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Hi,

I’ve been comparing fmod to our old sound system the last few days. Everything sounds pretty good, but today my sound designer noticed a problem with a couple sounds. I tracked down the sounds that sounded different, and found that they were all having their frequency modulated in different ways.

For sound that we drop the frequency (lower pitch), everything sounds fine. At least, it’s hard to tell a difference. However, for some sounds where we increase the frequency (higher pitch), there is a noticeable difference between fmod and directsound.

Unfortunately, it sounds a lot worse in fmod.

I was wondering if anyone here has noticed this difference at all? I’m not sure how the directsound and fmod algorithms differ, but if anyone has any insight I would appreciate the help.

thanks,
sam

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Are you comparing apples to apples? i.e. both systems using hardware or software? Are you comparing 3d sounds or simply 2d sounds that have their frequency set? Can you record the output of both methods and send us a wav that shows the difference? If your old system uses hardware 3d then the difference you’re hearing might be EAX filtering?

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Hi Andrew,

I am comparing apples to apples.. At least I hope I am. I’m going to double check. The sounds are both 1-channel sounds playing in software as 2d sounds. The source is 44khz 16-bit raw samples.

I’m working on recording the output of both. Will send them your way soon.

-sam

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There is no issue here, you are comparing linear interpolation vs a higher order interpolation which is what directsound uses.

FMOD’s mixing is far faster than directsound by using this technique, but we support 4 different types of software based interpolation so if you choose one of the more expensive ones, it will sound the same.

[code:mry5bzfj]
FMOD_DSP_RESAMPLER_NOINTERP, /* No interpolation. High frequency aliasing hiss will be audible depending on the sample rate of the sound. /
FMOD_DSP_RESAMPLER_LINEAR, /
Linear interpolation (default method). Fast and good quality, causes very slight lowpass effect on low frequency sounds. /
FMOD_DSP_RESAMPLER_CUBIC, /
Cubic interoplation. Slower than linear interpolation but better quality. /
FMOD_DSP_RESAMPLER_SPLINE, /
5 point spline interoplation. Slowest resampling method but best quality. */
[/code:mry5bzfj]

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Excellent, this is exactly what I was looking for!

thanks,
sam

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