each voice. They seem to be random.
3. Question: Is the time distance between the 0 degree points of each of these 2 voice’s LFO fixed? i would think it is.
4. I would imagine LFO1’s rate control governs the rate of the LFO of both of these 2 voice’s LFO’s. Correct?

panic

Re: "LFO per voice" for beginners
« Reply #4 on: October 19, 2017, 02:10:26 AM »
No problem, I love theoretical exercises (currently don't have a prophet, so the same for me) and solving programming issues.

are the following thoughts true?
1. Each voice has its own LFO

Let X be the same point in one LFO’s phase cycle. Let’s say X is “0 degrees”. Let it be LFO1.
2. In “Free Running” mode, there is no controllable correlation between the 0 degree points of the LFO of each voice. They seem to be random.
3. Question: Is the time distance between the 0 degree points of each of these 2 voice’s LFO fixed? i would think it is.
4. I would imagine LFO1’s rate control governs the rate of the LFO of both of these 2 voice’s LFO’s. Correct?
Answers:
1. Yes
2. almost true. You can sync the LFOs between voices (discussed in another topic) if you turn keysync on, press 8 keys simultaneously, and then turn keysync off again. Now you have synchronized free running LFOs. Also, somebody told me once that on some DSI synths (I can't remember if it applies to the P08), the freerunning LFOs are initially synced between voices when you freshly load the preset (I never verified this).
3. should be, if they move at the same speed (of course, there are ways to program them to move at different speeds)
4. Yup.

I agree that compared to some other synths, the LFO section is pretty basic (no global, no adjustable phase, no hold, no one shot). But you get a lot of 'em! Third envelope provides you with a hold function. And as Martin said, don't forget the sequencer. As a note sequencer, I found it not very useful, but as a modulation source it is excellent! Using the slew function with it, you actually can use it as an LFO of which you can determine the shape yourself.

Re: "LFO per voice" for beginners
« Reply #5 on: October 19, 2017, 02:40:36 AM »
dsetto asked whether following thoughts were true, and I am not sure if I understand him - and panic's answers - right. So I try to be as precise as possible:

Quote
1. Each voice has its own LFO
What do You mean by voice?
  • If Oscillator: No, and that is a good thing, as it saves LFOs and normally leads to "musically useful" things. You may choose LFO phase to "survive" new keypresses or not (by setting keyboard sync to OFF or ON, but with the general phase problem described by me above...)
  • If the single voices of a polyphonic patch: No, if e.g. LFO(x) controls pitch of DCO1, the pitch of DCO1 of all voices will follow exactly and entirely it.
  • If Layer: Yes.
Quote
Let X be the same point in one LFO’s phase cycle. Let’s say X is “0 degrees”. Let it be LFO1.
2. In “Free Running” mode, there is no controllable correlation between the 0 degree points of the LFO of each voice. They seem to be random.
Depends on Your syncing. You may sync LFOs to sequencer or MIDI clock (look at LFO "frequencies" above 150). If not synced at all, the single LFOs 0 degree-points will have no correlation to each other (with the restriction of answer to question 3.).
Quote
3. Question: Is the time distance between the 0 degree points of each of these 2 voice’s LFO fixed? i would think it is.
Two or more LFOs running without syncing should keep their phase difference.
Quote
4. I would imagine LFO1’s rate control governs the rate of the LFO of both of these 2 voice’s LFO’s. Correct?
As there is only one LFO(x) for all voices of a single patch, all parameters (destination, amount, waveform, rate, sync) of this LFO will influence all voices of that patch.

A general remark:
When designing sounds, You should do the same as good program designers in other fields, e.g. quite standard software programming.
Never mix goals and requirements with solutions, keep them separate!
  • Start with a descripton (make Yourself as clear as possible, that is) what You want to achieve.
  • If You are done with that - and not earlier! - look for the toolbox (features of Your instrument, that is).

In Your case: Don't press LFOs to do what You want, but use the appropriate modulation source after You have defined Your goal. P'08 features a beautiful and very flexible variety of modulation sources, kinds, and destinations. I have no clue what exactly You try to achieve, but from the little I assume, sequencer or envelope 3 (including its "one shot vs. repeat" facilities) may be a more suitable tool than LFO.
After all, You won't drill a hole with a hammer, if there is a drilling machine...

HTH

Martin



panic

Re: "LFO per voice" for beginners
« Reply #6 on: October 19, 2017, 04:27:45 AM »
Hi Martin,

as I understand it, he doesn't have a specific problem, he is just trying to understand what the different tools in his toolbox can do, and how you operate them (which is useful, otherwise you won't know what to select when you have to solve an actual problem.
In this question, I think he is mainly trying to understand what the consequences are of the fact that your LFOs are per voice, and not global. Therefore, be careful with your answer.

So, each voice has it own LFOs: yes (but they are programmed per layer, not per voice), otherwise it is global.
An important consequence is that when you use a random LFO, the random values will be different for each voice (we recently discussed this in another topic), which can be too chaotic for some applications...
But it allows you to do really cool things, like for example you can have different speeds of the LFO for different voices (when you have the speed of the LFO modulated by for example note number or by another random LFO)

dsetto

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Re: "LFO per voice" for beginners
« Reply #7 on: November 04, 2017, 04:09:13 PM »
MartinM, panic:

Thank you. I appreciate your help very much. Please excuse my late reply. I finally had a chance to test out the scenario we've discussed here.

I think I understand "LFO per voice" when KEY SYNC is engaged. (It's as the manual explains it, and the name implies.) I also understand when CLOCK SYNC is engaged. I believe that means the CLOCK becomes the "tempo" source, overriding LFO 1's frequency.

panic, I've yet to try out thay intriguing way to coordinate each voice's LFO.

dsetto

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Re: "LFO per voice" for beginners
« Reply #8 on: November 04, 2017, 04:18:52 PM »
Let's set aside panic's approach to coordinate all the voices' LFO's.

When KEY SYNC is not engaged, I assume there is no relationship between each voice's LFO. I assume each voice's LFO is free running. And the start points of each voice's LFO is not coordinated with each other.

Is this correct? Is it entirely random? Once the approach panic offered to coordinate the individual voices' LFOs, what keeps them in sync and what pushes them out of sync?

I have read that there is not an official way of syncing the voices' LFOs other than via KEY SYNC engaged, and "key on" coordination.

(With my early level of understanding, I am fine with that. I am not passing judgement. I am trying to understand. In a sense, each voice is like an independent member of an ensemble.)

Thank you, Prophet synthesis scholars.

I have read that there

Thank you.

Re: "LFO per voice" for beginners
« Reply #9 on: November 06, 2017, 01:18:49 AM »
Moinmoin,

dsetto asked:
Quote
When KEY SYNC is not engaged, I assume there is no relationship between each voice's LFO. I assume each voice's LFO is free running. And the start points of each voice's LFO is not coordinated with each other.
The LFOs and Envelopes of the P'08 are managed digitally, but effectively this is true, and that is what matters musically. This behaviour is called polyphonic: Every single voice has its own individual parameters. If modulation circuits are shared between the single voices, this is named by an euphemism called "paraphonic".

Quote
I have read that there is not an official way of syncing the voices' LFOs other than via KEY SYNC engaged, and "key on" coordination.
This is not true: If You look at LFO-speed-values above 150, You will find methods to sync LFOs to sequencer, arpeggiator or (internal or external) MIDI clock.

Quote
...each voice is like an independent member of an ensemble.
This is true by definition for polyphonic voices. You can make them sync, however. And that is a good thing, as it leaves it to the sound programmer, or even more flexible: To the player. To qoute page 1 of P'08 manual:
Quote
Try applying keyboard pressure (aftertouch) and the mod wheel. Many sounds
are fairly simple at first, then come alive when you use the controllers.
Yes: This "coming alive" is modulation.

As always a principle with learning, there are two ways to understanding:
  • If You are familiar with sound synthesis - maybe You are somewhat experienced with monophonic synths or have some physical/theoretical backgrounds - You may use a bottom-up approach: Build a sound by constructing it from its parameters. If You really played with LEGO as a child, You will know what I mean.
  • If You come from keyboard-playing, You could try a top-down approach: Analyze the factory presets and learn how they did it. If You used Your LEGO building and maybe altering the preset models, You will know, what I mean.
A real good guide to synthesizer programmingf on the web and free is here: https://www.soundonsound.com/techniques/synth-secrets

HTH

Martin

panic

Re: "LFO per voice" for beginners
« Reply #10 on: November 07, 2017, 03:06:25 AM »
Is this correct? Is it entirely random? Once the approach panic offered to coordinate the individual voices' LFOs, what keeps them in sync and what pushes them out of sync?
If noting is modulating the LFO rate, they should have no reason to go out of sync. The phase difference of the LFO between the voices should be constant then.
Something you should verify (I don't have a P8 at the moment): I seem to remember having read that the LFOs between the voices have the same starting point (no phase difference) at the moment you freshly load (or reload) your program with free running LFO. However, I think it was about the P12, but perhaps it also is like that with the P8?

This is not true: If You look at LFO-speed-values above 150, You will find methods to sync LFOs to sequencer, arpeggiator or (internal or external) MIDI clock.

Yes, you can sync LFO to clock (internal or midi). In my memory, this still does not allow to sync LFO "between voices", it is as said: bpm (internal or external) just determines LFO rate. But I could be wrong...