I'm generating an 18kHz sine signal using a dsPIC microcontroller at 44100kHz (I'm not sure I can call it sampling rate, maybe generation rate, although the concept is the same). The dsPIC's DAC then feeds an LM386 amplifier and then an 8-ohm speaker.
Since the generation method is digital, I get harmonics (36kHz) which get aliased, and I hear the parasitic low frequency (8.1kHz) which is something I wish to get rid off.
I was told that I should put an LPF with a sharp cutoff just above 18kHz at the output of the microcontroller so that those high frequency harmonics don't get amplified, but my intuition tells me that I should put an HPF, since by the time the signal is out of the microcontroller it already contains those low frequencies and an LPF will not help.
Am I correct? Thanks!