Roland JX3P and PWM

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Re: Roland JX3P and PWM

Post by tertiumsquid » Sat Mar 21, 2015 8:21 pm

DesolationBlvd wrote: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.
I see what you mean now - I did notice that the top half of PWM on my 3P starts adding in a second pulse (and therefore an octave up). In practice though, you could just modulate from 20% to 50% at half the speed. I can't say I've used a synth with regular PWM, so I don't know about amplitude loss.

I still have to say - if regular PWM and sync-PWM look pretty much the same on a scope, how can they sound different? Seems to me that people are hearing inherent differences between two different synths than between the two different types of technology.

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Re: Roland JX3P and PWM

Post by madtheory » Sun Mar 22, 2015 12:47 pm

This is definitely not a case of hearing something that cannot be measured, especially because DesolationBlvd is making a very viable description of the wave theory involved! Seems to me that someone is not using the 'scope properly, for example it's easy to ignore slight level variations over time on older/ analogue 'scopes (which a lot of people use for audio work because they're fine for that and inexpensive). Similarly, it can be hard to get the waveform display to be stable because the 'scope doesn't trigger very well.

So instead of someone's say so about what they claim to have seen on a 'scope, it would be much better to have actual measurements and pictures along with a description of how the observations and measurements were taken. That way, if there are methodological flaws they'll be obvious. So will any confirmation bias. That's how science works :)

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Re: Roland JX3P and PWM

Post by max badwan » Tue Mar 24, 2015 10:44 am

I know I'd seen a vid somewhere, demonstrating PWM via sync, with an oscilloscope, and here it is...

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Re: Roland JX3P and PWM

Post by madtheory » Tue Mar 24, 2015 1:00 pm

That's an excellent demo. So clear. And funny :) I think the same technique is possible on the Roland JV synths. I must dust off the JV-1080!

So I guess anyone who thinks PWM via sync sounds different to PWM via LFO is suffering from a perception bias. The proof of this would be a blind AB test. If you don't know how the PWM is made, all you have to go on is what you hear.

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Re: Roland JX3P and PWM

Post by meatballfulton » Tue Mar 24, 2015 4:31 pm

Wow, you're making me all misty eyed about my old SQ80.
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Re: Roland JX3P and PWM

Post by pflosi » Tue Mar 24, 2015 4:53 pm

madtheory wrote:Seems to me that someone is not using the 'scope properly, for example it's easy to ignore slight level variations over time on older/ analogue 'scopes (which a lot of people use for audio work because they're fine for that and inexpensive).
I don't think so mate. :D It also sounds the exact same and it's also the same in theory. In addition to looking the same on a scope.
madtheory wrote:So I guess anyone who thinks PWM via sync sounds different to PWM via LFO is suffering from a perception bias.
See? That's much better ;) Also, you still need an LFO with the sync method.
tertiumsquid wrote:
DesolationBlvd wrote: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.
I see what you mean now - I did notice that the top half of PWM on my 3P starts adding in a second pulse (and therefore an octave up). In practice though, you could just modulate from 20% to 50% at half the speed. I can't say I've used a synth with regular PWM, so I don't know about amplitude loss.

I still have to say - if regular PWM and sync-PWM look pretty much the same on a scope, how can they sound different? Seems to me that people are hearing inherent differences between two different synths than between the two different types of technology.
Regarding the two points from DesolationBlvd that I've just written off as "wrong" before, some clarifications.

1) It's true that you only get "silence" in one direction, when the slave is more than two octaves down compared to the master. But you do get it there and that means you can emulate the classic PWM "fade in/out" effect (if you want).

2) This only applies (more or less-ish) when both oscs are the same frequency. As written before, two octaves down on the slave gives silence, one octave up "folds" in the first second-order pulse. Thus, as also mentioned earlier, if you tune the slave down half an octave (i.e. 6 to 7 steps), you get the widest range. Which is easily "20-80%".

Note that I'm not at all talking about the specifics of the JX3P. Anywhere in the thread.

I also hope I didn't confuse anything now, writing it all up from my office chair right now, with no synth in sight.

I've tested this extensively on my A6 that can do both "methods", using the same LFO and so on, and it sounds and looks exactly, precisely, 100%, on the spot, the exact same. And theory tells us that that's right as well.

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Re: Roland JX3P and PWM

Post by madtheory » Tue Mar 24, 2015 7:37 pm

pflosi wrote:I don't think so mate. :D It also sounds the exact same and it's also the same in theory. In addition to looking the same on a scope.
Niether do I, now that I've seen it demonstrated on a 'scope with a good methodology (and a good 'scope). See? Evidence is always better than opinion. Now if we can teach that to Hugo76, we'll be making progress. LOL!

O ya, the guy used his hand as the LFO :p

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Re: Roland JX3P and PWM

Post by DesolationBlvd » Tue Mar 24, 2015 11:58 pm

After watching the SQ-80 demo of PWM by sync, I stand corrected.

It still takes up an oscillator, so you can't do PWM + detuned saw unless you have a third oscillator. On the JX, it's best to just use detuned saws if the end result you want is a rich pad.

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Re: Roland JX3P and PWM

Post by pflosi » Wed Mar 25, 2015 11:09 am

Yes, it's not very practical (you lose an osc, bit fiddly to dial in, etc.), but the discussion has long been about the fact that some people didn't wanna believe that it's t h e s a m e.

As written in the other thread, it's funny how PWM was established to "synthesize" a two-osc beating sound with one osc, but on the other hand you can also "synthesize" PWM with two oscs and sync :)
madtheory wrote:Niether do I, now that I've seen it demonstrated on a 'scope with a good methodology (and a good 'scope). See? Evidence is always better than opinion. Now if we can teach that to Hugo76, we'll be making progress. LOL!
Yeah, it was a bit unfortunate that I saw both your replies at once... :thumbright: but I was sure you'd get my cheekyness ;)

And :thumbleft: :drinks: :lol: on the second point! :D

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Re: Roland JX3P and PWM

Post by madtheory » Wed Mar 25, 2015 1:29 pm

:thumbleft: :drinks: :lol:

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Re: Roland JX3P and PWM

Post by tertiumsquid » Thu Mar 26, 2015 6:38 pm

Hah thanks guys, it's nice to see everyone come to an agreement in the end!

Now if only I had a synth with normal PWM, then I could've proven it myself. Guess that just means I need to buy more synths!

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Re: Roland JX3P and PWM

Post by Bitexion » Fri Mar 27, 2015 2:58 am

Yeah go and BUY more synths so you can prove a point in this silly thread! Spend your money faster!

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Re: Roland JX3P and PWM

Post by tertiumsquid » Sat Mar 28, 2015 1:20 am

Bitexion wrote:Yeah go and BUY more synths so you can prove a point in this silly thread! Spend your money faster!
Your devilish avatar compels me.

Must... Buy.... Synths......

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Re: Roland JX3P and PWM

Post by Automatic Gainsay » Sat Mar 28, 2015 2:12 am

We all love PWM because it's a cool sound.
But it's an effect, not a synthesis too. Lots of synths don't have it. Many vintage synths only had it as an apology for single oscillators. If you want it, seek a synth that has it. If you have a synth that doesn't have it... use the synth for what it does. PWM is not a synthesis tool. If you need it, seek it... but don't expect it.
The fact that the JX3P has so many functions other polysynths (especially Rolands) don't have should be more important.
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Re: Roland JX3P and PWM

Post by Bitexion » Sat Mar 28, 2015 2:42 am

I love that it makes lead sounds sound like BAAAAOOOAAAAAOOOOAAAAOOOOAAAAAOOO
And makes bass sound like BWWWWWWWOOOOOOOWWWWWOOOOOOWWWWWWWWW

And that pretty much every good C64 song uses a PWM lead sound.

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