View Issue Details

Jump to NotesJump to History
IDProjectCategoryView StatusDate SubmittedLast Update
0001722OpenMPTPlayback Compatibilitypublic2023-07-25 06:372023-07-25 07:26
Reportersqrmax Assigned To 
PrioritynormalSeveritymajorReproducibilityalways
Status closedResolutionno change required 
Platformx86 / x64OSWineOS VersionXP, macOS/wine
Product VersionOpenMPT 1.31.03.00 / libopenmpt 0.7.2 (upgrade first) 
Summary0001722: Stereo separation --- lower than 100% mutes channels and samples
Description

In some modules, selecting stereo separation less than 100% leads to strange sound. Consider for example Penetrating Light by Necros (attached). If you set the stereo separation to 25%, channels 4 and 5 sound muted, and for pattern 50 you get some really strange sample volume behavior compared to 100% stereo separation. I thought stereo separation related to how the channels differ from each other in terms of panning and such, and that zero stereo separation equals mono. Is the observed behavior really as intended?

Steps To Reproduce

  1. Open MPT, load attached light.s3m module.

  2. In the mixer settings, set stereo separation to 100% and play the song.

  3. In the mixer settings, now set stereo separation to 25% and play the song again. In many patterns, channels 4 and 5 sound muted, and later on pattern 50 specifically sounds quite different in terms of the volume for each channel / sample.

Additional Information

I first noticed this behavior in the "converted" modules from Necros' musicdisk Digital Psychosis (which has DSM modules, for which S3M and MOD "converted" versions exist). An additional note: I actually recorded the original musicdisk playing on DOSBox to make sure the audio channels do not sound like what you get with 25% stereo separation --- and found that although DOSBox recorded the audio in 16 bits stereo, the sound data was mono.

The same behavior occurred in 1.28.09 running on XP (which is where I saw it first).

TagsNo tags attached.
Has the bug occurred in previous versions?Yes
Tested code revision (in case you know it)1.28.09, latest

Activities

sqrmax

sqrmax

2023-07-25 06:40

reporter   ~0005759

The website apparently refused to accept an uncompressed s3m file.

light.zip (202,753 bytes)
Saga Musix

Saga Musix

2023-07-25 07:26

administrator   ~0005760

Those channels use Pro-Logic Surround (command XA4), which works by inverting the phase of one of the right channel. This creates this a spacious sound despite the source being a mono signal. When lowering the stereo separation, the left and right channel move closer together, eventually turning into a mono signal. However, Adding a signal to a phase-inverted copy of the same signal results in a silent signal, hence reducing the stereo separation more and more makes the signal quieter and quieter.

If you want just the normally panned channels to be closer together but not touch the surround channels, stereo separation cannot help you. You will have to edit the channel pan commands instead.

Issue History

Date Modified Username Field Change
2023-07-25 06:37 sqrmax New Issue
2023-07-25 06:39 sqrmax OS Version (version plz) => XP, macOS/wine
2023-07-25 06:40 sqrmax Note Added: 0005759
2023-07-25 06:40 sqrmax File Added: light.zip
2023-07-25 07:26 Saga Musix Note Added: 0005760
2023-07-25 07:26 Saga Musix Status new => closed
2023-07-25 07:26 Saga Musix Resolution open => no change required