[Linuxsampler-devel] Re: Gigasampler curve types

[Mark K. <mar...@co...>]

On Sun, 2003-11-02 at 08:41, Christian Schoenebeck wrote: 
> Es geschah am Sonntag, 2. November 2003 15:20 als Mark Knecht schrieb:
> > On Sun, 2003-11-02 at 02:15, Christian Schoenebeck wrote:
> > > Perfect would be a simple list with
> > >
> > > 	velocity value		-		output level (dB)
> > > 	...
> >
> > How can I get you this list and make life perfect? I'd like to learn to
> 
> Unfortunately I don't know of an app that does that automatically, so you 
> should use your Protools sample editor and read the peak value of each 
> triggered sample and write that by hand simply into a text file (sorry, 
> boring work - i know). If your editor allows multiple scales for displaying 
> amplitude then better do not choose dB. Else we would have to recalculate 
> that to an non-exp. value anyway, so best would be the direct "raw" value of 
> the sample point (e.g 39458).

Hi,
   First off, while we want to operate like GSt, in my mind at least we
don't need to be exactly identical. We should do what's right, I think,
and then wait for some feedback from early users as to how it sounds. I
think you'll find from my data below that GSt, while a good program, has
some really strange operation when you dig in as deeply as I did today.

   My first results are sort of strange, and I'm learning a lot as I go
along. I hope this ends up making sense. I've downloaded and run
Trachtman's MIDI file against his special gig file. Some of those
results look pretty good, but none of them look identical to what's on
his web site. The MIDI file is good, so I'm using it with a new gig file
I built using a 5KHz sine wave on one note. This seems to be working,
but it has produced some results I'm not totally comfortable with.

   Also there are a large number of possibilities just in this small
part of GSt's editor. We have the Velocity Response, 3 values, Dynamic
Range, 5 values, and Curve scaling, 128 values, giving us a 1920
possibilities. Not fun. We need to constrain this to a reasonable amount
of work.

   OK, so using the default settings (non-linear, high & 20) AND the
default GSt mixer settings (-6db on the channel volume, and -6 db on the
mixer volume) I actually get VERY strange audio into Pro Tools. Of the
128 pulses I record, there appear to be only 13 distinct volumes. They
go in groups that are sort of evenly spaced, so you get sometime 7-10
pulses with the same volume, and sometimes only about 4 with the same
volume. Also, with these mixer settings, the linear and non-linear are
not that different. Weird, 'eh? I think this may be a bug.

   Another 'bug' I notice, or maybe a limitation of the GSt coding, is
that the first 2-4mS of a new pulse has the volume of the pulse
preceding it, and then the right volume. I want to look at this more
later. I'm wondering if this could be some psycho-acoustic thing they're
doing? (More likely just a mistake...)

   OK, so not liking ANY of that data, I then changed the default volume
settings and pushed them both up to maximum volume. This gives results
that are much more reasonable. Here's what I see:

NL-high-20 - The first 15 pulses (MIDI velocity 127-113) are at maximum
volume. After that there are sort of 2 long straight lines for the rate
that audio decreases at, so that it sort of looks like a slow decay. The
first group is 21 pulses long (MV 112-92) and gets down to about 45%,
then a group of about 28 pulses (MV 91-64) where it goes down to about
15%. After that there is a group that goes out to MV 24 and gets down to
about 5%. After that it just stays at 5% from MV 24 to MV 0.

L-high-20 - The first 21 pulses (MV 127-107) are at maximum volume.
After that it's a linear drop to 2% volume at MV 0.

S-high-20 - This is an accelerated exponential drop off. The first 17
pulses are at maximum volume. After that it falls of pretty quickly
(very exponential in looks) so that 12 pulses later you're down to
around 20%, and then there are sort of 4 equally sized groups of pulses
down to about 2% volume at MV 0.

   Strange results, yes?

   OK, so more work to do. I then looked at Curve Scaling == 0. This
doesn't have much effect on anything with Dynamic Range is set to high.
I get curves that are pretty identical to the curves described above. So
next I pushed Dynamic Range to low and recorded more data. This was very
interesting.

NL-low-0 - 40 pulses (MV 127-88) at maximum volume, then  a straight
line of 10 samples (MV 87-78) down to about 80% volume, then a straight
line all the rest of the way to MV = 0 where the volume is about 25%

L-low-0 - Very interesting results! 128 pulses at maximum volume.

S-low-0 - Almost a copy of NL-high-20 up above.

   So, I hope from all of this data you should have enough to get
started. I don't have the patience (really, I don't!) to try and sit in
Pro Tools and make tables of exact values, but I'm not sure it's that
necessary. As soon as you get something in LS, I'll build it, record
audio using it, and do a visual comparison of these settings and more.
Maybe if someone on the list knows how I could take these wave files and
extract the exact values automatically, using sox or some other tools,
then I'd be happy to try that if it's not going to consume huge amounts
of time. Please remember that each wave file is stereo and contains 128
audio pulses.

   I hope you think this is reasonable. Just getting this data took
about 3 hours. 3:15 in the afternoon. No music done yet. I'm gonna write
a song today if it kills me! ;-)

   Let me know if you or anyone else needs additional clarification.

Cheers,
Mark