I've noticed if I downsample my classical guitar recordings from 44100Hz to 8000Hz, the result is a bassy vintage electric guitar sound, which I really like in some songs of mine.
I know because of the sampling theorem, the downsampling involves cutting all frequencies above 8000/2=4000Hz. I did the same on the original 44100Hz signal, applying a low pass filter at 4000Hz with 48db steepness (maximum allowed by the Audacity software I am using), but could not recreate the same downsampled tone with just this.
I used Audacity Spectral Selection and then the spectral delete plugin to delete all frequencies above 4kHz, just like downsampling at 8kHz does but without loosing quality. This is a great way to simulate a guitar pickup if you record your classical guitar with a good external condenser mic like I do.
Do you know what else is going on downsampling? Or how can I find out out? I would like to have the same altered tone I get with downsampling, but without loosing sound quality, keeping the signal sampled at cd quality.