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Re: [fluid-dev] Floats and doubles, simd and interpolation

From: David Henningsson
Subject: Re: [fluid-dev] Floats and doubles, simd and interpolation
Date: Sat, 27 Nov 2010 15:29:13 +0100
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20101027 Thunderbird/3.1.6

On 2010-11-27 10:35, Pedro Lopez-Cabanillas wrote:
On Saturday 27 November 2010, David Henningsson wrote:
Yesterday, I tried to chase down a bug I discovered - I rendered a song but
a few notes were slightly out of tune, but only when using floats, not when
using doubles!
I wonder what is causing the bug you described though.  If we could
setup a reproducible file rendering case it would probably help track
down the problem.

The soundfont is the standard FluidR3_GM.sf2, the midi file is
, and the first offending notes are on channel 2, ~25 seconds into the
song. The notes are affected by pitch bend, this is probably related
somehow. That's how long I've come so far.

I couldn't reproduce the problem in any of my development machines. Using 
floats or doubles it sounds pretty much alike.

But I've remembered another report about a similar problem, also related to 
notes and pitch bend events:

I couldn't reproduce a wrong behavior playing this song, either.

After long search, I finally found it! \o/

It's committed as http://sourceforge.net/apps/trac/fluidsynth/changeset/395/

Seems like we[1] used fluid_real_t to represent sample offsets at one time, and then the sample offsets got rounded off, so that the loop went slightly longer or shorter.

// David

[1] Looking at svn history, it was my fault originally.

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