0001671: 'Z7F' cutoff commands don't apply properly for OPL instruments unless filter envelope is enabled

ID	Project	Category	View Status	Date Submitted	Last Update

0001671	OpenMPT	Playback Compatibility	public	2023-02-28 22:01	2023-03-01 18:52

Reporter	teimoso	Assigned To	Saga Musix
Priority	normal	Severity	minor	Reproducibility	always
Status	resolved	Resolution	fixed
Platform	x64	OS	Windows	OS Version	10
Product Version	OpenMPT 1.30.10.00 / libopenmpt 0.6.8 (upgrade first)
Target Version	OpenMPT 1.30.11.00 / libopenmpt 0.6.9 (upgrade first)	Fixed in Version	OpenMPT 1.30.11.00 / libopenmpt 0.6.9 (upgrade first)

Summary	0001671: 'Z7F' cutoff commands don't apply properly for OPL instruments unless filter envelope is enabled
Description	For an OPL instrument with no default cutoff and no filter envelope, a `Zxx` cutoff command placed at the starting row of a note doesn't apply until the next note (unless there is another 'Zxx' cutoff command in the meantime, in which case the first never takes effect). This only applies if the note previously had a cutoff value besides `7F`; going from `7F` to another value works normally. This behavior changes depending on whether the instrument has default cutoff or its filter envelope is enabled: if a default cutoff other than `7F` is set, any `Zxx` cutoff command at the starting row of a note has no effect. if the default cutoff is set to `7F`, `Zxx` cutoff commands seem to work as expected (like OpenMPT 1.30.08.00), though `Zxx` cutoff commands of course work differently when default cutoff is set. if the filter envelope is enabled, even if default cutoff is enabled and set to a non-`7F` value, `Zxx` cutoff commands seem to work as expected (like OpenMPT 1.30.08.00).
Steps To Reproduce	An example module is attached that demonstrates the issue. In a new MPTM module, create an instrument and assign an OPL sample to it. In a pattern, enter the example pattern data from this issue's 'Additional Information' section, or other pattern data that resembles it; entering various notes with different `Zxx` cutoff commands at the row they start on will likely demonstrate the bug. Play the pattern; `Zxx` cutoff commands at the start of a note which set the cutoff from a value other than `7F` to something else won't apply immediately. Set a default cutoff value for the instrument and play the pattern. If the value is `7F`, playback should sound normal; if it isn't, the `Zxx` cutoff commands should be ineffective. Disable the instrument's default cutoff, enable its filter envelope and play the pattern. Playback should sound normal.
Additional Information	Examples Instrument `01` is an OPL instrument; it has no default cutoff set and its filter envelope is disabled. `ModPlug Tracker MPT \|A-401...... \|===........ \|A-401...Z00 \|===........ \|A-401...Z7F \|===........ \|A-401...... \|===........` The first two notes sound as expected, but the third note sounds as if it has the cutoff value `0`, like the second note. The fourth note returns to cutoff value `7F`. `ModPlug Tracker MPT \|B-401...... \|===........ \|B-401...Z5F \|===........ \|B-401...... \|===........ \|B-401...Z7F \|===........` The last three notes sound as if they have the cutoff value `5F`. `ModPlug Tracker MPT \|C-501...... \|===........ \|C-501...Z00 \|........Z3F \|........Z5F \|........Z7F \|C-501...... \|===........` All notes sound as expected; `Zxx` cutoff commands seem to work normally when executed anywhere other the starting row of a note. If instrument `01` is changed for instrument `02`, which is an OPL instrument with a default cutoff value of `60` set, the `Zxx` commands in the first two examples have no effect. In the third example, only the `Zxx` commands after the second note's starting row apply. If instrument `01` is changed for instrument `03`, which is an OPL instrument with the filter envelope enabled, the examples sound correct. Example module Instruments `01`, `02`, and `03` match what is described above. Pattern `0` contains the example pattern data above and uses instrument `01`; patterns `1` and `2` are identical to it, but replace the instrument used with `02` and `03`, respectively. Other Cutoff values are reported normally in the 'Patterns' tab status bar. For OPL instruments in OpenMPT 1.30.09.00, `Zxx` cutoff commands don't last longer than the currently active note, and default cutoff isn't applied. Enabling the filter envelope also "fixes" the issue in this version. Cutoff works properly for OPL instruments in OpenMPT 1.30.08.00. r18404 / r18405 may be related but I'm not sure.
Tags	No tags attached.
Attached Files	opl-late-cutoff-sample.zip (790 bytes)

Has the bug occurred in previous versions?	Not as-is; OpenMPT 1.30.09.00 seems to have a related bug
Tested code revision (in case you know it)	18674

Date Modified	Username	Field	Change
2023-02-28 22:01	teimoso	New Issue
2023-02-28 22:01	teimoso	File Added: opl-late-cutoff-sample.zip
2023-02-28 22:12	Saga Musix	Assigned To	=> Saga Musix
2023-02-28 22:12	Saga Musix	Status	new => assigned
2023-02-28 22:12	Saga Musix	Target Version	=> OpenMPT 1.30.11.00 / libopenmpt 0.6.9 (upgrade first)
2023-02-28 22:21	Saga Musix	Summary	'Zxx' cutoff commands don't apply properly for OPL instruments unless filter envelope is enabled => 'Z7F' cutoff commands don't apply properly for OPL instruments unless filter envelope is enabled
2023-03-01 18:49	Saga Musix	Status	assigned => resolved
2023-03-01 18:49	Saga Musix	Resolution	open => fixed
2023-03-01 18:49	Saga Musix	Note Added: 0005574
2023-03-01 18:52	Saga Musix	Fixed in Version	=> OpenMPT 1.30.11.00 / libopenmpt 0.6.9 (upgrade first)

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Saga Musix 2023-03-01 18:49 administrator ~0005574	Fixed in r18782.