Add Granular Pitch Shifter effect

[LostRobotMusic]

Finally, after twenty year-sized years, LMMS has a pitch shifter that isn't garbage. Yay!

The GUI was created by thismoon.

Almost all granular pitch shifters out there make the same fundamental mistake, that being the use of equal-gain fades instead of equal-power fades. It is for this reason that this type of pitch shifter is infamous for only being useful for sound design purposes rather than high-quality CPU-efficient realtime pitch shifting. It's a tad sad to watch many developers of these pitch shifters even go as far as to use autocorrelation algorithms and the like to try to correlate the grains, in a desperate attempt to help their equal-gain fades sound a bit less awful, with... varying levels of success... usually not much.

This pitch shifter doesn't make those fundamental mistakes. By default, the fades used in this plugin are equal-power. I explain why these are the correct fades in this video here: https://www.youtube.com/watch?v=-5cB3rec2T0

Along with this comes several features to help with ensuring the grains are uncorrelated so this grain shape is always optimal. The simplest and subtlest way to achieve this is to use a very tiny amount of "Spray" which slightly randomizes the positions at which the grains are started from in the delay buffer. This is done by default.

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This pitch shifter comes with a "prefilter" lowpass which almost entirely eliminates any aliasing generated by the pitch shifting, without needing to resort to oversampling. This is possible by applying the filter before the pitch shifting, slightly below the frequency that will be shifted up to the nyquist frequency.

While most pitch shifters have a fixed amount of latency, this one (optionally) dynamically changes its latency to the absolute lowest it can possibly be for your current settings. This can be overridden by increasing the latency knob, which will set a minimum latency requirement. This also controls the delay length of the feedback, which allows shifting the audio repeatedly as it is fed back through the delay buffer for infinity.

For those who would like to use this pitch shifter for more creative sound design purposes, the Random section covers this very nicely. Spray can randomize the read locations of each grain up to quite a long while back in time. Jitter randomizes the pitch of each grain, while Twitch randomizes when these grains are created. The three of these together allow particularly satisfying buffer-shifting sounds, which will always sound perfectly clean due to the long equal-power fades in use.

The Density knob allows significantly increasing how often grains are created, which combined with the Random knobs can result in a sound similar to Paulstretch, but without the stretch. So just Paul, I suppose.

I added built-in documentation for the plugin so users can understand how to use it.

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I have a quick demo of the plugin here (though it and its UI are a tad out of date):
https://www.youtube.com/watch?v=_8am4hjL-Tc

[Rossmaxx]

Just so you know, valuebuffer is on it's way out in #7297 . You don't need to worry for now. I'll intervene for fixing this PR up if that one gets merged.

[Rossmaxx]

Just some minor stuff i came across.

[Gabrielxd195]

A small graphic detail is that there are inconsistencies in the letters, for example: "range" and "second" are in lowercase, when it should be "Range" and "Second"; While "LATENCY", TWITCH, DENSITY, SHAPE, PITCH, SPRAY, JITTER, SIZZE, GLIDE, FDBK and FDBK are capitalized. I don't know if they are doing this on purpose, but I think it would be better if each word starts in capital letters, like: "Stereo", "Prefilter". To make it more pleasing to the eye. Greetings

(Google Translate)

[Rossmaxx]

Now that you said it. I've noticed it just now. It would be better to keep the abbreviations (RND, FDBK and co) the same and apply changes to the rest, to bring in some contrast for abbreviated names.

[tresf]

We don't yet have a style guideline for acceptance of plugins. This is largely due to the fact that we've historically allowed theming of plugins and those themes make use of the background image for labels.

At a glance, this plugin uses:

• Title case for the sections
• CAPS for the knobs

SFXR uses this same technique.

The only inconsistencies I can find:

• RND: may be changed to Rand
• 5 seconds: We would write this as 5 Seconds elsewhere
• range: Probably should be Range to be consistent with other sections.

[sakertooth]

Tested it, cool plugin 👍

[sakertooth]

After these few changes I think its good to go 👍 (on my end at least)

[LostRobotMusic]

[LostRobotMusic]

I added a 7 Hz 1-pole highpass to prevent DC offset buildups in the feedback loop. I also added a very CPU-efficient safety saturator I made to guarantee the feedback is always safe. With a sufficiently low input volume (below +24 dBFS), all it needs is an abs and a correctly predicted branch.

This plugin is 100% ready for merge as far as I can tell, but it needs one more approval first.

[Rossmaxx]

Here it comes