


RECORDING COMPACT DISC DIGITAL AUDIO 


Recording audio compact discs, also called "Red Book discs" or "CD-DA" discs
is a popular subject these days.  With the advent of the new generation of low cost
CD-R drives, more and more people are getting into "rolling their own" audio discs.
Firstly, I'd like to point out that you should take care not to infringe on the copyrights
of others when creating audio discs.  Frequently, users want to make custom discs with
tracks from their favorite albums.  This is illegal; you shouldn't do it.  The information 
presented here is intended for legitimate applications.

So, why would you want to produce audio discs with a CD-R drive?  If you are a recording
studio, have a home studio, are a musician, or are a producer; the reason is clear.  Recording
studios, by and large, still give their clients a cassette tape as a reference.  As we all know,
tapes sound grungy compared with compact discs.  In this case, the client won't know how
the music will sound on CD until discs are pressed.  If a change is needed, say in EQ, then
the disc must be pressed again.  This is very costly in terms of time and money.  If the
studio could give the client a one-off CD as a reference, changes can be made quickly and
at minimal expense.  If you are a musician and you want to send your project to a label or
even to a radio station for some free air time, a compact disc lends some credibility.  How
many cassettes do you think a major record label receives for consideration?  Now how many
compact discs do you think they receive?  See the advantage?  They are more likely to 
listen to the CD.

Since most CD-R drives are computer based, I will cover the ways your computer can be
used to cut a audio CD. 

Sampling - Direct to hard disk recording

The most basic approach is using a sound board with a compact disc player, or tape player;
and a compact disc recorder (CD-R).  Most contemporary sound boards can sample at
44.1Khz. at 16 bits.  What does that mean?  The sample rate is simply how many samples
the sound card takes in 1 second of the signal you send into it's inputs.  44.1Khz. means
that the sound board takes 44,100 samples per second. 16 bits is the resolution of the sample,
or, how deep it is.  In both cases, sample rate and resolution, higher is better.  The higher
the sample rate and resolution, the better the quality of the sound.  Use 44.1Khz/16-bit when
recording audio for compact discs.  Connect the CD player or tape machine to the line input
of the sound card.  Follow the directions for the sound board software to start recording, and
send the audio you want to record into the sound card's inputs.  This will record the audio
to the hard disk, usually in the .WAV format for Windows (AIFF or Sound Designer II for
Macintosh).  Check to be sure that your CD-R software supports the file format your sound
card uses.  Generally, you will need a hard disk with a access time of 15ms or less to do this.
Also, keep in mind that at 44.1Khz./16-bit, you will need 10Mb of disk space per minute of
audio.  The average song is 3.5 minutes; that's 35Mb of disk space!  When you are finished
recording, you can check your recording by playing back the sound file now present on your
hard drive.  When you are ready to make a CD, follow the CD-R software directions to cut
the disc.  This approach is okay for many people, but is really not the best.  Most PC sound
cards have, at best, mediocre analog to digital (A/D) converters.  On top of that, all the RF
(radio frequency) energy that bounces around inside a PC can cause all sorts of unwanted
artifacts in the sound (pops, clicks, ect).  In my experience, the sound cards that produce the
best sound quality are made by Roland and Turtle Beach.



The second approach yields the best sound quality and is suitable for professional use and
commercial replication.  Digidesign of Menlo Park, CA has been producing hard disk 
recording systems for the music industry for years.  They have several levels of products
that fit all levels of users.  The concept of operation is the same as described above, however,
the quality of the sound is superb.  For the PC, the best product is Session 8.  For Macintosh,
the best system is Pro Tools.  In addition, Digidesign offers accessory programs such as
MasterList CD for cutting audio discs with CD-R drives.  If you want to sync sound to
video, Digidesign offers PostView.  This is the best solution, in terms of sound quality
and integration.  These systems are surprisingly affordable!

Transferring audio in the digital domain

What if you already have a CD with your audio on it and you want to transfer it digitally
to your hard disk for editing?  Or what if you have several sound effects discs and you
need to take a track off each one for a special compilation?  There is a way to accomplish
this.  If you have a PC, get a copy of Incat System's CD Workshop.  If you have a Macintosh,
get Disc-to-Disk from Optical Media International.  With either of these software packages,
your computer, and a compatible CD-ROM drive, you can "bounce" tracks from a CD to your
hard disk.  This bounce is a digital bounce; audio data is transferred digitally from the CD to
the hard disk.  CD Workshop only supports the .WAV file format for audio, Disc-to-Disk supports
.WAV, AIFF, Sound Designer II, Quicktime, and Sound file formats.  Once the audio is on your
hard disk in the appropriate format, you can playback the sound files to check them.  When you
are ready to cut a CD, follow the directions of your CD-R software to produce your CD.

Another digital approach I will cover is when you have DAT tape and you want to get the
audio on your computer in a .WAV format (PC), or AIFF/Sound Designer II (Mac).
Since the DAT (digital audio tape) is already digital, you don't need (or want) to send
the sound through another set of A/D converters.  The key is that the DAT must be 
a regular audio DAT (recorded on a consumer audio or professional audio DAT deck)
recorded at 44.1Khz sample rate.  If the tape is recorded at 48Khz, you will need a 
sample rate converter.  For the Macintosh, Digidesign has a low end audio card with
digital input/out put. This card is called Audiomedia II.  For the PC, Digital Audio Labs
 makes a card with digital I/O called the Digital Only CardD.  With either product, 
connect the digital outputs of the DAT deck to the digital inputs of the Digidesign or 
Digital Audio Labs sound card. There are no level adjustments with digital I/O, just follow 
the directions for the sound card software to transfer the audio digitally to the PC in the correct 
file format (.WAV, AIFF, or Sound Designer II).  The Digidesign cards can do sample rate conversion (48Khz to 44.1Khz.).  There is no generation loss because the transfer was done digitally.


The last digital strategy I will mention concerns the Alesis ADAT digital multi-track recorder,
Digidesign Pro Tools or Session 8, and the Digidesign ADAT interface.  For those of you who
are unfamiliar with the ADAT, it is a 8-track recording system designed around the S-VHS
cassette tape.  The ADAT can record/playback 8 tracks of audio at a time.  It accepts analog or
digital inputs.  Using the Digidesign ADAT interface, it is possible to simultaneously transfer 8
tracks of audio to Pro Tools or Session 8.  If you only have a 4-channel Pro Tools system, you can
only transfer 4 tracks at a time.  Look into expanding your system and check out Pro Tools III!
Connect the optical connector on your ADAT to the Digidesign ADAT interface and follow the
directions of the ADAT interface software to transfer the audio to Pro Tools or Session 8.  Once
the audio is in, it can be edited and bounced down to a regular stereo .WAV file for Session 8,
or Sound Designer II for Pro Tools.  Use Digidesign MasterList or other CD-R software to cut the disc.




COMPANIES MENTIONED


Digidesign, Inc.			Digital Audio Labs			Roland
1360 Willow Rd.		              14505 21st. Ave. #202			7200 Dominion Cir.
Menlo Park, CA 94025		Plymouth, MN 55447			Los Angeles, CA 90040
(415) 688-0600			(612) 473-7626				(213) 685-5141



Turtle Beach Systems		Incat Systems Software			Optical Media Intl.
52 Grumbacher Rd.		1684 Dell Ave.				180 Knowles Dr.
York, PA 17402			Campbell, CA 95008			Los Gatos, CA 95030
(717) 767-0200			(408) 379-2400				(408) 376-3511


Alesis Corporation
3630 Holdrege Ave.
Los Angeles, CA 90016
1-800-525-3747


Written by Bob DeMoulin, Product Manager for Ricoh Corporation's recordable compact
disc products.  

When you  think CD-R, think RICOH!
