While 48kbps is significantly lower than the "CD-quality" standard of 320kbps, the use of the -1 high-quality setting helps mitigate the loss of high-frequency detail. It effectively "squeezes" the best possible sound out of a very narrow digital pipe.
This is considered a "low bitrate" setting. It is generally used for speech-heavy content like podcasts, audiobooks, or talk radio where high fidelity is less critical than small file size. For music, 48kbps often results in noticeable compression artifacts (a "metallic" or "underwater" sound). 48kbps mp3(-1 B)
The "B" suffix often refers to CBR (Constant Bitrate) or a specific bit-reservoir management behavior. At 48kbps, using a constant bitrate ensures the file size is perfectly predictable, which is essential for certain legacy hardware or streaming applications. While 48kbps is significantly lower than the "CD-quality"