Archive of UserLand's first discussion group, started October 5, 1998.

Re: MP3 Quality... much better then I thought!

Author:Jeremy Bowers
Posted:7/31/2000; 12:58:19 PM
Topic:MP3 Quality... much better then I thought!
Msg #:19325 (In response to 19321)
Prev/Next:19324 / 19326

I've used "easy cd da" with much success. It's slow though.

Slow is good. More accurately, fast is bad.

Technical overview:

CD drives are incapable of finding the same location twice, unlike a hard drive. When a CD drive seeks on a CD-ROM, it sort of goes to the general location it's looking for, and then takes multiple peeks at the CD contents to see where it is. The CD-ROM filesystem (ISO9660) has a lot of bits dedicated to telling just where on the CD the data is, so the CD-ROM drive aims at "sector 385", and if it peeks at the disk and sees it's at "sector 387", it knows it needs to go back about 2 sectors.

Audio CDs are nowhere near as informative. They have track markers and extremely rare timing data, some of which is only optional. If an audio extracter hits an error, it's impossible to back up to the exact location of the error and try again. Thus, most cheap rippers designed to be out the door ASAP or written by some teenager as a quickie summer project handle this problem by simply glossing over it, leaving in the pops, crackles, and on one of my CD drives at home, buzzes where the audio data is downright wrong. The better rippers back up, grab the data again, and then perform pattern matching to figure out how the two reads match up, and thus how far back the drive head went, allowing the rippers to merge the data and obtain one correct data stream.

The faster the CD reader goes the more likely it is to screw up at some point simply because of speed, until somewhere around 8x where you simply can't rip a song without extreme lossage. On a CD-ROM, the drive can simply go back and try again (and I've often wondered how much time on these 40x drives you can buy is spent doing just that...), but with an audio CD, no such luck. Thus, if you are ripping quickly, odds are you are ripping poorly. (You can get lucky, if you have a top-notch drive and a top-notch CD.) "Fast is bad." I'm getting around 1.3X accurately on a claimed 40x drive.

Thus, the short list of truly good rippers. I think easyCDDA is one of them, as well as cdparanoia (linux/unix), Exact Audio Copy (windows, but a painful program to learn and use), and a very few others, mostly based on those codebases. If you're getting snaps and pops, and the CD is not scratched up (after all, no program can recover from that after a certain point), then you are not using a good ripper, or your drive can't handle audio extraction, even if it "supports" CDDA. (Of the 3 CDROM drives I personally own, 2 "support" CDDA but still can't rip a CD worth a toot, and the other actually got destroyed by cdparanoia, but that's another story that appears to be unique to my system.)

The worst case scenario in ripping is if you are required to listen to the CD as it's being ripped; then the ripper is actually recording audio off of the soundcard input! (At least make sure to shut off all other recording inputs, particularly the microphone.) This adds a mostly unnecessary analog step to the ripping process... "mostly" because it's the only option for some old or broken drives.

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