[fluid-dev] Slightly OT: Parsing SF2; duplicate pbag entries?

[Mark Raynsford]

Hello.

Apologies for the slightly off-topic question, but I can't think of a
better group to consult when it comes to SoundFont questions.

I'm currently working on some Java code to parse SoundFonts. While I've
completed the actual parsing in the sense that I can extract all of the
data from a given SF2 file, I'm struggling to interpret some of that
data. Specifically, I'm seeing pbag entries in valid and playable
SoundFonts that don't make any sense to me, and I can't seem to find
an explanation for them in the spec.

Here's an example of parsing one such soundfont
(http://ataxia.io7m.com/2019/02/22/basic.sf2):

TRACE com.io7m.jnoisetype.vanilla.NTParsers: [phdr][0] 
NTParsedPreset{name=NTPresetName{value=p0}, preset=0, bank=0, presetBagIndex=0, 
library=0, genre=0, morphology=0}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [phdr][1] 
NTParsedPreset{name=NTPresetName{value=p1}, preset=1, bank=0, presetBagIndex=2, 
library=2, genre=2, morphology=2}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [pbag][0] 
NTParsedPresetZone{generatorIndex=0, modulatorIndex=0}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [pbag][1] 
NTParsedPresetZone{generatorIndex=0, modulatorIndex=0}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [pbag][2] 
NTParsedPresetZone{generatorIndex=2, modulatorIndex=0}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [pbag][3] 
NTParsedPresetZone{generatorIndex=2, modulatorIndex=0}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [pgen][0] 
NTParsedPresetZoneGenerator{generatorOperator=43, 
amount=NTGenericAmount{value=32512}}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [pgen][1] 
NTParsedPresetZoneGenerator{generatorOperator=41, 
amount=NTGenericAmount{value=2}}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [pgen][2] 
NTParsedPresetZoneGenerator{generatorOperator=43, 
amount=NTGenericAmount{value=32512}}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [pgen][3] 
NTParsedPresetZoneGenerator{generatorOperator=41, 
amount=NTGenericAmount{value=1}}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [inst][0] 
NTParsedInstrument{name=NTInstrumentName{value=i0}, instrumentIndex=0}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [inst][1] 
NTParsedInstrument{name=NTInstrumentName{value=i1}, instrumentIndex=3}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [inst][2] 
NTParsedInstrument{name=NTInstrumentName{value=i2}, instrumentIndex=6}

Note that file contains two presets, p0 and p1, and those presets link
to the i0 and i2 instruments via the pgen[1] and pgen[3] entries.
However, according to the spec, I have to read pbag entries starting at
the presetBagIndex for each preset. So, when I read pbag[0] and pbag[1]
as part of interpreting p0, I encounter:

TRACE com.io7m.jnoisetype.vanilla.NTParsers: [pbag][0] 
NTParsedPresetZone{generatorIndex=0, modulatorIndex=0}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [pbag][1] 
NTParsedPresetZone{generatorIndex=0, modulatorIndex=0}

Duplicate entries that both point to pgen[0]. Not pgen[0] and pgen[1]
as I would expect.

I've inspected the data in a hex editor and those duplicate entries are
definitely present. Multiple SF2 implementations (including Fluidsynth)
parse and play them correctly.

How do I interpret those presets such that I can correctly link them to
the instrument definitions?

-- 
Mark Raynsford | http://www.io7m.com

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