{"id":18008,"date":"2025-12-11T20:50:43","date_gmt":"2025-12-12T01:50:43","guid":{"rendered":"https:\/\/scruss.com\/blog\/?p=18008"},"modified":"2025-12-11T20:50:43","modified_gmt":"2025-12-12T01:50:43","slug":"commodore-pet-startup-sound-again","status":"publish","type":"post","link":"https:\/\/scruss.com\/blog\/2025\/12\/11\/commodore-pet-startup-sound-again\/","title":{"rendered":"Commodore PET startup sound (again)"},"content":{"rendered":"\n

I’d posted the commodore pet startup chime<\/a> before without comment, but last weekend’s goings-on at World of Commodore 2025<\/a> have made me revisit it.<\/p>\n\n\n\n

Josh Bensadon had brought some very silly little devices he’d made that played the startup chime when you pressed a button. They contained a small PIC chip programmed with the PWM sequence, a tiny speaker, a battery and the switch. For certain people, it brought so much joy. Retrocomputing folks can be easily amused, it seems.<\/p>\n\n\n\n

I don’t have a PET, but I do have fond memories of the one we borrowed from school during the holidays around 1980. The PET doesn’t have great sound capabilities, as Dave at Tynemouth Software<\/a> notes. But looking at the captured waveform dumped from VICE’s audio output, it looks suspiciously close to four repeats of these 7 steps:<\/p>\n\n\n\n

    \n
  1. 80 cycles of 4329.0 Hz;<\/li>\n\n\n\n
  2. 40 cycles of 2164.5 Hz;<\/li>\n\n\n\n
  3. 20 cycles of 1082.3 Hz;<\/li>\n\n\n\n
  4. 10 cycles of 541.1 Hz;<\/li>\n\n\n\n
  5. 20 cycles of 1082.3 Hz;<\/li>\n\n\n\n
  6. 40 cycles of 2164.5 Hz;<\/li>\n\n\n\n
  7. 80 cycles of 4329.0 Hz.<\/li>\n<\/ol>\n\n\n\n

    Conveniently, all of these steps have the same duration (0.01848 s). The odd series of frequencies seem to be coming from a clock divider: 4329.0 Hz is 1,000,000\u00a0\u00f7\u00a0231, 2164.5 Hz is 1,000,000\u00a0\u00f7\u00a0(2\u00a0\u00d7\u00a0231), and so on.<\/p>\n\n\n\n

    The end result, cobbled together by many calls to sox, sounds like this:<\/p>\n\n\n\n

    Commodore PET Synthesized Startup Chime: mp3<\/figcaption><\/figure>\n\n\n\n

    It sounds not too bad. It doesn’t have the fade-in effect caused by the PET’s power supply coming on, but it has the right character.<\/p>\n\n\n\n

    Its spectrogram is particularly special:<\/p>\n\n\n\n

    \"brightly
    Commodore PET Synthesized Startup Chime: spectrogram. Yes, it’s all square waves<\/figcaption><\/figure>\n\n\n\n

    If you want the sound for a phone notification:<\/p>\n\n\n\n