The Tech-T Glossary

Part 4

T - U - V - W - X - Y - Z

T

Table Of Contents (TOC): On compact discs, there is an additional track on the inside of the disk that contains information such as the number of tracks on the disc, their location, and their timings. This "table of contents" is what allows a CD player to quickly jump directly to a specific track. Similar methods are employed by DAT machines, MD's, and other types of gear for faster location of tracks.
Talkback: A feature offered on recording consoles, talkback is an in-board intercom system, allowing the engineer and producer in the control room to talk to musicians in the studio. Normally, there is either a built-in microphone for this purpose, or there is a dedicated talkback mic input. This mic/input is routed only to the cue/studio monitor sends, preventing feedback problems with the control room monitors.
Tap Tempo: A function on some MIDI sequencers that allows them to adjust their tempo in real time based on an external input or by "tapping" a button on the sequencer itself. It is used to allow musicians the flexibility of playing along with a sequencer at any desired tempo based on their musical input.
Telecine: A device used for scanning photographic motion-picture images (usually a film format) and transcoding them into video images in one of the standardized video formats. Its most common usage is to prepare videotape transfers from completed film programs. Film scanner is a more general term and telecine is frequently reserved for a scanner that operates only in real-time. In addition to scanning the film images, telecines must reconcile the speed and frame count differences between various film and video formats.
THD (Total Harmonic Distortion): The ratio of the power of the fundamental frequency at the output of a device versus the total power of all the harmonics in the frequency band at the output of the device. Basically, all electronic audio devices introduce some distortion to audio passed through them. The simplest form of this distortion is the addition of harmonics to the outputted signal. THD represents the sum of all the harmonics added by a device as a percentage of the level of the signal being measured. The closer THD is to zero, the more "transparent" a device should sound.; Various devices contribute differing types of harmonic content to a signal, this is part of what can give them their distinctive sounds. For example, tubes add different harmonics than transistors, different circuit designs emphasize different harmonics, etc. When engineers talk about the "sound" of a piece of equipment, this is a part of what they are referring to.
Thermal Recalibration: Thermal recalibration is a process hard drives use to keep themselves operating smoothly as they heat up. Physical tolerances in a hard drive are extremely tight, and as the drive heats up and expands, its performance can suffer. Thermal recalibration allows the drive to correct for any expansion due to heat. Why should you care? Unfortunately, the drive momentarily stops reading or writing data while it is recalibrating - a big problem if you are using the drive for recording audio or video data! Many of the current crop of hard drives are intelligent enough to wait until they are idle before starting thermal recalibration.
3:1 Rule of Microphone Placement: When using two microphones to record a source, normally you will get the best results by placing the second mic three times the distance from the first mic that the first mic is from the source. Confusing? An example: If the first mic is 1 foot from a source, the second mic should be placed 3 feet from the second mic. Using the 3:1 Rule will minimize phase problems created by the time delay between mics. Keep in mind that rules are meant to be broken; you may prefer the sound created by ignoring the 3:1 Rule - experiment and let your ears be your guide!
Threshold: A parameter found on compressors, limiters and noise gates (and a variety of other dynamics-based processors), the threshold setting determines at what level the processor will begin working. For example, on a compressor, when signal level exceeds the threshold setting, it will be compressed; below the threshold signal will be passed unprocessed. On a gate, threshold determines the minimum input level required to cause the gate to open up and pass signal; when input level drops below the threshold, the gate will be closed preventing signal from passing. Carefully setting the threshold allows you to very specifically control when processing is being applied to a signal.
Time Aligned: In speaker cabinets using multiple drivers, the sound produced by each driver can arrive at the listener's ear at different times. (i.e. in a two-way system, the sound from the tweeters arrives before or after the sound from the woofers). This results in degraded transients in the audio. A variety of factors affect this, including crossover, driver and cabinet design. Speakers that are set up to correct for timing problems (whether using electronic delays or physical methods) are said to be "time aligned".
Time Alignment: In a multiple driver loudspeaker system, it is important that the time delay inherent in each driver and its associated crossover network be the same to preserve accurate transient response. In other words, the high frequencies and low frequencies much reach the listener's ear at the same time. A system which meets this criterion is said to be "time aligned." One way to accomplish this is to place the tweeter further away from the listener than the woofer, and this is done in many speaker systems. Another way is to design the crossover network to add a suitable delay to the high frequency signal before it gets to the driver.; The phrase "time alignment" is also sometimes used in reference to adding delay to one or more microphones in a situation where more than one mic is being used on an instrument, and the mics are at different distances from the instrument. A good example of this is orchestral recording where several mics are employed at various distances to accurately capture the sound of the orchestra in the hall. The microphones closer to the orchestra are sometimes delayed to be more in "time" with microphones placed out in the hall.; "Time Alignment" was copyrighted as a trademark by a speaker manufacturer years ago and is no longer widely used as a generic term.
Time Code: A special signal used to record elapsed time on an audio system, time code allows for precise location and synchronization of various pieces of gear. For example, time code can be used to precisely synchronize audio with video during post production. Common formats include SMPTE (Society of Motion Picture and Television Engineers) and MTC (MIDI Time Code).
Transducer: For our purposes, a transducer is an electronic component that transforms one type of energy into another. Some examples: A microphone converts sound into electric current. Likewise, a speaker converts electric current into sound. Other common transducers include magnetic guitar pickups, piezo pickups, phonograph cartridges, and tape heads. One of the main challenges we all face is overcoming the physical limitations transducers put on our ability to reproduce the extremely wide dynamic range of acoustic sounds... deadly enemies of your gear!
Transfer Rate: The amount of data which can be transferred between two points in a given period of time. You will usually see this term used in conjunction with storage media like hard drives, CD-ROMs, DAT backups, etc. Transfer rates become important when trying to determine if a drive can support the demands placed on it by applications like recording and playing digital audio, video, or multimedia files.; Two things to keep in mind with transfer rates:; Transfer rates are CPU dependent. Regardless of how fast your drive is, your computer can only accept data as fast as the CPU can handle it.
Transformer: A transformer is a device consisting of two or more coils of wire wound on a common core of magnetically permeable material. The number of turns in one coil divided by the number of turns in the other is called the turns ratio. An alternating voltage appearing across one coil will be inducted into the other coil multiplied by the turns ratio. Some transformers are designed to operate at 60 Hz and to handle large amounts of current. They are called power transformers, and are found in almost all electronic equipment to change our 110 volt line voltage to one or more voltages more suitable for operating the device. Audio transformers are designed to operate at audible frequencies, and are used to step audio voltages up or down to send signals between devices such as microphones, tape recorders, mixers, and all types of other electronic equipment. Transformers are also sometimes used in audio to provide isolation between two audio circuits. Because the two coils of wire never electrically touch one another a transformer provides a certain amount of isolation that can help prevent ground loops and other problems that can crop up in complex audio systems.
Transient: A non-repeating waveform, usually of much higher level than the surrounding sounds or average level. Good examples of transients include the attack of many percussion instruments, the "pluck" or attack part of a guitar note, consonants in human speech (i.e. "T"), and so on. Due to their higher-than-average level and fleeting nature, transients are difficult to record and reproduce, eating up precious headroom, and often resulting in overload distortion. Careful use of compression can help tame transients and raise average level, although over-compression will result in a dull, squashed, flat sound to the signal.
Transondent: Transondent means transparent to sound passage - similar to transparent in reference to light. Pop filters and speaker grills are two items that should be transondent for best performance.
Tremolo: A cyclical variation in the level (amplitude) of a sound over time. Not to be confused with vibrato, which is a cyclical variation in pitch over time.
Trim: Found on most mixers, trim controls provide the initial level setting for each channel's input gain. In most cases, trim adjusts gain of the microphone preamp, but it may also apply to line level signals. Optimizing this gain stage will make a tremendous difference in the mixers signal to noise ratio and in gain staging later in the signal chain.

U

UART: An acronym standing for Universal asynchronous receiver/transmitter. A UART is an integrated circuit (chip) found in most modern computers that interfaces a microprocessor to a serial I/O port.
Unbalanced: In electronics, a condition where the two legs of the circuit are unbalanced with respect to ground, usually because one leg is kept at ground potential. In other words: An audio signal requires two wires or conductors to function. In an unbalanced situation, one of those conductors is used to carry both signal and ground (shield). Unbalanced circuits tend to be less expensive to construct, but they are much more susceptible to induced noise problems than their balanced counterparts. This is because any induced noise in one conductor is not canceled by similar noise in the other conductor (as in a balanced line) and may be carried with signal into connected equipment. In general, unbalanced lines should be kept as short as possible (certainly under 25-30' maximum) to minimize potential noise problems.
Unidirectional: With reference to microphones, the opposite of omnidirectional. A unidirectional microphone is one which is more sensitive to sound from one direction than from others. The level of "unidirectionality" will vary with the mic's particular polar pattern (i.e. cardioid, hypercardioid, etc.). There is no such thing as a perfectly unidirectional microphone, but the more unidirectional a mic is, the better it is able to reject off-axis sound, producing more isolated signals.
Unity Gain: A device or setting which does not change signal level (amplify or attenuate the signal) is said to be at "unity gain." Many processors are set up for unity gain; that is, they can be plugged into a system without changing its overall levels. In practice, unity gain is often a desired setting for maintaining gain staging, and for optimizing operating levels and signal to noise ratios.
UL: Underwriters' Laboratories, which is a standards and testing agency financed by the insurance industry. The purpose of UL testing is to ensure fire safety of electrical equipment. A device which has been tested and passed by UL will have the familiar round label of certification. UL approval has nothing to do with the audio quality or the functionality of a device. In some states UL approval is a requirement in order to sell equipment that uses electricity.
Ultra SCSI: Ultra SCSI, or FAST-20, is a high-performance SCSI standard which began as an offshoot of the SCSI-2 command set, and is also incorporated in the SCSI-3 parallel command set. Ultra SCSI effectively doubles the maximum transfer rates provided under Fast SCSI-2 to up to 20MB per second on an 8-bit bus and up to 40MB per second on a 16-bit bus (called Ultra Wide). Its terrific performance specifications make Ultra SCSI an attractive data storage and retrieval system for high-end servers and workstations.
Ultra Wide SCSI: Basically Ultra Wide SCSI is a cross between Ultra SCSI and Wide SCSI. Ultra Wide SCSI doubles the bit width of Ultra SCSI from an 8-bit bus to a 16-bit bus, providing much more data throughput (up to 40 MB per second). Ultra Wide SCSI has become the SCSI format of choice for many demanding audio and video hard disk applications.
Ultra2 SCSI: Ultra2 SCSI, also known as FAST-40 is the latest generation of SCSI delivering faster bus speed and longer cable lengths for today's systems and peripherals. Utilizing Low Voltage Differential (LVD) technology, Ultra2 SCSI enables faster data rates and longer cable lengths on the SCSI bus. It doubles the data burst rate of Ultra Wide SCSI to 80 MByte/sec, providing greater system throughput. And it quadruples the maximum cable length of Ultra Wide SCSI to 12 meters, allowing increased flexibility. The benefit of the 80 MB/sec throughput is that data intensive applications, such as CAD/CAM, database access, and 3-D imaging, process more rapidly with Ultra2 SCSI I/O. The greater SCSI bus length translates into greater flexibility in adding external storage and in configuring clustered servers.
Ultra2 Wide SCSI: A wide version of Ultra2 SCSI. Having a 16-bit bus, Ultra2 Wide is one of the fastest SCSI formats currently available and is used in the most demanding audio or video applications.

V

Velocity: In MIDI terms, velocity is how fast a key is moved by the player. There are actually two types: "Attack" velocity (normally referred to simply as "velocity") is how fast the key is struck, while release velocity refers to how fast the player lets go of the key at the end of a note. Velocity is often routed to control the volume of a note, how fast of an attack a note might have, or how bright a sound might be. Release velocity is commonly used to set the amount of time a note hangs or rings on after being released.
Vibrato: A cyclical variation in the pitch of a sound over time. Not to be confused with tremolo, which is a cyclical variation in amplitude over time.
Virtual Track: In the domain of random access digital audio, virtual tracks refer to tracks that are present in a particular session, but are not able to be heard because other tracks are currently using up the available playback resources of the hardware involved. All random access digital audio hardware has limitations to the maximum number of simultaneous tracks that can be heard on playback. In order to hear any virtual tracks they must either be selected as a playable track (which will likely involve deselecting another track that was playing) or some sort of submix operation will have to be done that will allow all tracks to be heard.
Vocoder: An electronic instrument in which the dynamic characteristics of a sound source (usually a voice) are analyzed into a large number of frequency bands, and the resulting information is used to filter another sound source such as a musical instrument. When the dynamic input is a voice the result will be like having the instrument "speak" the notes or chords it is playing. The acronym (how many of you knew vocoder was an acronym?) actually means Voice Operated enCODER and the technology originated at Bell Labs in the late 1940's. The earliest commercial vocoders were developed in Europe by Electronic Music Systems (EMS) and Synton. Over the years Roland and Korg have both had popular models, and now vocoding is having a resurgence as a software algorithm in the sound design community.
Voice Coil: In a dynamic loudspeaker the voice coil is a winding of wire around a cylinder that is attached to the main part of a speaker. The voice coil is inserted into the "gap" created between the magnet and pole piece of a speaker magnet assembly and, when current travels through the wire, generates a magnetic field that causes the speaker to move against the permanent magnet. The alternating current in the voice coil causes alternating magnetic fields to form which interact with the permanent magnet to cause the speaker to move back and forth producing sound.
Voltage: Voltage is an electric charge, or potential, between two points, one being of higher relative voltage than the other is. A 1.5-volt battery has 1.5 volts of differential between the positive and negative end, for example. The unit of voltage is called the "volt," named after Allesandro Volta. Voltage can be thought of metaphorically as a pressure, such as water pressure in plumbing, that is available to initiate action or work. It, however, cannot do any work until a circuit is complete so that current (measured in amperage) can flow.
Voltage-controlled Amplifier (VCA): An amplification circuit whose gain is controlled by an external voltage. VCAs are commonly used in synthesizers to create the volume envelope of sounds. VCAs are also commonly found as the level attenuation devices in compressors, companders and limiters. Some automated mixing consoles also make use of VCAs for controlling signal levels.
VU (Volume Unit) Meter: A VU meter responds in a fashion very similar to how human ears perceive loudness. A true VU meter uses a decibel scale, and is carefully ballistics-controlled (speed-controlled) to conform to specific ANSI-specifications. The reference for power is: +4 dBu sine wave = 0 VU. Originally designed for broadcast and recording, the slow response of VU's was optimized to match the ear's perception of loudness. VU meters give a good indication of average levels, but should not be relied on to display accurate peak and transient levels (Most modern gear with VU meters includes LED indicators as a supplementary peak display). Most inexpensive pieces of gear do not have true VU meters, rather they have decibel meters.

W

Watt: A metric unit of power defined as one Joule per second. The Joule is a unit of energy, so power equates to the rate of energy transfer, or the rate of doing work. Named after James Watt, the developer of the practical steam engine, the watt has become a common term in audio as used to describe the power handling capabilities and/or requirements of speakers, and the power delivery capabilities of amplifiers.
Wavelength: Denoted by the Greek lower-case lambda symbol (g), the distance between one peak or crest of a sine wave and the next corresponding peak or crest. The wavelength of any frequency may be found by dividing the speed of sound (approximately 1130 feet or 340 meters per second at sea level) by the frequency. Thus the wavelength of a 60hz sine wave would be approximately 18.3 feet. Knowing wavelengths of sounds is very important when designing or working with acoustic spaces such as studios, control rooms, and speaker enclosures.
Weighting: Often times when laboratory measurements are taken of audio gear, the literal, "true" figures obtained do not reflect the anomalies introduced by human perception. In these cases, the specs obtained may be mathematically modified, or "weighted" to take into account the way our ears work. A good example is "A-weighting", a curve applied to sound pressure levels to more accurately reflect our loudness perception. Other types of weighting compensate for the ear's frequency response, etc.
White Book: The spec for Video CD, the White Book was developed by JVC, Matsushita, Philips, and Sony. Video CD has never taken off as a major CD format.
White Noise: Random noise with equal energy per frequency is called white noise. It tends to sound very bright and "hissy" due to our ears frequency response curve. (Each ascending octave contains twice as many frequencies as the next lower one, so there is a significant "build up" of energy in the higher octaves.)
Wild Time Code: A phrase used to describe time code that is not resolved to any known reference. It is time code that is just running (or recorded) at whatever rate the time code generator happens to be putting out. This often becomes an issue when someone stripes time code to a video tape without resolving it to the frame rate of the video. The time code will drift relative to video such that it can become impossible to later sync audio material recorded to the working video dub (and its wild time code) to the master video tape.
Word Clock: Digital data is comprised of "bits" which are organized into "words" representing sample values. Word clock is a synchronizing signal based on the sample rate or the speed with which sample words are sent over a digital connection. Word clock is used by the receiving digital device to decipher where in the data stream each sample word ends, as well as whether the word belongs to the right or left channel (in a stereo signal).; When transmitting digital audio signals from one piece of gear to another, it is therefore important that their clocks be synchronized (i.e. the receiving device is made to "slave" its clock to the transmitting device's internal clock, or the whole system is locked to an external house sync signal or master clock), otherwise the sample words in the data stream will not be "lined up" correctly in the receiving device, possibly causing clicks, pops and other audio degradations.
Wow: Wow is a relatively slow variation in the frequency of reproduced sound caused by slow speed variations in records, tape recorders, etc. Pitch fluctuations of one or two per second are classified as wow, while faster variations are called flutter. In spec sheets wow is usually rated, along with flutter, as a percentage where the percentage is the percent of pitch deviation produced by these two phenomenon in the machine. In practice we have found wow and flutter specs to be more of a ballpark or relative measure. Machines can behave very differently depending upon the type of tape used or even environmental factors which can affect tape consistency. This is especially true with cassette type tapes where the tape shell's interaction with the tape is a huge variable. Wow and flutter are almost never an issue in digital recorders because tape speed has no direct bearing on the pitch of the audio playback or recording.
Wrap: In the domain of music equipment, specifically tape recorders, wrap is the angle made by the tape as it approaches and leaves the tape head. Wrap is actually a measure of the distance along the face of the head where tape makes contact. This distance has an effect on the low frequency response of the playback head.

X

XLR: Trademarked name for circular 3-pin connectors developed by Cannon (now owned by ITT). "XLR" was originally nothing more than Cannon's part designation for the connector. In fact, you'll also sometimes see these connectors referred to as "Cannon" connectors. XLR has since evolved into a generic industry term, and many manufacturers now make this style connector. In audio work, XLR connectors are normally used for transmitting balanced mic and line level signals.; Pin 1 of an XLR connector is always ground/shield. The connectors are designed so that pin 1 makes its connection first when inserted in a jack; this ensures that the ground connection is made first, helping prevent pops and thumps in the audio chain.; Either pin 2 or pin 3 may be hot (determined by the gear the connector is plugged into), with the remaining pin being cold. To maintain correct polarity in a signal path, it is important to be aware of which pin is hot or cold on all connections, and wire your cables accordingly.

Y

Yellow Book: Derived from the Red Book, the Yellow Book contains documentation detailing all specs for the CD-ROM format, including track requirements, error correction, and more.

Z

Zenith: The angle the face of a tape recorder head makes with the machine's top plate, or the forward/backward tilt of the head when viewed from the front of the tape machine. If the zenith is not set correctly, the head will not wear evenly, and there will be inconsistent tape to head contact.
Zero Crossing: An analog waveform consists of two alternating voltage polarities (positive to negative to positive...etc.). The point where the polarity changes from positive to negative, or vice versa, is called the zero crossing. When looping a wave or editing two waveforms together, this is the ideal location for the splice as the levels of the two waves are both at zero. This eliminates the possibility of clicks or pops created by mis-matched levels, and makes for a smooth sonic transition.
Zero Reference: In audio, a standard signal level that is defined as the nominal operating level for the audio devices involved. It does not mean zero, or no signal, literally. For example, the zero reference of a device with a balanced +4 dBu input is set so that when a +4 dBu input signal is applied, the meters will show 0 VU, or just be on the edge of going into the red. Often times tape machines are aligned with a Reference Tape that includes tones recorded at the Zero Reference for that machine. Again, the machine would be calibrated so that its meters show zero VU when the Reference Tone is playing. Zero Reference is a concept that has been bent in many different ways over the years. Engineers have adopted all manner of subtle variations on the theme depending upon their personal preferences. And now with the advent of digital recording, a whole new twist has been thrown into things because headroom and nominal recording levels in digital equipment do not look the same as they do in analog equipment. The equivalent of 0 VU on a DAT machine may be -12 (or -14, or -16, or -18) on its dB scale. That means that a +4 dBu input into a DAT will cause a meter deflection of one of these values. When your DAT clips or reaches its "full code" output, the signal coming out of the +4 dBu jacks on the back is probably up somewhere between +24 to +28 dBu. Again, the Zero Reference is down around -12 dB or so on its meters. Calibrating an entire studio or audio chain to agree to a common zero reference is critical to obtaining consistent results and maximizing the signal to noise ratio of the entire system.