Can highpass and lowpass filtering music before MP3 encoding improve perceived audio quality?

Distribution of music files often include performing MP3 encoding, especially when utilizing streaming services. Lossy encoding is susceptible to create audible artifacts in the encoded audio material, especially in the high frequency area. To explore highpass and lowpass filtering music as potential adaptation methods to the end media, a listening test was projected where nineteen subjects were exposed to four different adapted MP3 files and one reference MP3 file, at two different bitrates, and were instructed to grade the audio quality of each. Multiple t-testing showed little difference regarding bitrates, why continued analyses were performed on the combined material. Generally, it was found that the reference stimuli scored the highest why it is concluded that highpass and lowpass filtering had a subjectively negative effect on the audio material and that non-filtered MP3 files are favorable to filtered MP3 files. The filtering was found to have some effect in the overall frequency spectrum, however inconclusive