Today, Rewbs, Atlantis and I were having a nice discussion.
Based on the bug .45 Plugin levels screw up DXM plugin
, we've got into a discussion on why it happened and such. This in particulair because Rewbs didn't seem to have this problem.
As it turned out, its all about the pre-amp value. In a past, a few comparisments gave as result that setting the preamp to max with a global volume of 64 creates very good circumstances to make music, as the levels would be at an ideal situation. The thing however is, that the way MPT handles the preamp levels and global volume, becomes an issue in certain situations. One of the issues is the bug, described above.
In order to go in-depth about how and why, first a few facts.
When you apply a DirectX plugin, Modplug will send the sound to the plugin, which does calculations, and then send its output back to modplug.
This is also the case with VST plugins, except that the DirectX plugin architecture does not allow the sound to go past 100% clipping point. So what basically happens, is that the sound inside of the plugin is being capped to produce 100% volume at max, where in a VST plugin, the volume can rise above it without causing clipping.
The reason behind this has everythign to do with both the plugin levels aswell as the pre-amp settings.
As you may know, we started with Original Plugin levels. This resulted in having volume twice as loud as intended, which was caused by a bug in the code. Pre-amp was actually there to bypass that bug. RC1 was going to fix this, but due to a typo it didn't do it 2x but 16x.
RC2 was going to fix it for good and make it as it supposed to be.
This is what RC2 plugin levels do:
MPT has a sample with a given volume. This sample is being amplified by the pre-amp setting, to alter the volume of the sample. It is then being send through the effects plugin. When it comes out the effects plugin, the Global volume will alter the end volume.
As you can see, its now easy to explain why the bug occurs.
I had the pre-amp at max with a global volume of 64.
With a vst, this happens:
sample is being amplified to extreme values, the vst does calculations with it, and the global volume reduces it back to normal values.
However, with DX plugins the following happens:
sample is being amplified to extrene values, the dx plugin does calculations, detects the output to be clipping like madness, and therefor reducing the output in such way that it sounds all destorted and such (eg. compressing) and the global volume then reduces it back to normal volume, except that due to the dx plugin, its not normal anymore.
With this knowledge, Rewbs, Atlantis and I were doing some tests.
It seems that a Pre-Amp value of about 33% (to 33.3333%) in conjunction to a global volume of 128 gets the perfect non-clipping range to make your music in.
For that reason, I recommend to use a Pre-Amp value of 33% at all times, with a combination of a global volume of 128.
Rewbs will make an RC3 plugin levels setting that will override the pre-amp value to 33% (the exact value is yet unknown, but it will result in a perfect 0.0 clip level.