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30 lines
1.6 KiB
Text
30 lines
1.6 KiB
Text
Investigating how Doom decides on a voice to discard when it runs out
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of OPL voices.
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Findings so far:
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* The instrument affects the voice that is released (different instruments
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give different results). It is the instrument data that is significant,
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not the instrument number (identical instruments behave the same - 87/88)
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* Sometimes notes are not turned off when they should be. Sometimes notes
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are turned off when they should not be (bug?)
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* DMX maintains a linked list of the most recently-allocated voices. These
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are searched backwards when finding a voice to free, so the most recently
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allocated voices are the first to be freed.
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* Different MIDI channels have different "priorities", somehow affected
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by the instrument in use on that channel.
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* When no voices are available, the will search back through the allocated
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voices list and discard the most recently used voice from a channel of
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a lower priority to the channel for the new note.
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* If no lower-priority voices are available, a voice from the same
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channel will be discarded.
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* If no voices from lower priority channels are available, and none from
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the same channel, the first voice in the list is discarded, ignoring
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priority.
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* Priority seems to be determined by MIDI instrument number - lower
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instruments have a higher priority than higher instruments, so instrument
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0 defeats 1, 1 defeats 2, etc.
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* If a double voice instrument is played, and there are no free voices,
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a voice will be sacrificed to play the first voice of the instrument,
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but the second voice will not be played.
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