Pure Data opens with DSP off, so no audio is produced until DSP is explicitly turned on

By default Pd opens with DSP (Digital Signal Processing) turned off, so no tilde-suffixed object generates any audio until DSP is enabled. This is deliberate — starting with DSP off prevents accidental loud output on launch — but it is the single most common reason beginners hear nothing. DSP can be turned on in four ways: via the Media menu (DSP On/DSP Off), via the DSP toggle in the Pd window (top-right), via the keyboard shortcut Ctrl+/ to enable and Ctrl+. to disable, or programmatically by sending the message ‘dsp 1’ to ‘pd’ (some helpfiles do this so DSP comes on by itself). The fix for silence is simply to enable DSP.

Examples

After wiring osc~ → *~ 0.2 → dac~, pressing Ctrl+/ turns DSP on and the 440 Hz tone becomes audible; the Media menu shows DSP On / DSP Off.

Assessment

A new Pd user has wired osc~ → *~ 0.2 → dac~ but hears nothing. What is the most likely cause, and what are three ways to fix it?