The SID (Sound Interface Device) is a 3-voice synthesizer chip which gives the Commodore 64 its fascinating sound and lead to thousands of cool SID tunes. If you don't have a C64, you might want to install a SID Player on your PC/Amiga/Mac/whatever.
|1-2||CAP 1A/B||?||Capacitor #1 for the programmable filters. 6581: 470pF, 8580: 22nF*. Note that both capacitors (see pin 3-4) should have the same value.  recommends 2200pF for normal operation, which was AFAIK never used in the C64.|
|3-4||CAP 2A/B||?||Capacitor #2 for the programmable filters. See pin 1-2.|
|5||/RES||in||RESet. If this line remains LOW for at least 10 ø2 cycles, all internal registers reset to zero and the audio output is turned off.|
|6||ø2||in||Phi2**. System clock cycle. All data bus action takes place only when ø2=1.|
|7||R/-W||in||Read/Write. 0=write access, 1=read access.|
|8||/CS||in||Chip select.0=data bus valid, 1=data bus high impedance state (tri-state).|
|9-13||A0-A4||in||Address bits 0-4 for selecting one of the 29 registers.|
|14||GND||-||GrouND (0V). To reduce noise, this line should be connected separately to the power supply.|
|15-22||D0-D7||in / out||Data bits 0-7.|
|23||POT Y||in||POTentiometer Y. Analog input #2 for paddles. (ADC#2)|
|24||POT X||in||POTentiometer X. Analog input #1 for paddles. (ADC#1)|
|25||Vcc||-||Supply voltage. +5V.|
|26||EXTERN IN||in||External Input. Max. input 0.6V.|
|27||AUDIO OUT||out||Audio output of all voices.|
|28||Vdd||-||Secondary voltage. +12V (6581) or +9V (6582, 8580).|
The sound of the two SID versions differs, partly due to different filter capacitors, partly due to the greater number of possible waveform combinations with the new SID. Alas, the filters in the new SID have less effect than the ones in the old SID.
The 8580's digital sound output is quite soft, but you can easily increase the digital volume to make it sound like the old 6581.