Elecraft recently announced that they are adding an Audio Peaking Filter (APF) to the K3 transceiver. The DSP APF filter is modeled to perform like analog APF filters such as the praised one found in early Yaesu FT-1000D transceivers. The filter is easiest described as the opposite of a notch filer as it applies gain to a very narrow passband and attenuates anything outside this passband. This is especially useful when trying to pull extremely weak signals out from the noise.
During the weekend I tried an early beta version of the firmware with the APF filter and it worked very well for enhancing readability of weak signals. In some cases it really made a difference allowing me to copy signals otherwise not readable. In my opinion the filter works very well, listen to the A/B tests below to form your own opinion. The two recordings of BU2AQ where made on Topband using a pennant RX antenna pointing North East. Both recordings starts with APF engaged, then after a few seconds the filter is toggled off/on.
Unfortunately the beta firmware posted before the weekend was very buggy and it has been withdrawn for now, but I expect Elecraft to post new updates within a few days.
73 de Björn, SMØMDG