Output distortion related to synth gain

Question

Output of FluidSynth seems to distort with some SoundFont files unless gain is set very low, even though output to sound device doesn't appear to be clipping. This problem has been alluded to in the past, by me (Josh Green), but was recently mentioned again on the FluidSynth developers list by Bernat Arlandis i Mañó here:
http://lists.gnu.org/archive/html/fluid-dev/2008-03/msg00002.html

Suspect:

• Reverb and/or chorus
• Volume attenuation and mixing

Reported by: elementgreen

Original Ticket: fluidsynth/tickets/13

该提问来源于开源项目：FluidSynth/fluidsynth

Answer 1

Original comment author: berarma

Hi. I'm Bernat. It's me that reported about distortion for some soundfonts on my system.

Today, I've learned that the problem is caused by the internal mixer of my in-board soundcard. Lowering the master ouput level didn't work, but lowering the PCM channel level did. I've read this is common in cheap audio hardware.

I have an NForce4 chipset, I didn't notice this flaw before. It's strange not all soundfonts were sounding distorted. It seems the amount of distortion is depending greatly on the soundform or something else. It's not simple level saturation.

At first, researching about this related to qsynth/fluidsynth, I read a lot of people is lowering their gain to 10-20 to avoid distortion, and I was doing the same. They might be having this hw problem without knowing it. Having adjusted my alsa mixer to a safe PCM level around 70%, now I can rise the qsynth gain level up to 60-70 without distortion before it starts saturating its output.

I'm using Debian GNU/Linux SID 64bits.

Hope it helps.
Bernat

Original comment by: elementgreen