Editing Atari 520ST (section)

== Sound Capabilities ==
* PSG: Yamaha YM2149F (AY‑3‑8910 derivative) – 3 independent square‑wave tone channels plus 1 noise source; 5‑bit amplitude registers with 5‑bit envelope generator and 8 preset shapes; 8 octave range. No analog filter.<ref>{{cite web|url=https://temlib.org/AtariForumWiki/index.php/Yamaha_YM2149_Manual|title=YM2149 manual (features)|publisher=AtariForumWiki|access-date=2025-08-13}}</ref>
* Digital audio: No dedicated PCM in 520ST; CPU‑driven sample playback possible by rapid volume register updates or timer‑driven DAC on parallel port in software (common in demos and some games).<ref>{{cite web|url=https://www.goto10retro.com/p/sounds-of-the-atari-st|title=Sounds of the Atari ST (historical overview)|author=Paul Lefebvre|publisher=GoTo10Retro|date=2024-01-10|access-date=2025-08-13}}</ref>
* Audio I/O: Mono line‑level out and an audio‑in on the 13‑pin monitor port (approx. 1 Vpp nominal).<ref>{{cite web|url=https://www.oldcomputers.it/parts/atari/1040STF/docs/connettore_monitor_st.htm|title=Monitor connector – audio in/out levels|publisher=oldcomputers.it|access-date=2025-08-13}}</ref>