Simple first order low pass filter as described here: https://en.wikipedia.org/wiki/Low-pass_filter#Simple_infinite_impulse_response_filter
It applies a low pass filter on a vector of samples. It mutates the input array. Therefore, the number of output values equals the number of input values.
Applies a low pass filter on a vector of mono sample in 16 bit resolution. If you have stereo data, call this function for each channel, convert it first to mono or do whatever fits your use case.