I'm trying to convert old cassette tapes to MP3 using a USB device through Audacity. I know very little about audio so I'm not interested in getting into all of the technical stuff but just wondering what the use is for difference Hz when recording. Will a higher speed improve the quality or is it best to leave it alone considering I'm a newbie. I've currently been recording everything at the default 44100.
It's really up to you. If you want to make a CD from it, 44.1 khz or 88.2khz is ideal since it will avoid resampling errors when going to CD's 44.1khz audio. If you want to use it for video or just for your own files that you listen to digitally, then I'd probably go 48khz or 96khz.
The advantage of using 88.2 or 96 is that it reduces certain types of errors that can occur when making adjustments to the audio prior to producing your final output. If, for example, you plan to try to reduce the tape hiss, then it may be advantageous to use the higher initial sample rate so you can reduce it without rounding errors later.
Format of MP3 already includes data compression so it'd be better to use 48000, 24 bit in order to maintain some level of sound quality into MP3 format later.