First, let's be clear: this is about saving audio files you have worked on. Where and how you archive a copy of that CD you bought on eBay is a whole other subject. This is about that surreptitious concert tape you spent half a day rebalancing and de-hissing; the rare LP you spent hours de-clicking and selectively compressing. Now you have a batch of WAV files and an audio CD, maybe a spare CD just in case. That's not necessarily good enough, though; what are the options for making a copy that will last and will give you the same quality CD-DA next year that you burned today?
It may come as a shock, but CDs (and DVDs) do not have unlimited life. A well made pressed disc or a well written recordable one should last for decades, but various ills can beset either and failure can occur in as little as a year. If the material is of value, it is worth handling with care and backing up in an archive.
Music (CD-DA, Compact Disc - Digital Audio) and data are recorded differently. By saving one layer of error correction, CD-DA has about 13% more space for audio than would be available on a data disc of WAV files. But that 13% is valuable in an archive to provide more tolerance for errors accumulating over time. To take advantage of the error correction, one would need more than a single data disc to hold the WAVs corresponding to a music disc. The logical solution is to compress the WAVs to another format so they fit. The most popular such compression, MP3, is "lossy" - it approximates the sound more or less well, but never allows full recovery of what was in the WAVs. It is possible to compress a WAV file so that there is no loss just as ZIP or RAR can compress a data file without compromising its content. Some years ago, I discovered that with one compressor, APE from http://www.monkeysaudio.com/ I proved that it was lossless by compressing a WAV file, then decompressing the resulting APE file and checking that the resulting WAV was identical to the original. I could switch to another, but I'm happy with APE for its interface and its performance; it works, so I won't fix it.
Hey, you've got that spare audio (CD-DA) disc; you can just run a copy from that. Right?
You can, but that may not be your best choice. The potential problem is that there may be slight errors on that disc, noise you do not hear when you listen to it but that will show up on a copy. Even if there are none now, they may develop over time or with handling and they may show up when you upgrade to a drive that doesn't like the medium you used. The key here is that when you save as audio, you gain about 13% in capacity but pay for that by dropping a layer of error correction. The odds are that you'll be okay, but you can hedge your bet with one of the other options.
Okay, if you save the WAV files, you get back that blessed layer of error correction and gain extra confidence. Unfortunately, you lose 13% of capacity, so that if you started with a 74-minute disc, you need to store about 740 MB and ECC or not, it won't fit onto one disc. You could write it to two discs, which makes re-creating the CD-DA tedious; you could use a "99-minute" blank, but that will run the risk of failure 'way up. So if your home-made disc is less than about 65 minutes, you're home free, but otherwise you have your choice of poor options if you want to save as WAV.
It turns out that this has the same size problem as saving WAVs with little advantage. For example, if you decided you wanted to touch up a track, you would have to extract all the tracks to WAV, modify one, then make your new CD-DA and a new image to save. Extracting those tracks can mean burning a fresh CD-DA and running DAE or running a program such as CD-R Diagnostic or ISOBuster. The one advantage of archiving as an image is that it lets you make additional CD-DAs very easy: just double-click the saved image to fire up the appropriate mastering program, ready to burn.
Compressing to MP3 or one of the other formats using perceptual encoding can give you back that 13% - and a lot more. Many people are happy with redbook audio compressed to 128 Kbps - a factor of eleven or so. Some want to cut their losses and use 256 or even 384 Kbps. Even so, there are losses and at the least, they may leave you wondering whether you've thrown away something you will want some day. It's also worth noting that high-quality compression, such as high-rate with LAME, are far from speedy.
"Lossless" compression? What's that about?
Typically, a WAV file compressed without loss is about half the size of the original, regardless of the audio compressor used. In all cases I've encountered, that means that one can easily put the sound, booklet and related material from one CD onto a single CD-ROM and still have the advantage of the extra layer of error correction. The drawback is, of course, that the resulting disc won't play in your stereo but only in your computer. So files with lossless compression are fine for archiving, but not for convenient listening.
We know that the usual compressors - ZIP, RAR and the like - do little or nothing to save space in a WAV file. But there are compressors for audio which cost neither quality nor money. The one I've run is Monkey's Audio, which is quick, simple and provably lossless. That is, you can take your favorite WAV file, compress it to APE, then decompress it and you will have a bit-for-bit match to the original. Because lossless compression throws nothing away, it does not shrink files as much as MP3 does, but it will save more than enough space to put even an 80-minute CD-DA onto a 650-MB disc. The one drawback is that you must decompress back to WAV to use the file. If one of the schemes becomes popular, perhaps the CD-mastering programs will accept it for direct writing.
The time you spent creating this audio masterpiece is worth a fair amount to you; don't sacrifice it for a few pennies of medium. Testing labs which have the equipment and no bias will tell you that the longer the blank, the higher the error rate. That doesn't mean that you will hear the difference - even if CD-DA loses one layer of error correction, there are others beneath it. What it does mean is that a 90 or even an 80 is less reliable than a 74 and that you run a higher risk of having an error when you need that file. This is also a case where you may want to invest the extra dime or dollar in a Taiyo-Yuden or Mitsui disc - the best you have found for your writer - just to be sure.
Links to the programs in this page are here at this site.
E-mail me at cdrecording@mrichter.com
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