do you have one of those cheap mp3 players? you know the kind.. they have around 1 to 4gigs of flash.. cost about 10$ at most... use either a single AAA cell or have a tiny lithium-ion that gets around 5hrs of play time.. and you mostly use it in your car... or at the gym...
this will be much more handy to those with the 1gig units than the 4 but every little byte counts...
mp3 has severe aliasing problems with any frequency above around 16khz .. the same cutoff point that the FM radio broadcasts to you... so in encoding it very much 'muffles' those sounds and completely does away with the highest frequencies... with a high-end hi-fi you'll notice.. in a car? not so much... after all the radio stations are getting away with this trick
ok so whats the point? to save data and cram more music on that cheap little player in a way that sounds not half bad...
specifically we feed this to the 'lame' mp3 encoder; lame -h -V 5 --resample 32000 --lowpass -1 input.wav output.mp3
what? ok heres the breakdown.... '-h' is for high quality... you should add this to any encoding.... '-V 5' is the variable bitrate range of around 96 to 112kbit we can get away with since we are cutting the frequencies above 16khz with '--resample 32000' and since we are cutting those frequencies the lowpass filter can be disabled with '--lowpass -1'
the lowpass filter being disabled gives better quality highs on a 32khz file compared to the 44khz file where disabling the filter presents aliasing effects even into 320kbps ... variable bitrate saves data overall allowing more music to be crammed into the player... in my own experimenting i saved around 900kb to 1mb per 4mins of music encoded... and this does add up... given the bonus that the music sounds better its win win overall...
why did i write this? well.. i was really bored... and tinkering with the lame encoder trying to rid it of both filtering and aliasing... this was the only way i found to do that and stay in the mp3 iso spec.. just so happens it saves quite a bit of disk space in the process.. so those really old 'thumb drive' mp3 players still have a use...
oh... and as for a 44khz file
without aliasing... well... that would be;
lame -h --freeformat -b 640 -m d --lowpass -1 input.wav output.mp3
sounds perfect... but takes up about half the space of the flac file i encoded it from and doesnt work in all decoders... actually doesnt work in most decoders... and yes, thats 320kbit per channel... same as a mono 320kbit... ..its just wasteful and something mp3 cant really do... ..tho if you try this and find that your mp3-only portable player can actually decode it then.. well.. enjoy
