Continuity issue when applying an IIR filter on successive time-frames

Question

I would like to apply a FIR or IIR filter (example: lowpass filter) on successive blocks/time-frames of 1024 samples each.

Possible applications:

Answer 1

As mentioned by @sobek in a comment, it's of course needed to specify the initial conditions to allow continuity. This is done with the zi parameter of lfilter.

The problem is solved by changing the main loop by:

while True:
    b, a = butter(2, 2.0 * f / sr, btype='low')
    if pos == 0:
        zi = lfilter_zi(b, a)
    y[pos:pos+N], zi = lfilter(b, a, x[pos:pos+N], zi=zi)
    pos += N
    f -= 1 
    if pos+N > len(x):
        break

This seems to work even if the filter's cutoff (and thus the a and b) is modified at each iteration.