The parameters are passed on to LAME. According to the LAME documentation (section “algorithm quality selection”/-q
), the quality value has an effect on noise shaping and the psychoacoustic model used. They recommend a quality of 2 (i.e. -C 128.2
in SoX), saying that 0 and 1 are much slower, but hardly better.
However, the main factor determining the quality remains the bit rate. It is therefore not too surprising that there is no noticeable difference in your case.