Gt-,. { MULTITRACK RECORDING
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Gt-,. { MULTITRACK RECORDING TEACHER UNIT GUIDE NOTES BACKGROUND INFORMATION The process of recording sound to magnetic tape dates all the way back to the 1920s and '30s. The earliest efforts used steel tape, but plastic-based media began to be available in the 1930s. History was made in 1948 when Capitol Records released a recording of two songs by Les Paul. The record was the first to be created with the process of multitrack recording. Working and recording in his home studio, he stacked eight individual tape recorders together and developed a way of synchronizing their playback. This allowed him to perform and record a number of individual parts, one at a time, while listening to the previously recorded tracks. Although Les Paul sold the design concept for the eight-track tape recorder in 1954, it was not until the late 1950s that manufacturers began to seriously develop and market multitrack recording decks. The advent of the analog multitrack tape recorder gave rise to the modern recording studio. During the 1980s digital technology was introduced into the recording process which included digital tape recorders, signal processing and mixing. Today, the entire recording process can be accomplished in the digital domain. Even with the many advantages of digital recording, some musicians still prefer to record using analog recording decks, citing that it produces a "warmer" and "fatter" sound. With technological advancement and lowered costs, multitrack home studios that can produce high quality recordings are now commonplace. The most economical approach is the analog multitrack cassette recorder. These portable four- and eight-track mini-studios record onto standard audio cassette tapes and also include a mixer with a variety of features for recording and mixdown. While fine for creating basic demos in a home or school environment, they lack the sonic quality of their digital counterparts. Affordable digital multitrack recording came of age in 1991 with the introduction of the Alesis ADAT modular digital multitrack recorder. This eight-track, rack mountable recorder allowed the average musician and project studio to enter the world of digital recording for a fraction of the cost of other digital recorders. A number of recorders can be linked together to create 16, 24, 32 tracks or even greater as the need may be. While modular digital multitracks (MDM) are somewhat more expensive than the analog cassette multitracks, they provide CD quality fidelity and are still conSiderably less expensive than larger, professional studio recorders. I MAGNETIC TAPE RECORDING The recording tape used in a tape recorder consists of a mylar backing coated with a layer of iron oxide particles. This iron oxide coating is where the actual recording takes place. During the recording process, the particles are magnetized such that they are realigned into patterns that correspond to the waveform of input signal. Tape Width There are several standard widths of magnetic tape used on different recording machines. Standard cassette tape is 1/811 wide. Reel-to-reel tape comes in a variety of widths: home stereo and profesSional mixdown decks use 1/4" tape, professional multitrack decks employ 1n and 2" tape for anywhere from 8 to 24 tracks of recording. Wider tape allows not for only more tracks to fit on the tape, but also greater track width and greater track separation. Greater track width results in a higher signal-to-noise ratio, since more magnetic surface is available to record each track. Greater track separation helps to avoid crosstalk between tracks, where signal from one track erroneously bleeds over to an adjacent track. The wider tape used in professional analog tape machines is quite expensive though: $150 or more for a single roll of 2" tape. Digital tape decks do not require wider tape to improve signal-to-noise or to reduce crosstalk. Due to the nature of the digital recording process, the tape formats have very little noise and virtually no crosstalk between tracks. There are two tape formats used in the current lineup of modular digital multitrack recorders. Standard VHSvideo tapes are used in the Alesis ADAT deck and the Tascam DA series uses Hi-8mm format tapes. Analog Tape Formats Analog tape decks are set up to record in a variety of ways. Typically, the tape format indicates two issues: the number of separate tracks that the tape machine can record and whether the recording is done unidirectionally or bidirectionally. In a bidirectional system, the tape can be flipped over and played in the other direction. This is the approach of all home stereo machines. Fig. 7-1 Full-Track - records a single track across the entire width of tape in one directiononly~ = Half-Track Stereo - records two tracks on the tape in a single direction for stereo reproduction. This format is generally used for mixdown decks. Quarter-Track Stereo - Records two track stereo in one direction and two track stereo in the other direction when the tape is flipped over. Standard stereo cassette and reel-to-reel machines use this format. Multitrack Formats - Multitrack recording allows recording on numerous individual tracks - from 4 tracks on inexpensive personal recorders up to 48 tracks on large professional decks. Multitrack recording allows one musician to play and record all of the separate parts of a song. This process is called overdubbing. The person records the first track; and then, while listening to that first track, records another instrument or vocal line onto another track. This process can be repeated for as many tracks as the tape machine is capable of recording. Even when recording a live ensemble, multitrack recording is important because each instrument or vocal part can be recorded on its own track. This allows more flexibility for creating proper balance between parts in the final mix. Also, if one musician makes a mistake, that part alone can be rerecorded without forcing the whole ensemble to redo the work. Some tape recorders allow you to switch between different tape formats. For instance, most of the inexpensive portable cassette multitrack units allow you to switch between a quarter-track stereo format and 4-track unidirectional recording. TAPE MACHINE CHARACTERISTICS Tape Heads The tape heads are the components in a tape recorder that carry out the magnetizing duties. In professional machines there are three different tape heads: 1. The erase head erases material that was previously recorded on a tape. 2. The record head records the new input signal onto the tape. 3. The playback head plays back the signal that has been recorded onto the tape. Many of the less expensive tape machines use only two tape heads. The record head and playback head are combined into one dual purpose head. Digital tape recorders such as the Alesis AD AT use a rotary head similar to a video tape recorder, rather than the fixed heads that are used in standard analog tape machines. Tape Speed Some tape machines allow for switchable tape speed. In analog recording, higher. tape speed settings create a better quality recording, but, of course, allow less material to be recorded on the same length of tape. Tape speed is usually measured in inches per second (ips). Standard cassettes run at 1-7/8 ips, while most multitrack cassette decks offer a double-speed option of 3-3/4 ips. Professional reel-to-reel machines allow for even faster speeds, typically 7-1/2 to 30 ips. Most multitrack and higher end stereo decks also feature variable pitch control which allows for fine adjustments to tape speed, thus changing the pitch and tempo as well. I TAPE MACHINE SPECIFICATIONS WOW and Flutter - As the tape travels past the tape heads in an analog deck, slight variations in speed or alignment can occur. These fluctuations, when audible, are called flutter. Also, the tape may become slightly stretched at times when passing the tape heads, which causes a slight variation in pitch of the sound. This is known as wow. Measurements of wow and flutter are used as standard specifications in rating analog tape decks- the lower the percentage of wow and flutter, the better it is (e.g., ±0.08%). Wow and flutter can be a fairly annoying problem on analog cassette decks. They are much less prevalent in analog reel-to-reel decks because of the wider and heavier recording tape used. Wow and flutter are not an issue in digital recording. Frequency Response - Frequency response is a measure of the range of frequencies that the tape machine is capable of reproducing. The specification is generally listed as two frequencies (lowest and highest reproducible frequencies) and an error tolerance level of plus or minus so many dB (e.g., 30-18,000 Hz at ±3dB). The wider the range and the smaller the error margin, the better. Analog cassette multitrack and stereo tape decks lack some of the high end frequency response of their digital counterparts. The frequency response of digital recorders is dependent upon their sampling rate. (See Unit 5.). The current generation of digital recording systems can produce a full frequency response range of 20-20,000 Hz with a near flat or even response tolerance. Signal·to·Noise Ratio - The signal-to-noise ratio, or SIN, is a comparison between the level of desired signal and the amount of undesired noise present in a recording. It is often referred to as the noise floor and is measured in decibels; the higher the dB level, the better the signal-to-noise ratio will be (and thus, the lower the noise floor). On a spec sheet, it might be listed as follows: SIN = 75dB. Cassette tape players are particularly prone to tape hiss which results in a poor signal-to-noise ratio (high noise floor).