The website for the SIDney says that "The emulator provides some control over the 'analogue' section. The S/N ratio
can be configured from inaudible (just used to prevent denormal of the filter)
up to irritating levels. Oscillator leakage is configurable from none up to
Do I have to edit this at code level or is it not implemented yet?
Ah, no, this is not a visible parameter. The softSID provides a parameter that is the S/N ratio, it is basically leakage into the filter. The filter is always given an amount of noise which should be below an audible threshold to prevent it going to 100% with zero input - denormal. This noise injection level is configurable but only with a compiler.
The default value is empirical which just means I configured a level that for me was 'just' audible. The next version of a bristol softSID synth will give access to this.
To be complete, there are the following parameters that the chip accepts but that the GUI does no provide access:
S/N ratio: filter noise level
Leakage: oscillator leakage level into the filters.
DC Bias: nominal DC signal level
Volume: output signal gain
Clock rate: the rate of the nominal clock (this was a bug fix for your tuning issue).
Detune: applies adjustments to waveforms in Multi mode.
So in short, to answer your question, yes, most of this stuff is only configurable at the code level.