I saw the following explanation on the web.
Who can i set the "input sensitivity" on the luna recordin mixer?
Thanks!
If you are using only a single sound from a multitimbral synth, try to increase the output level of this single sound internally to minimise the noise contribution of the synth's output electronics. For the same reason, always leave your synths' physical output level controls at maximum. Once you've done these things you can just choose the soundcard input sensitivity that lets the synth's peak recording levels get closest to 0dBFS without actually clipping.