One thing not fully explained in the OHM is the use of Zxx macros for filtering sample-based instruments. For those new to tracking with MPT, let me clarify after some testing...
When creating a sample-based instrument in the Instruments tab, you have the option to set the instrument's default cutoff and filter mode. For example, you can take a sample, set its mode to Hi-Pass (the default is always Lo-Pass). You can then adjust the cutoff range to "shelf" the sound to that side if you check the box next to the cutoff option.
Take a piano sample. If you set the mode to HP, and set the cutoff to the lowest setting (for MPT it's 130 Hz -- a bass even lower than most kick drums), the HP shelf will extend all the way from the highest frequencies down to the lowest). Move the cutoff slider to the right, and you'll notice more of the lower frequencies are "cut off" (hence the term). At its highest setting, only the highest frequencies are left, making the piano sound tinny and thin. The opposite is true if you set the mode to Lo-Pass -- the higher frequencies are cut off as you move the slider LEFT. You'll only hear the bassest notes in the piano sound if those frequencies lie BELOW the cutoff range (remember, that 440 Hz for example is middle A). Actually the cutoff shelf is not sharp it's smooth -- altho an option for that would be nice. The graphic below is in the OHM to remind you of the various values and their effect on each frequency range.
It helps to imagine that each box in the image is a set of Equalizer sliders that filter out various frequencies.
The top pair of boxes is the shelf effect you get when you set the Filter Mode, but not the Cutoff frequency. The other pairs of boxes show the effect of different settings based on Filter Mode (Lo-Pass or Hi-Pass) and the extremes in Cutoff values and Resonance values.
You can alter both the mode and the cutoff range using SFx assignments and Zxx commands for modifying a sample's audio during playback. SF0 is MPT's default assignment, and its designated for the Filter Cutoff. You can assign SF1 to the Filter Mode in the Macro Manager dialog (accessible from the Patterns page), but the values to use have never been made clear. The range for the Cutoff slider is from Z00 to Z7F. The Filter Mode is set to Lo-Pass at Z00 (up to Z0F), and Hi-Pass at Z10 (or higher).
In order to extract only the highest frequencies of a sample, set the Filter Cutoff (default: SF0) to about 1760 Hz or higher, after setting the Filter Mode to Hi-Pass, like this:
... .. .. SF1 You've already assigned to Filter Mode in the Macro ManagerIf you want to use the Lo-Pass Mode, set the value in the second row to Z00. Then all notes whose frequencies are ABOVE ZC0 (about 1760 Hz) will be cutoff in this example.
... .. .. Z10 Same as setting the Filter Mode in the Instruments page to Hi-Pass
... .. .. SF0 Default setting for Filter Cutoff
C-5 01 .. ZC0 Same as setting the Filter Cutoff to approx. 1760 Hz.in the Instruments page
Of course you can interpolate cutoff values to create a frequency shift for any note, a technique esp. useful in today's music.
ONE IMPORTANT CAVEAT: Calling a note event (note and/or instrument) WITHOUT a Zxx command resets the filter to the instrument's default settings. Therefore, the note event must be called at the first Zxx command AFTER the SFx command for the Cutoff. In the above example, if C-5 (with or without the instrument) was called in the row AFTER the ZC0 command was passed, the ZC0 cutoff value would not have been applied to the note, instead reverting back to the instrument's assignment found in the Instruments page. (The ZC0 would still have been processed on any notes still playing in the channel.)
Keep in mind that when these commands are encountered in playback, the changes to these settings are not reflected in the Instruments page, in case you're trying to monitor the settings. (The Instruments page will always show the instrument's default settings, no matter what is changed during playback.)
Don't forget that you can also use a higher frequency range by setting the Extended Filter Range checkbox in the Song Properties dialog. This allows your maximum cutoff to extend up to about 10,000 Hz rather than MPT's default 5,000 Hz. (The Zxx range is still set from Z00 to Z7F, but is translated for the new frequency range.)
The information in this thread will find its way into the next build of the OHM, but this is placed here for reference in case questions arise before then. If anyone else learns more info on this subject, please include it in this thread (even as MPT evolves).