I/O vector size in Max/MSP sets the tradeoff between audio latency and CPU efficiency

MSP processes audio in blocks called vectors rather than sample-by-sample. The I/O Vector Size determines how many samples are passed between the audio interface and MSP per computational cycle. Smaller vectors give lower latency (faster round-trip from input to output) but higher CPU cost because more vectors must be computed per second. Larger vectors reduce CPU overhead but increase latency — if too large, the CPU may not finish computing in time, causing audio clicks. The Signal Vector Size (internal MSP processing block) affects computational efficiency but not latency. Recommended I/O Vector Size for live performance: no greater than 256 samples.

Examples

Signal vector of 16 samples at 44100 Hz is ~0.36 ms — near-imperceptible for Max messages. Signal vector of 1024 samples is ~23 ms — perceptible delay between trigger and sound. Live performance and MIDI-audio sync require small signal vectors (16-64 samples).

Assessment

A performer hears a noticeable delay between hitting a pad and hearing a response. Which Audio Status parameter should be adjusted and what are the tradeoffs of changing it?