[Fice]

Scheduling jitter does not cause jitter in audio, because audio is buffered and the buffer is consumed by audio device using it's own clock. Yet OS has to fill the buffer in time or underrun will happen, which will be audible as crackling and stutter. For some applications input and output audio buffers need to be very small to avoid introducing noticeable delay in audio processing, and in this case real-time capabilities are required to prevent buffer overruns and underruns.