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

[Mark Raynsford]

On 2019-02-22T21:29:05 +0000
Mark Raynsford <address@hidden> wrote:
>
> Thanks, this helps a lot. I see what it means now... wGenNdx points to
> the first index (in the same style as PBAG) and I'm actually supposed
> to parse n values starting at that index. The way I was interpreting it
> originally was that there would be n PBAG values and there'd be a 1:1
> mapping between PBAG and PGEN values for a given zone. In other words,
> for each PBAG value, I look up the corresponding PGEN value. With the
> arrangement of PBAG values I showed in basic.sf2, that would obviously
> mean that I'd miss the all-important Instrument PGEN!

I take that back, partially. I'm still not sure about this. Here's the
output from a trivial SF2 that just has a single instrument and doesn't
have any presets (http://ataxia.io7m.com/2019/02/23/trivial.sf2):

TRACE com.io7m.jnoisetype.vanilla.NTParsers: [inst][0] 
NTParsedInstrument{name=NTInstrumentName{value=i0}, instrumentZoneIndex=0}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [ibag][0] 
NTParsedInstrumentZone{generatorIndex=0, modulatorIndex=0}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [ibag][1] 
NTParsedInstrumentZone{generatorIndex=0, modulatorIndex=0}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [igen][0] 
NTParsedInstrumentZoneGenerator{generatorOperator=17, 
amount=NTParsedGenericAmount{value=0}}
TRACE com.io7m.jnoisetype.vanilla.NTParsers: [igen][1] 
NTParsedInstrumentZoneGenerator{generatorOperator=53, 
amount=NTParsedGenericAmount{value=0}}

So I start at INST[0]. The spec says:

"The first zone in a given instrument is located at that instrument’s
wInstBagNdx. The number of zones in the instrument is determined by the
difference between the next instrument’s wInstBagNdx and the current
wInstBagNdx."

Well, there isn't a next instrument, so I make the obvious assumption
that all of the zones given in IBAG belong to the one defined
instrument. So, I first inspect IBAG[0] and see that the generator
index field points to IGEN[0]. The spec says, for modulators (it seems
to miss this information in IGEN as it does the corresponding paragraph
in PGEN that you noted was missing):

"The zone’s wInstModNdx points to the first modulator for that zone,
and the number of modulators present for a zone is determined by the
difference between the next higher zone’s wInstModNdx and the current
zone’s wModNdx. A difference of zero indicates there are no modulators
in this zone."

So in other words, in order to know how many elements of IGEN I need to
inspect for the IBAG[0] zone, I need to look in IBAG[1]. Well, the
generator index value in IBAG[1] is 0. So... What does that mean? The
spec says, for modulators, that a difference of zero indicates that
there are no modulators for the zone. Clearly there are generators for
the zone. How do I know how many to consume?

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

pgpP_s5x5IrIf.pgp
Description: OpenPGP digital signature