Automation item with Sine LFO

[abnegative]

When I create an automation item and open automation item properties to set the LFO shape to Sine, the envelope looks strange at first. It looks like the sine wave wants to be at half amplitude, then full, then half again; so when I loop the shape, I get a weird "sine" wave.

To make the shape look normal, I always have to first set the Phase to 25. Is this expected?

original post: https://forum.cockos.com/showthread.php?p=2739422

[akademie]

Confirming! (v7.05+dev1113, x86, Windows10)
There is a wrong (opposite) curve when going from center to max amplitude at the begining of the item and when negative amplitude back to final center point.
(multiple cycles inside the item are correct)

The shifting phase can workaround it to look correct, but then the automation values do not start at center (if needed).

[mindlessgenius]

Edit: I have to correct myself, confirmed for REAPER 7.06 x86_64, Fedora 39.

Steps to reproduce:
- Insert automation item
- set LFO shape to 'sine'
- loop automation item
- see the curve is not continuous

[mindlessgenius]

Possibly related:

I just tried to make a workaround.

• I created an automation item of twice the length needed,
• set it to two cycles,
• trimmed away the inversed start and end segments
• and copied the proper parts of the curves with snap enabled, and Ctrl+Left Drag from a time selection:

But when I tried to glue it in order to make it loop seamlessly this happened:

Difference:


Similarly with four cycles and just trimming to a single sine cycle, before glue:

Glued:

Difference:


Full imgur post:https://imgur.com/a/dFyhEft

[akademie]

^^^^^ Nice proof with those difference pics, mindlessgenius.
Thank you for contribution to this bug report.

[schwa]

Yeah the problem is that REAPER has a sine/cosine envelope point shape, labeled "slow start/end", but not a native half-sine shape, actually we'd need two half-sine shapes. We can approximate these shapes using the same logic that gets applied when you trim an envelope, but as post #4 shows, it's an approximation. We'll think about the best way to handle this.

[mindlessgenius]

Does that account for the LFO generator as well?
For glueing/manually drawn curves this seems reasonable, but for something labelled "Sine" in the automation item properties it is somewhat odd to have a different function on both ends.

[abnegative]

Originally Posted by schwa

Yeah the problem is that REAPER has a sine/cosine envelope point shape, labeled "slow start/end", but not a native half-sine shape, actually we'd need two half-sine shapes. We can approximate these shapes using the same logic that gets applied when you trim an envelope, but as post #4 shows, it's an approximation. We'll think about the best way to handle this.

Thanks, Schwa!

If you start making code changes for this, it may make sense to address this one at the same time: https://forum.cockos.com/showthread.php?t=285804