According to GnuRadio WIki - Throttle:
"A throttle block should be used only if your flowgraph includes no rate limiting block, which is typically hardware (e.g., an SDR, speaker, microphone). It is not intended nor effective at precisely controlling the rate of samples. If you need precise sample rates, the accuracy comes from an actual hardware sink or source, tied to an actual sample clock (USRPs, sound cards,…). GNU Radio itself does not care about "wall clock" time, and sees a signal as a "timeless" sequence of numbers. It operates on chunks of samples, on block, not on a per-sample basis, and not in a fixed rate."
According to GnuRadio WIki - Throttle:
"A throttle block should be used only if your flowgraph includes no rate limiting block, which is typically hardware (e.g., an SDR, speaker, microphone). It is not intended nor effective at precisely controlling the rate of samples. If you need precise sample rates, the accuracy comes from an actual hardware sink or source, tied to an actual sample clock (USRPs, sound cards,…). GNU Radio itself does not care about "wall clock" time, and sees a signal as a "timeless" sequence of numbers. It operates on chunks of samples, on block, not on a per-sample basis, and not in a fixed rate."