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TOPIC: Understanding Attenuation

Understanding Attenuation 3 years 5 months ago #1

  • Dan Eble
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I've created presets in Polyphone using a sine wave sample with 72 dB, 48 dB, and 0 dB attenuation, then rendered a 1-s tone of each with Fluidsynth, then put the wav files through Audacity's spectrum analyzer.

The difference in the peaks is only about half as much as the numbers provided to Polyphone, and I don't understand why. Is this a suitable way to verify the effect of the attenuation parameter? Thanks.

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Understanding Attenuation 3 years 5 months ago #2

  • Davy
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Hello,

Could you please do the same test with fluidsynth?

At the beginning of Polyphone I tested the sound engine against fluidsynth and I was surprised the same way. I don't remember exactly how I did but the factor 0.5 was added to reproduce the fluidsynth behaviour. An error is not excluded.

Regards,
Davy
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Understanding Attenuation 3 years 5 months ago #3

  • Dan Eble
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Davy wrote:
Could you please do the same test with fluidsynth?

Thanks for the reply. I'm not sure what you mean. The test I performed used Fluidsynth. The role of Polyphone in the test was merely SoundFont editor.

I thought of one possible variable affecting attenutation: the note velocity in my MIDI files was the editor's (Aria Maestosa) default of 80. I changed it to 127 and got results similar to the first test.
Last Edit: 3 years 5 months ago by Dan Eble.
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Understanding Attenuation 3 years 5 months ago #4

  • Davy
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Ok I read your message too quickly.

For sure, the attenuations set in Polyphone are correct (I already tried to save with Polyphone and open with Swami for instance). But as I said, when I listened to the result between Polyphone and Fluidsynth I also remarked the additional factor 0.5 for the attenuation. I have no answers where it comes from but for consistency I also added it in the sound engine of Polyphone. Maybe you should ask the fluidsynth team directly.

The final attenuation depends also on the velocity, that's why you need to test with 127 (full velocity). A lower velocity may also alter the sound with a low pass filter.

Davy
Last Edit: 3 years 5 months ago by Davy.
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Understanding Attenuation 3 years 4 months ago #5

  • S. Christian Collins
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Preset/Instrument level attenuation should attenuate 0.4 dB for every 1 dB that you specify (and this is what FluidSynth does). The reason for doing this is compatibility... this is how Creative/E-MU designed their synth engines (I have personally measured dB levels to verify this), and the thousands of SoundFonts out there expect this behavior.
Last Edit: 3 years 4 months ago by S. Christian Collins.
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Understanding Attenuation 3 years 4 months ago #6

  • Davy
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Hey thanks for the information!
I will change the multiplier, for compatibility ;-).
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