pd20. Low-pass frequency object in Pure Data

The lop~ object is a low-pass filter.

We had earlier used a noise source (which has a uniform frequency distribution). Now the noise is filtered by a low-pass frequency with a cutoff frequency of 440 Hz.

Thus low-frequencies are passed, without much attenuation below 440 Hz, and with greater attenuation above 440 Hz.

The audio signal shows the effect of filtering:

Because of the low-pass filter, the frequency distribution is no longer uniform but decaying (Analysis menu in Audacity -> Frequency Spectrum):