The sweeping sound was done by someone else taking a Yamaha DX keyboard and sampling in a portamento. You can see the process here:

https://www.youtube.com/watch?v=IAvIUAPb7Qo

He's using sine (which is a default FM Performance for MODX) and adding portamento. You don't have to sample it. This made it easier for him to just press a single key and have repeatable results.

Here's the full cover:

https://www.youtube.com/watch?v=G4z1PHk_P5o

The other sounds aren't broken down. Just throwing out there that looking into what others do in their covers may help. I would usually search for the song title and "yamaha" in Youtube to find any Yamaha keyboard playing this cover as there is a lot of overlap between various products over the years.

Hi Jason,

Thanks for the tip.

I used the Init FM performance and then mucked around on the Pitch Envelope page - see screenshot.

I couldn't seem to get it to work well by pressing the higher note and then letting it rise to that - I seem to have to play the lower note and then pull off when I get to the right high note. Not perfect but I need to understand the PEG controls a bit better maybe.

I guess it would be easier to know something about synthesis rather than spending hours searching for the sounds...

There are two things in play here. One is you are trying to duplicate a specific sound. The other is you are learning about synthesis. It is highly recommended that you don't make the "search" for sounds just a time consuming task... while you are searching, when you find anything interesting, even if only remotely related to your specific goal, stop and spend some time exploring what is going on.

You are looking for something that can be reproduced via "Portamento" or "Pitch EG", or perhaps other ways... if you are searching through sounds, and discover a sound that is using Portamento or Pitch EG, or an LFO or Motion Sequene to influence the pitch behavior, stop and see if you can find out how this is being accomplished. It's sort of a targeted learning side-trip. You may not ever find the exact sound you are looking for, but by following up on the ways pitch movement is being addressed in the Factory sound set, you will combine the two tasks (searching and learning) in a meaningful way.

I am guessing that I need to start with an init performance and search for the appropriate waveforms and then apply the filters/effects?

Ultimately, this is the workflow you want to get to... eventually. Take your time. It is certainly going to be apart of that second thing: Learning about synthesis. But while you are searching through waveforms and/or Performances for the kind of thing you wish to work with, consider directing your search by targeting a specific area. In your case, one of the things is the pitch movement (which is the starting point).

If anyone can steer me in the right direction?

When approaching changing the pitch upon Key On, you have several methods, among them: "Portamento" -which lets you slide between a source and target pitch controlling distance, speed and time, and you have the "Pitch EG" -which lets you control the behavior of the pitch over time and additionally be influenced by Key On Velocity and even influence pitch beyond Key Off.

You must determine which will work best for you, in what you are trying to accomplish and how you need to apply it. Does it need to a rapid repeated thing or does it need to happen over a set amount of measures/beats, etc.

Portamento is programmable as to the behavior. When doing most acoustic instrument emulation, the distances involved are short and the concentration is to move to the pitch of the target Key. When doing electronic emulation, the distances can be several octaves and the note that triggers the movement does not necessarily have to be the pitch you are targeting (this is where the direction and distance of movement is the priority).

When working with portamento you will see that you can set a Time and Rate parameter which determines how the function behaves. There are two different types (Time1/Rate1 and Time2/Rate2), explore them.

Determine the distance of pitch change you desire, and how quickly the pitch changes.
If you do not want to hear the start point... as you may notice that when Portamento is involved, often the direction of movement is determined by the previous note played. So if you are looking to do upward movement each time, you might have to trigger the start note to RESET the desired upward movement.

There are several ways to silence that lower note that RESETs the start of portamento. Within the synth engine you have multiple BREAK POINTS. These allow you to control the Output Level of each Element/Operator as you move across the keyboard.

For example, if you want to press a low key but not have that key make a sound, you could use these BREAK POINT parameters to reduce their output levels to eliminate them from sounding. In the FM-X engine you will find access to these parameters per Operator "OP1-OP8" >"Level" screen. You can set a Break Point across the keyboard and then scale the Output Level of the selected Operator as you go above and below that Break Point. The Curve can be adjusted as to how severe the change.
In the AWM2 engine you will find access to the Break Point parameters per Element "Elem1-Elem8" > "Amplitude" > "Scale"

Pitch EG
When using the Pitch Envelope Generator (PEG) to control the behavior, you can setup to have the pitch start from below and arrive at the pitch of the Key you are pressing or you can have it move away from the pitch of the Key you press.

The x-axis (left-to-right) is like a keyboard and goes low-to-high.
The y-axis (up-and-down) is your pitch variance.

If you move your cursor to the LEVEL parameter for "Initial" and make that a negative value, then you can fashion a pitch variance that rises to the pitch of the Key you press.

When the "Initial" Level is negative, the pitch begins below the centerline that represents normal pitch.

Thanks Bad Mister!

Great advice as usual!