I know they sound different, because there are both hard sync and PWM samples in my XS, but what are the other differences between the two?

Re: What’s the difference between hard sync and PW

Joshy - somebody else can probably give you a more in depth description than me, but basically Hard Sync or Oscillator Sync and PWM are two very different methods of analog synthesis.
In Sync you’re locking one Oscillator to another, so it will always follow that Oscillators frequency - much like what’s going on in FM, where you have a Carrier and a Modulator. By locking Oscillator 2 to Oscillator 1 - 2 becomes the Modulator so to speak, and the result is new overtones, that can’t ordinarily be produced in an analog system.
When you incorporate an Envelope to change these overtones it get’s really interesting - and is what made the Prophet V new sounding when it came out. Personally I think the Jupiter 8 has the best Sync sound of any synth I have heard.

PWM stands for Pulse Width Modulation. A Square Wave can have many different widths - a regular Square wave is 50%, meaning the + and the - of the wave are of the same width. If you change that relationship the Wave is called a Pulse Wave and maybe it’s 10/90% which is a Narrow Wave.
On the MiniMoog there is a little selection of static Pulse Waves.
Newer Analogs started incorporating PWM - which means having a modulation source control the pulse width. So having an LFO modulate the PW - you get the relationship between narrow/wide pulse change according to the speed/wave-form of the LFO. This is widely used for big, pulsing pads.

On some of the most advanced analogs you can even do PWM of a Saw Wave - but the sound one is referring to with PWM is that of a Square/Pulse wave being modulated.

If you can get hold of a Kurzweil K-series ( which sell for cheap now ) you can check it all out - and you will see how different those two things are, and why it is impossible to ‘sample’ that. This is one of the main reasons why Virtual Analog is preferred over sample based machines for synthy sounds - there is just a whole world of analog sounds you can’t even get close to using a sample based system.

Hope this gives you a small introduction to this - but you really have to hear it and turn the knobs to fully appreciate it. One of my things to do for fun, is in fact experimenting with especially Sync on my Super Jupiter. It doesn’t matter where you turn the knobs - it all sounds great, but changes infinitely as you go. And I think that is the hallmark of a good analog - it is impossible to get it to make a bad or unusable sound.


-Kim

Re: What’s the difference between hard sync and PW

Click for Pulse Width Modulation explanation

Click for Hard/soft sync explanation

Yamaha’s plug-in board PLG150-AN does both..... 


Brian Cowell
CUNKA - Audio Reality -

Re: What’s the difference between hard sync and PW

Thanks guies for the explanations.  The XS has the best hard sync and PWM samples I’ve ever heard, and that was one of the main reasons I got it.  I know the difference in the sound, but I didn’t know the technical differences between the two.  I’m still not sure I understand how an LFO can modulate a pulse width.  Does it take two oscelators to do it?

Re: What’s the difference between hard sync and PW

< Does it take two oscelators to do it?>

No - the LFO ( which is actually also an Oscillator ) can modulate the Pulse Width of just one Oscillator, or several if you want.
Modulating one Osc positive and the other Negative can even further widen the effect.

-Kim

Re: What’s the difference between hard sync and PW

I’ll echo Kim about sample-playback not cutting it when it comes to sync. Virtual analog really doesn’t do it either. Like the Super Jupiter mentioned above, my JX-8P has an AMAZING hard sync lead sound that I’ll never get tired of and that nothing else comes close to duplicating. From a muted, subdued tone at the lowest velocity to an absolute explosion of overtones when you hit the key hard, there are at least 5 or 6 distinct tonal gradations in between. And that is not mentioning the ever evolving decay sounds for each of those velocities when you hold a note. It’s a double-edged sword though because once you play a ‘real’ hard sync sound on one of those keyboards, anything else really isn’t the same!

Re: What’s the difference between hard sync and PW

I’m still not sure I understand how an LFO can modulate a pulse width.

An analog synth generally will have a pulse width control (knob) on it.  You turn it all the way one way, you get a square wave.  As you turn the PW knob, the pulse width narrows and the sound changes.  Now if you turn the knob back and forth rhythmically, the pulse width changes from wider to narrower and back over and over.  That’s all the LFO is doing in PWM.  You can hear it in the XS’s PWM samples.  You can also observe what different pulse widths sound like by going through waveforms 1037 through 1043.  1037-1039 are 10% pulse waves, 1040-1041 are 25% pulse waves, and 1042-1043 are 50% pulse (aka square) waves.

Re: What’s the difference between hard sync and PW

Thanks guies!  I’ll have a look at those waveforms.  If I can figure out how to get the LFO to crossfade between elements, I may be able to get a convincing PWM effect using the waveforms mensioned above.  That’s one thing wave sequencing would be good for. 

So, if you modulate one oscelator with another like you could on the Prophet 5, is that a form of FM, or what is it?

Re: What’s the difference between hard sync and PW

Wave sequencing would give a jerky version of PWM.  Usually PWM is done with a sine or triangle LFO so it transitions smoothly.

So, if you modulate one oscelator with another like you could on the Prophet 5, is that a form of FM, or what is it?

It depends on the type of modulation.  If one oscillator is modulating the pitch (frequency) of the other, that is FM or cross modulation.  If one oscillator modulates the amplitude of the other, that’s AM or ring modulation.  IIRC the Prophet can also do filter FM, which is like oscillator FM except the oscillator modulates the filter cutoff instead of the 2nd oscillator.

Imagine you have a synth where one oscillator also functions as an LFO (Minimoog), or one with an LFO that can go up into the audio range (Prophet).  If you set it to modulate pitch, at LFO frequencies you would get vibrato, and at audio frequencies you get FM.  Set it to modulate amplitude, you would get tremolo at LFO frequencies and ring modulation at audio frequencies.  Modulate filter cutoff and you get wah-wah at LFO frequencies and filter FM at audio frequencies.