Make oscillator leakage adjustable

[Toddler-Boy]

The current default is 0.01 which is still quite audible, so maybe that should be the maximum.

The minimum would be 0.0 for the cleanest sound.

[Toddler-Boy]

Addendum: It's enough to pass that value in the configuration during initialization, so the DAC class can get that value passed in its constructor.

Also, here's an anecdote: I showed a friend the feature, which was extremely obvious to me, but he couldn't even hear it! He doesn't listen to SID tunes; this is all very weird to him, but even when pointed out, he couldn't hear it. So, I guess this might not need to be adjustable for the casual listener, but for the more hardcore crowd, they will surely notice and might like it "cleaner."

[drfiemost]

Found this paper which gives this formula for the off current:

Ioff = 100 * W/L * 10^(-Vth/S)

where Vth is the threshold voltage, i.e. the Vgs at which Ids=100nA, and S is the subthreshold swing.

So the leakage is inversely proportional to Vth and is theoretically larger for the 8580, assuming similar W/L and subthreshold swing.

[drfiemost]

Recorded /MUSICIANS/C/Cadaver/Metal_Warrior_2.sid outro on both 6581 and 8580.
On the new chip the leakage seems roughly half the amplitude.
Metal_Warrior_exsid.zip

[Toddler-Boy]

In my branch the DAC leakage (for OSC and ENV) can be adjusted. For the filter it’s too expensive and not noticeable enough to justify.

[drfiemost]

Not sure how to handle this, I'm thinking of an optional advanced settings parameter passed to the constructor maybe...

[Toddler-Boy]

Maybe in the config passed to the player? The one struct where you pass the sample-rate, etc.?