以恒定速率循环以高精度进行信号采样 [英] Looping at a constant rate with high precision for signal sampling

问题描述

我正在尝试在 Python 中以 10Khz 的频率对信号进行采样.尝试运行此代码时没有问题(1KHz):

I am trying to sample a signal at 10Khz in Python. There is no problem when try to run this code(at 1KHz):

import sched, time

i = 0
def f(): # sampling function
    s.enter(0.001, 1, f, ())
    global i
    i += 1
    if i == 1000:
        i = 0
        print "one second"

s = sched.scheduler(time.time, time.sleep)

s.enter(0.001, 1, f, ())
s.run()

当我尝试缩短时间时，它开始超过一秒(在我的计算机中，10e-6 时为 1.66 秒).是否可以在 Python 中以特定频率运行采样函数?

When I try to make the time less, it starts to exceed one second(in my computer, 1.66s at 10e-6). It it possible to run a sampling function at a specific frequency in Python?

推荐答案

您没有考虑代码的开销.每次迭代，这个错误都会累加并扭曲时钟".

You didn't account for the code's overhead. Each iteration, this error adds up and skews the "clock".

我建议使用带有 time.sleep() 的循环(参见对 https 的评论)://stackoverflow.com/a/14813874/648265) 并从下一个参考时刻开始计算睡眠时间，这样不可避免的错误就不会加起来:

I'd suggest to use a loop with time.sleep() instead (see comments to https://stackoverflow.com/a/14813874/648265) and count the time to sleep from the next reference moment so the inevitable error doesn't add up:

period=0.001
t=time.time()
while True:
    t+=period
    <...>
    time.sleep(max(0,t-time.time()))     #max is needed in Windows due to
                                         #sleep's behaviour with negative argument

请注意，操作系统调度将不允许您达到超过某个级别的精度，因为其他进程必须不时抢占您的进程.在这种情况下，您需要为多媒体应用程序使用一些操作系统特定的工具，或者制定不需要这种精度水平的解决方案(例如，使用专门的应用程序对信号进行采样并使用其保存的输出).

Note that the OS scheduling will not allow you to reach precisions beyond a certain level since other processes have to preempt yours from time to time. In this case, you'll need to use some OS-specific facilities for multimedia applications or work out a solution that doesn't need this level of accuracy (e.g. sample the signal with a specialized app and work with its saved output).

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