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#### 7.1.5 SID settings

These settings control the emulation of the SID (MOS6581 or MOS8580) audio chip.

- “Second SID” maps a second SID chip into the address space for stereo sound. This emulates e.g. the “SID Symphony Stereo Cartridge” from Dr. Evil Laboratories. The second SID can be used with software such as “Stereo SID Player” by Mark Dickenson or “The Enhanced Sidplayer” by Craig Chamberlain.
- “Second SID base address” sets the start address for the second SID chip. Software normally uses $DE00 or $DF00, since $DE00-$DEFF and $DF00-$DFFF can be mapped through the cartridge port of the C64. The default start address is $DE00.
- “Emulate filters” causes the built-in programmable filters of the SID chip to be emulated. A lot of C64 music requires them to be emulated properly, but their emulation requires some additional processor power.
- “ChipModel” specifies the model of the SID chip being emulated: there are two slightly different generations of SID chips: MOS6581 ones and MOS8580 ones. Additionally there is "8580D", which refers to MOS8580 with added "Digifix" modification, which adds a DC offset to audio-in, which makes classic samples audible also on the 8580.
- “Use reSID emulation” specifies whether the more accurate (and resource hungry) reSID emulation is turned on or off.
- “reSID sampling method” selects the method for conversion of the SID output signal to a sampling rate appropriate for playback by standard digital sound equipment. Possible settings are:
  - “Fast” simply clocks the SID chip at the output sampling frequency, picking the nearest sample. This yields acceptable sound quality, but sampling noise is noticeable in some cases, especially with SID combined waveforms. The sound emulation is still cycle exact.
  - “Interpolating” clocks the SID chip each cycle, and calculates each sample with linear interpolation. The sampling noise is now strongly attenuated by the SID external filter (as long as “Emulate filters” is selected), and the linear interpolation further improves the sound quality.
  - “Resampling” clocks the SID chip each cycle, and uses the theoretically correct method for sample generation. This delivers CD quality sound, but is extremely CPU intensive, and is thus most useful for non-interactive sound generation. Unless you have a very fast machine, that is.
- “reSID resampling passband” specifies the percentage of the total bandwidth allocated to the resampling filter passband. The work rate of the resampling filter is inversely proportional to the remaining transition band percentage. This implies that e.g. with the transition band starting at ~ 20kHz, it is faster to generate 48kHz than 44.1kHz samples. For CD quality sound generation at 44.1kHz the passband percentage should be set to 90 (i.e. the transition band starting at almost 20kHz).

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