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Roland JX3P and PWM

Posted: Sat Feb 14, 2015 8:14 am
by tertiumsquid
Hi all, I'm just curious about something - I've read many opinions about the Roland JX3P, and I very often hear that it "does not have real PWM". This confuses me, as I own one, and it's not hard to modulate the pulse width with either the LFO or envelope - Set DCO mix to 2 only, set CrossMod to Sync, and rotate the Tune knob to sweep pulse width, or set the LFO or Envelope to modulate the pitch of Dco2, which modulates pulse width. I've never seen any other mention of this in any forums though - it's written in the manual though!

So, did everyone just ignore the instruction manual, or is there more to "real PWM" than what I'm doing here?

Re: Roland JX3P and PWM

Posted: Sat Feb 14, 2015 10:15 am
by commodorejohn
To many people it doesn't sound quite the same, as much as it should theoretically work out that way. Whether you lend it any credence or not, some of us just don't hear it as "real" PWM.

Re: Roland JX3P and PWM

Posted: Sat Feb 14, 2015 3:40 pm
by pflosi
Didn't we have this just recently?

It's "synthesizing" PWM with osc sync. You lose the second osc that way. Any synth with two (square) oscs and sync can do it. When you understand sync, it's totally obvious that this must happen.

And John, it's just a matter of dialing it in precisely and it will sound exactly the same as "real" PWM. An oscilloscope helps a lot.

Re: Roland JX3P and PWM

Posted: Sat Feb 14, 2015 3:43 pm
by pflosi
The other discussion about this that I meant was in the JX3P vs Polysix thread, starting here:

http://www.vintagesynth.com/forum/viewt ... 30#p741274

Re: Roland JX3P and PWM

Posted: Sat Feb 14, 2015 6:23 pm
by commodorejohn
Personally, if I have to use an oscilliscope to get it to sound right, I'll just use a synth with actual PWM instead.

Re: Roland JX3P and PWM

Posted: Sun Feb 15, 2015 7:59 am
by max badwan
commodorejohn wrote:Personally, if I have to use an oscilliscope to get it to sound right, I'll just use a synth with actual PWM instead.
I'm curious, just what is "actual" PWM in your considered opinion? PWM through sync is "actually" PWM, just without an "actual" knob.

Re: Roland JX3P and PWM

Posted: Sun Feb 15, 2015 8:11 am
by commodorejohn
As I've said, it doesn't sound the same to me. You can accept that or dismiss it, but as far as I'm concerned they're not functional equivalents.

Re: Roland JX3P and PWM

Posted: Sun Feb 15, 2015 10:44 am
by max badwan
commodorejohn wrote:As I've said, it doesn't sound the same to me. You can accept that or dismiss it, but as far as I'm concerned they're not functional equivalents.
Fair enough. Personally, I don't expect anything to do everything. I'm habitually trying to push boundaries, in more ways than one.

Re: Roland JX3P and PWM

Posted: Sun Feb 15, 2015 10:53 am
by pflosi
So what now, when you use an oscilloscope to get it to "sound right", does it sound "the same" or not?

I'm still baffled that you insist that it sounds differently? What about it is not functionally equivalent with "normal" PWM? Nobody says you have to use it, that's a different topic...

Re: Roland JX3P and PWM

Posted: Mon Feb 16, 2015 12:37 am
by commodorejohn
pflosi wrote:So what now, when you use an oscilloscope to get it to "sound right", does it sound "the same" or not?
That was sarcasm. I don't actually use an oscilliscope because it's a million times simpler to just use a synthesizer with proper pulse-width modulation so that I can have the oscillators tuned separately and don't have to d**k around for forever trying to make it sound like I want it to.
I'm still baffled that you insist that it sounds differently? What about it is not functionally equivalent with "normal" PWM? Nobody says you have to use it, that's a different topic...
I have no idea why it sounds different, it just does. Considering that this is a site where people talk quite seriously about the unique special qualities of just about every permutation of every functional block of every classic synthesizer, I'm kind of surprised that you find the idea this baffling.

Re: Roland JX3P and PWM

Posted: Mon Feb 16, 2015 2:00 pm
by pflosi
commodorejohn wrote:
pflosi wrote:So what now, when you use an oscilloscope to get it to "sound right", does it sound "the same" or not?
That was sarcasm. I don't actually use an oscilliscope because it's a million times simpler to just use a synthesizer with proper pulse-width modulation so that I can have the oscillators tuned separately and don't have to d**k around for forever trying to make it sound like I want it to.
I'm still baffled that you insist that it sounds differently? What about it is not functionally equivalent with "normal" PWM? Nobody says you have to use it, that's a different topic...
I have no idea why it sounds different, it just does. Considering that this is a site where people talk quite seriously about the unique special qualities of just about every permutation of every functional block of every classic synthesizer, I'm kind of surprised that you find the idea this baffling.
Well... Yeah I totally agree that it's more useful to have and use a synth with "actual" PWM... But for the sake of theory and the argument: when you have an oscilloscope to fine tune everything, it will sound e x a c t l y the same (it's possible without one but it helps). Certainly you always had too much modulation when you've tried (as also said in the other thread, you get the widest possible range with the modulator tuned half an octave down).

As said in the other thread: it's the same as PWM in theory, it looks like PWM on a scope, and it sounds like PWM. It must be PWM?

I'm surprised that on a "site where people talk quite seriously about the unique special qualities of just about every permutation of every functional block of every classic synthesizer" this is so hard to accept?

Re: Roland JX3P and PWM

Posted: Thu Feb 26, 2015 4:02 pm
by DesolationBlvd
There are two aspects of sync-PWM making it sound subtly different from regular PWM.

First, in regular PWM, the amplitude decreases towards half as you approach 0/100% pulse width. In sync-PWM, there is no amplitude loss as you approach 0/100% pulse width.

Second, you can't get the sound of modulating from, say, 20% to 80% pulse width when using sync to generate PWM. The other half of the range is the sync sound, not the PWM sound, as the pitch is raised from the original.

Re: Roland JX3P and PWM

Posted: Thu Feb 26, 2015 5:53 pm
by pflosi
Sorry, but you're wrong on both accounts :roll:

Re: Roland JX3P and PWM

Posted: Sat Feb 28, 2015 5:02 pm
by Jinsai
I have a JX-3P (with the KiwiTechnics mod). I tried (before and after the mod was installed) to emulate PWM as has been described.

In theory, it should work. In practice, it sounds like oscillator sync. I suppose one could try this same emulation trick on any synth with sync AND PWM.

Rather than focusing on what the JX-3P can't do, I try to use it for the things it excels at - being a budget Jupiter!

Re: Roland JX3P and PWM

Posted: Sat Feb 28, 2015 5:08 pm
by pflosi
For god's sake :facepalm: Just because you geniuses cannot dial it in, it doesn't mean that it doesn't work.