Mp3 bitrate and frequency question

I listen to lots of audiobooks and have recently started sharing with friends. I find myself rather confused by the whole bitrate/frequency question.

The recommended settings (in the spoken word/audiobook scene) as a compromise between quality and file size are 64 kbit/s, 44 khz, mono.

However, I have a whole lot of files which I created ages ago before I knew any of this. They were ripped with Nero (which I no longer use) and used the Nero Mp3 Pro settings, which result in files which are 80 kbit/s and 22 khz, stereo.

As a total ignoramus, I’m trying to get my head around comparing 64 kbit/s 44 khz with 80 kbit/s, 22 khz.

The practical question is whether it is worth the bother of re-ripping the CDs to 64 kbit/s 44 khz, or whether I should keep the 80kbs, 22khz files and just use dbPoweramp to convert them from stereo to mono, to reduce the file size.

I suppose the underlying question is which is more critical - the bit rate or the frequency and whether the higher bit rate (80 as compared to 64) makes up for the lower frequency (22 as compared to 44)?

The second question is, if I use a program like dbPoweramp to convert the 80 kbit/s, 22 khz files to mono, leaving all the other settings the same, am I going to lose much in the conversion process (ie, I belive that every time you process a file, you lose something in the process)?

Converting them would only result in a 20% space savings (64/80=.8 or 80% the size). Sampling frequency and Mono or Stereo don’t enter into file size, it’s strictly bitrate times time. You won’t gain anything quality wise and in fact will probably end up with a few different kinds of additional distortions in re-encoding them, so unless you really need the space, I’d leave them alone. As far as Sampling rate goes, there’s this thing called the Nyquist factor which basically states that you need to sample at at least twice the highest frequency of interest. Voice generally rolls off at about 8KHz, so 22 KHz sampling is more than adequate. Music goes to about 20 KHz so 44 KHz is an appropriate sample rate for that.

Thanks for the info. It’s a big help. However, I’m a bit confused about the stereo/mono thing, as on the newsgroup FAQ site, they emphasize that stereo files are bigger than mono files, because they include information for 2 separate tracks. Are they just ignorant and deluded?

Bitrate is Bitrate, period. A stereo file uses either half the allocated bitrate for each of the two channels (normal stereo) or, in ‘Joint’ stereo most of the bitrate for the sound that is common to the two channels and less for the ‘difference’.

Are they just ignorant and deluded?


Thanks for the replies - it’s amazing how much one has to learn… This forum really stands out as far as being helpful to newbies is concerned. I have been to others where the standard practice is to ridicule people who don’t know what the cognoscenti think is “obvious”.