Hi,
Sorry for digging up this old debate, but as a HUGE fan of the ATARI 8 bits computer, I'm gonna add one more quality to the POKEY sound chip

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As said Level42, it has 4 channels, but more important, the 4 channels can do noise ! Where SID has 3 "music" channels and 1 "noise" channel, Pokey has 4 and it makes a great difference ! The same remark applies to the ATARI ST or Amstrad CPC who share the same sound chip (respectively Yamaha YM2149 or General Instrument AY-3-8910, which are the same

) => only one noise channel for them too. So sad.
For music, I agree that SID can do fantastic sounds that Pokey could never do. OK. But for noise, such as engines, explosions, jet engines, etc., Pokey is fantastic because it can combine several noise channels together to make great sound effects.
Just listen the sound effects in Rescue on Fractalus (also known as "Behind Jaggy Lines") : the engine sounds are fantastic !

There can be 4 channels for noise, and the configuration of each of them is pretty rich : such as several settings of the polynomial sequence that is used for the white noise !
Yes, POKEY is great

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