Key to Audio-latency test results

  • The red reference line is the global audio buffer size; if this deadline is missed you will hear a sound drop-out.

  • The white line is the actual scheduling latency, the ideal would be the time it takes to play 1 audio fragment (fragment latency).

  • The green line is the time the CPU takes to execute an empty loop (which is calibrated at 80% of the fragment time).

    This is used to simulate heavy CPU computations during the audio play, a typical example could be a synthesizer which computes the waveform to play in realtime.

    Since the thread runs with SCHED_FIFO priority, if this time goes up, then the cause could be the DMA / PCI / ISA contention on the system bus, or busy kernel I/O routines.

  • The yellow reference line is the len of one audio fragment (ideally the white line should stay close to yellow line).

  • The white between +/-1ms is the % of time the total latency stays in the range between +/-1ms of the optimal latency.

  • The white between +/-2ms is the % of time the total latency stays in the range between +/-2ms of the optimal latency.

  • The green between +/-0.2ms is the % of time the CPU loop latency stays in the range between +/-0.2ms of the nominal CPU loop latency.

  • The green between +/-0.1ms is the % of time the CPU loop latency stays in the range between +/-0.1ms of the nominal CPU loop latency.