Filtering a Morse code (CW, OOK) signal
The bandwidth of the message content of a CW signal in Hz is roughly at least 4 times the WPM at which the dots and dashes of each Morse Code character are being keyed.  The actual signal may take up a several multiples of that bandwidth, depending on the envelope shaping or the rise/fall time of the CW transmitter used to prevent key clicks. (Plus a few harmonics of a Morse Code dot's AM modulation envelope may be required for a typical radio operator to reliably copy dots by ear, requiring a bandwidth multiple corresponding to that harmonic number).  So any audio filter bandwidth needs to be at least that wide to pass a Morse Code signal, either by measuring the WPM of the signal, or using some maximum WPM expected.