<P> Consider an audio DSP example; if a process requires 2.01 seconds to analyze, synthesize, or process 2.00 seconds of sound, it is not real - time . However, if it takes 1.99 seconds, it is or can be made into a real - time DSP process . </P> <P> A common life analog is standing in a line or queue waiting for the checkout in a grocery store . If the line asymptotically grows longer and longer without bound, the checkout process is not real - time . If the length of the line is bounded, customers are being "processed" and output as rapidly, on average, as they are being inputted and that process is real - time . The grocer might go out of business or must at least lose business if they cannot make their checkout process real - time; thus, it is fundamentally important that this process is real - time . </P> <P> A signal processing algorithm that cannot keep up with the flow of input data with output falling farther and farther behind the input is not real - time . But if the delay of the output (relative to the input) is bounded regarding a process that operates over an unlimited time, then that signal processing algorithm is real - time, even if the throughput delay may be very long . </P> <P> Real - time signal processing is necessary, but not sufficient in and of itself, for live signal processing such as what is required in live event support . Live audio digital signal processing requires both real - time operation and a sufficient limit to throughput delay so as to be tolerable to performers using stage monitors or in - ear monitors and not noticeable as lip sync error by the audience also directly watching the performers . Tolerable limits to latency for live, real - time processing is a subject of investigation and debate but is estimated to be between 6 and 20 milliseconds . </P>

Real time system vs non real time system