lores~ implements an inexpensive lowpass with an adjustment that lets you add a specified resonance. The middle inlet sets a kind of cutoff frequency, but the sharpness of the filter depends on the resonance passed in through the right inlet (0 is a little bit sharp and 1 as sharp as possible).
There are always ways to reverse engineer objects to do other functions. Here we have inverses the low-res filter to become a high-pass.
The lores~ C source code can be found in the Max SDK examples: http://cycling74.com/downloads/sdk/
Be aware that when using a signal to control the cutoff frequency of lores~, it will not be updated every sample, but only every buffer size. For example, when Max's signal vector size is set to 512, the cutoff frequency will be updated only every 512 samples.
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