AudioEffectPitchShift: Fix distortion when pitch is 1.0

[pattlebass]

Fixes #96510

I believe the issue was some kind of double to float precision error.
It only occurred when changing the pitch_scale to a value different from 1.0 and then back to 1.0 (from GDScript or the inspector), but not by default or when hard-coding it to 1.0 in C++.

The project I used for testing:
pitch-shift-bug.zip
Toggling the effect on and off should no longer yield any audible difference.

[akien-mga]

Thanks!

[JUSTCAMH]

I believe this fix won't have the intended effect. If you were to setup a script to linearly transition from pitch shift 1.1f to 1.0f, then you'd hear audible popping as the pitch shift effect turns itself off at pitch = 1.0. When I submitted the attached issue, I tried manually turning off the pitch shift effect when the pitch is 1.0, and this had a very noticeable popping to it.

We should fix the core problem (of this supposed double to float precision error) so that you can smoothly transition pitches without any popping or distortion.

[3lis4]

Thank you all for your time on this issue.
@JUSTCAMH Do you know if it's planned somewhere to fix the core issue ?

This issue exists since a long time but maybe wasn't properly fixed, see #20198. They also thought about disabling the effect for 1.0 value, but call it "a cheap workaround" :

As soon as you activate the effect audio gets processed by an additional algorithm which transforms the original sound; regardless of the effect’s configuration, the input is changed.
A cheap workaround would be to bypass the effect as long as the value is 1.

It's probably good to have this workaround for now, but it shouldn't prevent from fixing the core issue later on.