The TIA chip is responsible for both the audio and visual graphics of the Atari 2600. On the audio side, it has 2 oscillators with 16 different types of "waveform" each. Each oscillator has 5 bit pitch depth with 32 separate values. This results in some very out of tune tonal pitches. Also, each "waveform" is tuned differently, relative to the tuning values.
Links:
Sound programming guide via Paul Slocum here.
