Hi all,
the panning control (CC 10) currently doesn't really work that well with SoundFonts containing stereo sound (actually with any instrument that has samples with off-center panning).
When an instrument is made up of two samples, one panned hard left (-50) and the other hard right (50) and we issue a note on with the panning CC set to the default 64 (center), the following panning, amp_left and amp_right values are calculated:
Left sample:
pan: -496.062992
amp_left: 0.999969
amp_right: 0.004708
Right sample:
pan: 503.937008
amp_left: 0.000000
amp_right: 1.000000
That's basically what we would expect. The left sample is only audible on the left channel, the right sample only on the right channel.
If we change the panning to hard left (CC 0 10 0) then the following values are calculated:
Left sample:
pan: -1000.000000
amp_left: 1.000000
amp_right: 0.000000
Right sample:
pan: 0.000000
amp_left: 0.706552
amp_right: 0.706552
As you can see, the left sample amp values have remained unchanged (well nearly... rounding problems), but the right sample has moved to center, sounding with equal volume on both channels. When listening to it, it does actually sound a little bit like the position of the sound has moved, but only a little bit. And the overall volume of the sound has increased a little bit. So that's probably not really the intended effect.
Now you could argue that panning on stereo samples is wrong to begin with. We should probably use "balance", not "panning". In other words, simply control the volume of the individual left and right samples, but have each side only output to it's natural channel (right sample only to right channel, left sample only to left channel). MIDI even has a dedicated balance control for that on CC 8. So I guess moving that balance CC to from 64 to 127 (i.e. move the balance to hard right) should gradually decrease the volume of the left sample, leaving the right channel untouched. Moving it from 64 down to 0 (i.e. turn balance to hard left) shoud gradually decrease the volume of the right sample, leaving the left sample untouched. I'm going to prepare a pull-request to add support for balance CC 8.
But my questions to you is: what do we do about the panning control on CC 10 for stereo samples? I see three options:
1. We leave it as is, with the weird and in my opinion wrong behaviour
2. We disable panning completely for samples that are panned to -50 or 50 in the SoundFont
3. We implement the balance logic for all samples that are panned to -50 or 50 (or even for samples with non-zero panning?) in the SoundFont and use the existing panning logic for everything else
I tend to favour option 3, because that is also how most DAWs work: if you use the panning control knob on a mono track, it acts as a mono to stereo panning control. If you use the panning control knob on a stereo track, it acts as a stereo balance control as explained above. We woundn't even need to detect matching stereo samples in the SoundFont. Special casing for samples with -50 or 50 panning values (or even non-zero panning?) should be enough.
What do you think? Is option 3 worth a try?
Cheers,
Marcus