Puredata (Pd) is designed for realtime audio processing and control.
As with all digital audio processing systems, a sample rate must be defined in the audio settings menu (the default is typically 44100 or 48000 samples per second).
Audio samples to be sent to the digital-to-analog converter (DAC) or read from the analog-to-digital converter (ADC) of your computer are “bundled” in buffers. The size of these input/output buffers is set via the Buffer size parameter in the audio settings menu.
Larger buffer sizes generally result in more robust (glitch-free) audio performance but produce more input/output audio latency.
Pd audio objects perform “vectorized” computations ... they compute a set number of output samples before sending that data to the next object in the audio network (along an audio patchcord). The number of samples per “vector” is defined by the audio block size, which can be specified using the [block~] object. If not explicitly specified, the default block size is 64 samples.
Most control messages in Pd (such as triggers, bangs and parameter value updates) are processed in between audio block size updates, thus every (sample rate / block size) samples. For a sample rate of 48000 Hz and a block size of 64 samples, this corresponds to a control rate of 750 Hz (or about every 1.3 milliseconds).
Some control rate objects, such as [metro], can run at 1 millisecond increments (faster than the control rate) because they are processed within the audio engine.
