One of the functions many people seek with CD-R is creating audio CD's. Software for creating CD-ROM's supports that desire, but each product varies in the ways in which the job is done. For information on your software - read the manual. This note is intended to cover the basics of audio file formats and problems.
Jump to Recording with D/A/D conversion
Editing a WAV file
Recording on the fly
A selection on an audio CD is very nearly in WAV format. It is a variant of a specific type (redbook) of WAV file: 44.1 KHz sampling, stereo, 16 bits depth. Unlike an ordinary data file on a CD-ROM, the sound file does not contain error correcting codes (ECC) within it to handle data lost in transfer. Instead, a layer of ECC is provided on the disc. One of the ways in which CD players vary in sound quality is that they are more or less effective in using ECC to repair errors in reading the audio.
NOTE that an audio player is required to read only the first closed audio session on a disc. To avoid problems of poor readability, mysterious noises and so on, the beginner should not try to leave the disc open when closing the first audio session. You may write the disc in DAO, write the whole session at once in TAO, or write repeatedly leaving the session open until the last track, when you should close the disc. When you understand CD Extra and are willing to experiment, multisession can be fun.
There are two different ways to create a file on a CD-ROM: an audio CD track or a WAV file. Only the former will play in a CD player. However, CD-R software will convert a WAV file (CD Creator will take one at less than redbook standard) into the necessary format and will read the audio file from a CD into a redbook WAV file on your hard disc. In that process, your reader may run at anywhere from 1x to its maximum speed. The higher the speed of reading, the more chance that some information will be lost. Since there is no effective error correction, those faults will show up in the WAV file. Fortunately, that file is on your hard disc and you can listen to it. If it sounds good there, it should sound good when converted to the CD format and recorded. If the copy on your disc has clicks or other problems - don't give up.
The first step is to persuade your software to read the CD at a lower speed. First, you need a player which supports Digital Audio Extraction (DAE). Your CD-R certainly will do that; a CD-ROM reader may or may not. Most SCSI readers provide DAE; very few IDE readers do, and then only with the right software. If your reader does not support DAE, you can use D/A/D conversion or your CD-R. Let's assume we have DAE. Using whatever tools your software provides, cut the read speed down until you get a clean WAV file. That tells you how fast you can run with that CD. Now check with other CD's to find out whether your first one was unusually good (or bad). Ultimately, you will decide that you can use a particular speed reliably. Don't try to cheat on it: If your reader won't give you a good signal at 4x, no software or CD-R media or whatever will improve on that.
Note that you are now beginning to understand why some 8x CD-ROM readers are slower than some 4x. They may run at 8x under ideal conditions, but if they aren't able to retrieve information reliably, even error correction may not be enough to get a good file. So the system rereads that file until it comes out right. There's no standard around to say what 8x (or any other speed) means - except that under some circumstances as many as 8x150 KB/sec will come from the drive. Whoopee!
The information on a CD or CD-ROM is stored in digital format. To listen to that signal, it must be converted to analog (a.k.a. analogue to us old-timer purists). The conversion is done in the reader and uses the ECC of the disc to a greater or lesser extent. If you have put an appropriate jumper from your reader to your sound card (so you can listen to a CD while you 'work'), you can record from that with controls on your mixer. If not, any CD player can be connected to the Line In jack on your sound card - as can any other appropriate source of analog audio. The quality of the signal going into your sound card then depends on the quality of the CD reader/player you are using.
On the sound card, an analog signal is converted to digital - and with that comes a set of problems. Essentially, converting between analog and digital signals is a matter of approximation. D/A is hard enough, but A/D is tougher still. The result is that only very good and very costly equipment will do first-rate D/A/D. Is your present sound card good enough for you? No one can answer that but you. Would the BrandX SuperSound do enough better to be worth the cost? 'Better' depends in part on your taste, and 'enough' is meaningless to anyone but you. Perhaps someone on the mailing list or in a newsgroup can give you insight, but don't expect easy answers. There aren't any.
At least, if you do use A/D/A instead of DAE, you will use the CD's ECC. If a CD you want to use insists on crackling on DAE at 1x, you may have no other choice.
One of the advantages of making a WAV file through DAE or D/A/D is that you can edit it. Tools for that purpose are included in the audio section of the links at this site. Those editors will let you modify the sound in many ways: denoising, adding effects, repitching, cloning, ...
There are some tricks to this operation. One is that some software figures that whatever's tucked onto the end of the file for its own purposes won't do any harm. As far as the computer is concerned, that's so. However, on a CD those bytes become a 'click', and for some strange reason most people don't like extra clicks and pops on their recordings. Here, the solution is easy: don't end your editing with such a program. If you want to use an editor which you know leaves the click behind, do it. Then open the file in another editor that you know doesn't make popcorn (such as GoldWave) and save it. The click will be left behind.
"On the fly" means writing the CD-R from the source (here, a CD reader) without going through the extra step of writing to the hard drive. Let's dispose of the obvious first (not that you don't already know it, but for the benefit of those who don't). You cannot read from the CD-R while you are writing to it; therefore, you need a separate CD reader to record on the fly. Recording on the fly requires that the data being read are digital, so your separate reader must support DAE. If you don't want to use a second, DAE-capable reader, you cannot record audio on the fly. Given current prices for a SCSI CD reader under $100, it doesn't take many coasters to pay for a second drive - and you have a SCSI adapter already for your CD-R, so you probably don't need to buy one of those.
When you go to record on the fly, your software assumes that you can run at full writing speed without a problem. So you're tempted to think that your CD-R that writes at 2x will work fine with a reader that runs at 2x or above. You may be disappointed. For audio, you should already have determined with the WAV tests above that your reader is only reliable at 1x - even though the box says 2x, 4x, or 45.7x. The same thing that keeps a WAV file from sounding good will guarantee ticks and pops when you record on the fly. Therefore, you must slow down on-the-fly recording to the highest speed at which your reader will work. Of course, if that speed is faster than your CD-R can write, you can't beat the CD-R hardware by getting a faster reader. There's still no free lunch.
Recording a CD is much like recording a CD-ROM. Some combinations of media, hardware, firmware and software work better than others. If gold/gold media work better for you for CD-ROM, they will probably be better for CD, too. Just because your hardware vendor's bundled software has a good interface for CD-ROM does not mean that you will find it ideal for audio (or vice versa). There are at least three choices of CD-R software on each major platform and each does every part of the job differently from every other.
There is no 'best' hardware, software or medium. The mailing list and newsgroups will provide you with unauthoritative, inaccurate, contradictory, incomplete and irrelevant information. Still, it's better than buying and learning all those products.
At least I think it's better.
From: Bart Lynn - blynn@eng.jvcdiscusa.com
As an Engineer for a CD manufacturer, I feel that I can try to explain the differences in the pause times on CDs. Red Book (the Compact Disc Specification for Audio ) states that the Pflag must be 2 ~ 3 seconds. Therefore, since Absolute time starts at 00:00:00, the start of track 1 can be from 00:02:00 to 00:03:00. Of course, there can be silence after that point, so there can be in essence a lot of pause.
Most PC/Mac software sets the start of track 1 at Atime 00:02:00, since Yellow Book (Compact Disc Specification for normal CD-ROM discs) specifies that the pause be just 2 sec. At JVC, we start at 2 seconds Atime, then we offset the first track 1 second, prior to the start of the music (CD-ROMs start at exactly 00:02:00). Each additional track is offset 5 frames (30 SMTPE frames to 1 second). The end time of the last track is moved forward 1 second. The reason is that many old CD players (from like 1985, up to the triple beam ones) search for the start of the track by the Pflag, not the absolute time. The new players can be extremely accurate in searching, where the older ones cannot. As a manufacturer, we have to try and supoort all makes and models, so we have to provide a slight tolerance for them. Additionally, the record label/artist sometimes requests that we provide additional pauses, especially for classical music, or live recordings.
Bart Lynn
JVC Disc America
Extensive additional material is available at http://www.westnet.com/~gsmith/ - but let me caution the unwary that the subject is complex. Those pages may be difficult to digest, but can be worth the effort.
E-mail me at cdrecording@mrichter.com
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