A Beginner's Guide to Burning CD's

Reprinted with permission Canadian Music Educator’s Journal, 41(1) 6 – 12 (2000) A Beginner's Guide to Burning CD's Geoff Martin this latter point is largely the result of the CD-ROM market, it means that musicians are able to produce their own CD's in low volume for demo recordings and auditions at a cost that rivals or even undercuts duplicating on cassette. 1 - Introduction The original working title of this article was "So I Bought a CD Burner but How Do I Get My Choir On It?" Speaking as a recording engineer, my first answer is of course "Hire a recording engineer!" This however, is not an option for many people, due either to cost considerations, driving independence or bad previous experiences. The intention here is not to teach anyone how to make a perfect recording destined for a nomination at the next Grammy Awards. The intention is to arm you with enough information to avoid common pitfalls that exist between having an ensemble that you wish to record and listening to a recording of that group on a homemade CD. In 1983, a magazine advertisement introducing the new compact disc format proclaimed "Perfect Sound, Forever." Although there are few people today who would agree with either of the two claims made in this statement, there remains no question that the introduction of digital audio to the consumer market marked an enormous leap in the sound quality of media accessible to the general public. The compact disc was not only the first medium which ensured that the audio quality of the consumer distribution format was identical to the recording systems used by professionals, it was the first format which did not degrade as a result of repeated playing. Sony and Philips originally designed the CD to be used for audio distribution, however, since the format is used on a fundamental level to simply store a series of binary digits, it can be used to distribute any other digitally encoded data. This compatibility with multiple platforms such as audio, graphics and video players in addition to computers has had a number of impacts on the market. First, the cost of producing a single disc has dropped significantly since the introduction of the format (despite the relative lack of change in the prices on the record store shelves...). Second, the ability to record material on recordable CD's, also known as CD-R's, has finally come within reach of the average consumer. Despite the fact that 2 - Choice Of Venue And Your Location Within It The quality of the acoustics in your performance space is one of the most significant contributors to the ultimate quality of your recording, second only to the level of the performance. Having made that statement, we have to discuss the issue of what makes a particular space appropriate for recordings. There are a number of components of the acoustical qualities of a room which determine its usefulness for musical performances. 2.1 - Noise Noise can be generally defined as any sound that occurs in the room which doesn't have anything to do with the performance. This problem can be the result of either sound sources outside or inside the room. The objective is to find a space which is completely quiet. In order to eliminate contamination from outside noise sources such as traffic and airplanes, the modern concert hall or recording space is built as a floating "box" within a larger isolating box. For example, when you walk into the CBC Toronto's Glen Gould Studio from the street, you'll notice that you cross over a rubber gasket which separates it from the rest of the world. In fact, the whole room sits on rubber blocks which ensure that the rumble of the surrounding city is not transferred into the hall. By comparison, one of the nicer concert halls in Montreal was originally built as a library for McGill University in the late 1800's. The weakest link in the structure isolating the inside of this hall from the noise of downtown Montreal are single panes of stained glass. Needless to say, this is a rather inadequate environment for quiet recordings, particularly on Friday nights... Noise from inside the room can be the result of things such as air conditioning, buzzing fluorescent lights, and in the case of live performances, coughing audience members, and candy wrappers. Just before your session, request that the members of your ensemble turn off their digital watch alarms, remove change from their pockets and, temperature permitting, take off their shoes (I frequently suggest for recording sessions that people bring an extra pair of wool socks). your brain decides that it's simply the ambient sound surrounding you. Different amounts of reverberation (usually specified as a period of time such as 1.5 seconds) are appropriate for different styles of music. Choirs and brass quintets usually benefit from long reverb times found in old stone churches. Small string and woodwind chamber ensembles require an increased clarity found in shorter reverb times. The reverberant field can also be described in terms of its timbre. If the room is made of very hard, reflective surfaces such as tile, the reverberation will be long but also bright, containing a great deal of energy in the high frequencies. Generally, the more absorptive the surfaces, the more high frequency energy is absorbed and the warmer the reverb. One last consideration which affects both the reverberation and the early reflections is the shape of the walls. Sound bounces off of surfaces in much the same way that light reflects. A very flat surface is to sound as a mirror is to light - the more protrusions and cavities in a reflective surface, the more scattered the reflections (something acousticians call "diffusion"). Essentially, a room made of large flat walls is the acoustic equivalent of a room with mirrors on the walls. This is decidedly not a complimentary environment. The more surfaces which break up the reflection, the better things sound. This is not only why old churches which are full of pillars and statues and irregular stone walls sound infinitely better than a school gymnasium, but also why a room full of furniture sounds better than an empty one. 2.2 - Can the group hear each other? Irrespective of how good the space sounds to the audience (and therefore, to some extent, to the microphones), if the ensemble is unable to hear within itself then the quality of the performance will suffer. There are a number of features of a space which can determine how well the performers hear other people on the stage, but they all involve the use of reflections. Just like light, any time a sound wave meets a surface, it will either be absorbed or reflected. Surfaces such as concrete, stone, wood and plaster generally make excellent reflectors, while curtains, carpet, padded chairs and people act as absorbers. It has been shown that musicians within an ensemble, particularly a large one such as a choir or orchestra, can benefit from strong reflections in the stage area. These can come from side and rear walls or from the ceiling, however, they must be received by the listener within approximately 30 ms (milliseconds) of receiving the sound directly from the sound source. (A good rule of thumb is that sound travels about 34 cm in one millisecond - therefore the reflective surface should be less than about 5 m away.) If the reflection arrives later than 30 ms, then it's perceived as a discrete echo rather than being a component of the original sound and isn't of much help either to the performers or the recording. Some spaces intended for music performances will either have reflecting walls or a "shell" surrounding the stage area. This can be assisted by reflecting "clouds" which are panels hung over the stage giving the acoustic equivalent of a lower ceiling over the performers. 3 - The Equipment 3.1 - Microphones The next most important choice which affects your sound quality and presentation is the choice of microphones. These come in all sorts of shapes and sizes but can be chosen based on two basic characteristics: the method by which they produce a signal and their directional characteristics. Microphones can be designed to produce electrical signals from an incoming sound in two ways. The first of these, called a dynamic microphone, is the one you most commonly see in PA systems. This is largely because dynamic microphones are both rugged and fairly inexpensive (good dynamic mic's cost about $200 brand new). The problem with using these microphones for classical recording is that they do not usually exhibit a good "frequency response." This is basically a measurement of a device's ability 2.3 - Reverberation The last major issue in a larger room is the question of reverberation - better known to many as "echo." This is essentially the collection of reflections off the various surfaces in the room which arrive at the listener so close together that you're unable to distinguish them as individual sounds, and therefore to faithfully reproduce the timbre of a sound source. The second type of design is called a condenser microphone. This is a much more accurate and sensitive device but is also a great deal more fragile and more expensive. (Typical prices for a condenser microphone run from about $1500 to as much as you'd like to spend.) In addition, most condensers require an external power source called phantom power which should be provided by your mixer or microphone preamplifier. In the case of classical recordings, there is simply no choice but to use condenser microphones for your recording in order to achieve an accurate reproduction of your ensemble's sound. You may have a problem finding a rental company which can offer you a pair of condenser microphones. See the Table 1 for a suggested list of microphones. Rental costs for these devices typically start at about $25 each per day and go up to roughly $100. The directional characteristics of a microphone influence a number of decisions regarding microphone placement and technique as well as the overall balance of the ensemble. As a general rule, omnidirectional microphones are better able to reproduce very low frequencies (such as bass drum or organ pedals) than directional (cardioids or bidirectional) microphones. On the other hand, this also means that they are better able to reproduce lowfrequency noise such as internal air conditioning and external traffic rumble, so they are not necessarily the correct choice in all situations. background knowledge. The first standard technique for recording classical music called the XY configuration. This is an arrangement where the capsules (the pickup end) of two cardioid microphones are vertically aligned, the microphones are at 90 degrees to each other and their bisecting angle is aimed at the centre of the ensemble. (see Figure 1). For a more "spacious" sound, it is effective to slightly space your microphones. There are a couple of European broadcasting agencies which suggest configurations such as 110 degrees and 17 cm apart at the capsules (ORTF configuration) or 90 degrees and 40 cm apart (NOS configuration). Any of these arrangements will work - but consider them to be starting points from which one can spend the rest of one's life searching for the right combination. Keep in mind that there is no single configuration which will work perfectly in every situation. Microphone technique, like spices in cooking, depend entirely on tastes and moods and will change according to venue, musical style, and instrument. The next question is where to put the microphones. Generally, a good rule of thumb is to put them just behind the conductor, and far enough up so that you don't hear too much noise from the arm-waving below. If, when you listen to the resulting sound in your loudspeakers, there is too much reverb (things sound too distant or "washy") then move the microphones closer. If things sound too close or completely lacking in the room sound, back them away or move them straight up. 3.2 - Microphone Technique Finding the appropriate configuration and placement of the microphones in the room is a holy grail in the world of recording engineers and producers. There is no stock answer to the question of either. I recently read a question posed to an Internet newsgroup asking where the best place was to place a microphone to record a french horn. The wisest response I read was "asking where to place the microphone to record an instrument is like asking where to stand to take a picture of a mountain." There is no correct answer. Every instrument, every room and every musical style requires a different technique which should be chosen according to the circumstances. Obviously, this decision has to be made using a great deal of experience in experimenting with different techniques in various situations, however, there are a number of "textbook" configurations which can be used as starting points. These will offer you a reasonable presentation of the ensemble without requiring a great deal of 3.3 - Microphone Preamplifiers and Mixers The output from your microphones must be amplified to a level high enough to be compatible with your recording device. This can be done using either a mixer or a dedicated microphone preamplifier. It is usually cheaper and of comparable quality to use the former. Assuming that your microphones are condensers, you will require a mixer which has a phantom power supply. This is a 48V DC supply in the mixer which is used to power the microphones and is "sent" to the mic via its microphone cable. One particular unit which is highly recommendable is the Mackie 1202 VLZ mixer (www.mackie.com) which has a total of twelve inputs (four of which accept phantom-powered microphones) and a stereo output. The primary reason for this choice is the quality to cost ratio. These are extremely dependable compact mixers which cost on the order of $500 - rental costs should be approximately $10-$20 per day. 3.4 - Recording Devices The output of your mixer goes straight to the recording device which should be a DAT (Digital Audio Tape) recorder such as the Tascam DA-30 or DA-40 (www.tascam.com). You will have a choice of sampling rates on this device - either 48 kHz or 44.1 kHz. The correct choice is 44.1 kHz in order to match the sampling rate of the CD you will eventually be burning. A very good option to replace both the mixer and the DAT machine is the Tascam DA-P1 which is a portable DAT recorder with microphone inputs and phantom power - the only problem here is finding one available for rent. 3.5 - Monitoring You have two options for monitoring the results of the recording during the session. In order to get an accurate representation of the imaging of the final product, you have to set up a pair of loudspeakers with a power amplifier. If you're not really interested in dragging around a heavy pair of speakers, you may prefer to use headphones. There are a couple of things to remember with headphone reproduction that can cause you difficulties. First, the left-right range of the imaging in headphones is exaggerated - so instruments will appear to be on either side of your head when, in loudspeakers they do not necessarily appear on the hard left and hard right. Second, the reverberant field in headphones appears to be lower in level than when you're monitoring in loudspeakers due to your brain's ability to focus on sound sources better. The basic result of this is that, when you place your microphones based on what you hear in headphones, instruments will appear to be too distant when the recording is played back over loudspeakers. There is an Input Level control on the DAT recorder which will also require some attention. If you have experience recording on analog tape such as cassette or open reel, you'll know that the 0 dB marking on the meters on these older devices is simply a reference point which can exceeded when the musical signal is at its loudest. This is not the case for digital formats such as DAT and CD. You must set the input level of the DAT machine such that even the loudest section of the music is lower than 0 dB on the meters. On most machines, there will be an ongoing display which shows the maximum level reached (usually called the "margin") If you reach or exceed 0 dB, this display typically will flash to warn you that things are just too loud. If you do hit 0 dB during a take, you've ruined the recording - you must interrupt your musicians and politely request that they start the piece again (remember to turn down the level slightly before re-starting). 5 - Editing It is not an exaggeration to say that virtually every commercial recording made in the past 30 years has relied on some form of editing to "improve" the quality of the performance. This is particularly true today where we typically see something on the order of 500 edit points (the current term for "splices") on a classical disc. In the days of Glen Gould, razor blades were used to cut sections of analog recording tape which were subsequently reassembled. This procedure has been supplanted by sophisticated computer-based hardware/software packages which are capable of fading from one take to another almost completely inaudibly. The problem with using a digital editing system is that it requires a great deal of experience and technical knowledge. If you do require some editing to be done, I would suggest that you seek out an individual or studio with a system such as the SonicSolutions or SADiE editing packages. Prices for these systems usually run approximately $25 per hour for the studio and at least $25 per hour for an editing engineer. To get an idea of how much to budget for editing, professional editors can accomplish between 12 and 15 edits per hour. If you would like to try some editing on your own, two good entry-level editing software packages are "Peak" for Macintosh (a demo version can be downloaded from www.bias-inc.com) or "Sound Forge" for PC's (www.sonicfoundry.com). Of course, the better solution is to avoid editing altogether by either having a well-rehearsed group or by lowering your standards... 3.6 - Setting the correct levels In a simple recording setup, the level of the output of the microphones can be controlled in three places on the mixer, the Microphone Gain, the fader of the input strip, and the Master Output fader. Each of these should be set according to some simple rules. The Microphone Gain should be set such that the loudest section of music for the entire recording should be just below lighting up the Peak light on the input strip. The best way to ensure this is to request that the musicians play the loudest section and set the Gain to cause the light to flash - then back the Gain down slightly. Assuming that you are only using two microphones, the Fader and Master Output levels should be set to 0 dB - this means that they are not changing the level of the signal, so all of the amplification is coming from the Microphone Gain. 6 - Mastering Before committing your recording to a "permanent" format such as a compact disc, you will require that the final product is mastered. In a professional situation, this is the equivalent of putting the final coat of polish on a piece of fine furniture before it leaves the workshop. In the case of a demo recording, this is relegated to a function better labeled "dubbing." To begin with, you will have to transfer your recordings to the hard drive of your computer. In order to avoid degrading the quality of the recording, it is best if this is done using the digital output of the DAT recorder connected to the digital input of the computer. Unfortunately, unless you've spent an extra $1000 or so on an audio card for your computer with a digital input, you won't find the required connector. A highly recommendable audio I/O (Input / Output) device which is compatible with both PC's and Macintoshes (equipped with a PCI card slot) and multiple recording devices is the Mark of the Unicorn 2408 (www.motu.com). In addition to being a digital audio interface, it includes a piece of software which will permit you to use your computer for digital multitrack recordings. If you're looking for a simple stereo card or device which will allow your computer to communicate with a digital audio signal, look for anything that has either an S/PDIF or AES/EBU connector. These are the standard protocols for almost all digital audio devices. In a simple mastering process, you basically want to do four things: 1. "Fade in" to and "fade out" of each track to get your piece from complete silence and back smoothly. This is done to avoid any nasty clicks at the beginning and end of each piece. 2. Make sure that the levels of the various tracks are matched. There's nothing more annoying than having to turn up and down the volume throughout a CD because the tunes are at different levels. This is fixed in the mastering stage. 3. Put the tracks in the order you want them to be in on the disc. 4. Put the appropriate amount of space between the tracks. The standard for this space is 4 seconds, however, you may wish to change this according to your requirements or tastes. One important thing to keep in mind before setting out on mastering your disc is that you will be transferring the audio from the DAT to your hard drive as an interim storage device before burning the disc. This means that you'll need lots of spare space on the hard disk - just under 10 MB per minute of stereo audio in fact... The CD-R can store up to about 70 minutes of music, giving it a total capacity of about 650 MB. 7 - Burning CD-R's Once the mastering is done, all that's left is to actually burn the discs. This is usually done using the same software that you'd use to do the mastering. The software "talks" to the CD-R burner and writes all the appropriate extra information regarding the different tracks on your disc. There are a number of different software packages which can do this for you, ranging in price from about $100 to $40,000, depending on your needs. Chances are that, for most projects, the cheaper packages will do nicely. There are a couple of "standard" entry-level packages made by Adaptec which suit most requirements. These are "Toast" and "Jam" for the Macintosh and "SoundStream" and "Easy CD Creator Deluxe" for the PC (all from www.adaptec.com). If you're buying any of these, make sure in advance that they will recognize your CD-R drive. (Many retailers will include Toast and Easy CD Creator in the purchase price of a CD-R drive.) 8 - Care And Feeding Of CD's And CDR's Despite the fact that most people treat their CD's better than they do their fine china, this isn't really necessary. CD's generally can withstand a great deal of abuse before becoming unplayable. Their shiny appearance is merely a front for an otherwise robust medium. CD-R's on the other hand, are considerably more fragile - some more than others. Look for CD-R's which have a top coating which appears to be painted rather than metallic. The problem with the latter (such as the gold-coloured TDK's) is that the metallic surface is the same material which is burned by the laser. If you scratch it, you lose your disc and turn it into what professionals frequently term a "coaster" because that's about all it's useful for anymore. The moral of the story here is to take good care of your CD-R's. Don't leave them in the sun (even if they're just sitting in their cases on your shelf and the sun happens to be shining in), don't clean them too often, and if you can avoid it, don't write on their surfaces. 9 - Rival And Future Formats There are a number of other formats which are either available or will be available in the near future. The first of these is MiniDisc which more and more musicians are buying for personal recordings. This is followed quickly by the growing use of MP3 (more formally known as "MPEG-1, Part 3"), particularly in Internet distribution. Both of these formats are, by design, inferior in quality to CD in spite of everything you've seen or heard in advertisements. They are based on data reduction (not data compression) schemes which attempt to determine what you are not able to hear in the music and throw it away in the recording process, therefore requiring less information to be recorded. There are many problems associated with these procedures, including the production of "artifacts" (extra, unwanted noises like "chirping" sounds) in the playback, and uneven decays in reverberation and instruments such as cymbals. Keep in mind that these formats are, at best, to be considered replacements for the cassette, which was originally developed as a dictaphone machine, not for the recording of music... A format which is intended to replace the Compact Disc is the DVD or "Digital Versatile Disc" (not "Digital Video Disc" as the digital video producers would have you believe). There are many different standards for the audio quality on DVD's, depending on the usage. In the case of a movie soundtrack with accompanying picture on the DVD, the audio quality is lower than a CD due to the use of a data reduction scheme known as "AC-3" from Dolby Laboratories (www.dolby.com). This is the standard data reduction used on all DVD-based movies as well as the sound you're listening to in a Dolby Digital theatre. Thoughtfully, the DVD was designed to support much higher audio qualities up to five independent channels of what is known as 24bit/96k (denoting two measurements of the resolution, the number of bits and the "sampling rate" of the audio on the disc see the glossary below for more information) which winds up being about 8 times more information per second than a CD. As a result, DVD's have a much greater capacity than a CD - on the order of about 8.5 GB (as opposed to CD's 650 MB). artistic requirements of typical professional recording, editing and mastering sessions are fraught with excruciating minutiae, any of which can result in a ruined recording. It would not be advisable for a novice to attempt to produce a commercial-quality recording without some professional assistance or at least advice. Start simply, with low expectations for the production quality of your early projects. With some practice and attention, however, you should be able to consistently produce recordings which will provide an accurate and esthetically pleasing representation of your performances. 11 - Glossary Bits - the resolution of a digital audio medium's measurement of the signal. This is equivalent to the number of divisions of an inch on a measuring tape. The higher the number of bits, the higher the accuracy of the system - and therefore the less distortion of the original waveform. The standard for CD's and DAT is 16 bits. With a couple of notable exceptions for DAT, this is a limitation of the carrier media and cannot be exceeded. Bit resolutions are a case where the basic "more is better" rule applies with one exception being systems which have only 1 bit. The quality of these systems may be able to outperform systems with higher numbers of bits depending on the manufacturer and application. CD-ROM - An acronym for "Compact Disc - Read Only Memory" - this is a generic term typically applied to CD used for the storage of computer software, however it includes a number of different specifications. DAT - Digital Audio Tape. This is a format which was originally intended to replace cassettes in the consumer market, however it was quickly adopted as the standard stereo format for professional digital audio production. Its audio quality is identical to a compact disc. On of the largest advantages of this format over its predecessor, open reel tape, is the cost of the media. Professional stereo analog (open reel) tape costs approximately $1 - $2 per minute of music. DAT's usually sell for approximately $15 for 2 hours of recording time. Imaging - the perception of the placement of sound sources and the reverberation in a stereo or surround sound reproduction. This usually applies to only the left-right location of the sources. Millisecond - one thousandth of a second MPEG (or MP3) - a system used to reduce the 10 - Conclusion Not unlike a musical performance, the technical and amount of data required to transmit a digital audio signal. This is essentially a software system which is able to predict which components of the music you are unable to hear (because they're being drowned out or "masked" by another sound) and then omits them from the recorded signal. The correct pronunciation is "EM-peg." (http://drogo.cselt.stet.it/mpeg) Red Book - This is the book (yes, the original had a red cover) which contains the physical specifications for the manufacture of compact discs as well as the details regarding how digital audio is encoded to be stored on an audio CD. There are other such "books" for the other CD formats - Yellow for CD-ROM, Orange for CD-R, Green for CD-i, Blue for Enhanced CD and White for Video CD. These all use the same physical specifications detailed in the Red Book but include standards for the various data encoding methods. These various books are required by manufacturers to ensure compatibility from machine to machine. These books are all available from the International Standards Organization (www.iso.ch). Sampling rate - the resolution of a digital audio medium's measurements in time. This is an equivalent of the frame rate of a motion picture. The higher the sampling rate, the higher the frequencies you are able to record. The standard for compact discs is a sampling rate of 44.1 kHz (or 44100 samples per second). 12 - Suggested WWW Sites for More Information www.cdpage.com An excellent source of basic information on the CD and DVD formats and related issues. www.josephson.com/mictech.html The beginnings of a collection of information on microphone techniques. www.tonmeister.ca The beginnings of an online textbook for sound recording techniques including information on electronics, acoustics, and recording techniques. Table 1 - Suggested list of microphones Cardioid Omnidirectional Switchable pattern Approximate Rental Cost (each per day) $15 - $25 Shure SM81, AKG 451, AKG Blue Line CK91, Neumann KM184 Sennheiser MKH40 Bruel and Kjaer 4011 AKG Blue Line CK92, Neumann KM183 Sennheiser MKH20 Bruel and Kjaer 4006 AKG 414, Neumann U87, Neumann TLM 103 $35 - $50 Figure 1: Textbook microphones configurations