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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. We're starting to see similar methods 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.

Tape Saturation

See Saturation

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.

TDIF

Generally pronounced TEE'-dif, it is an acronym for Tascam Digital InterFace. This is the protocol Tascam developed to use in their MDM and digital mixing products for doing digital transfers of audio. TDIF connections are made via a 25-pin d_Sub connector and data is carried on shielded cable. The TDIF standard is currently one of two major formats (the other being ADAT optical) widely used in pro and semi-pro MDM related products for digital transfer of more than two tracks of audio simultaneously using only one cable.

Telecine

A device used for scanning photographic motion-picture images 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.

Telescoping Shield

Refers to a shield configuration in shielded balanced cables. When the cable shield is connected at one end of a cable, but left "floating" or unconnected at the other it is said to be telescoping. A cable's shield does not necessarily have to be connected to ground at both ends in order to provide effective shielding so they are often telescoped in studio wiring to reduce the likelihood of ground loop problems. Which end of a cable's shield gets left floating (the source end or the destination end) is a subject that is debated in the tweaky circles of studio designers, but most people lift it at the source.

Temporary Threshold Shift

TTS for short, this is an upward shift in the threshold of human hearing. It is usually caused by being subjected to a loud sound. The human auditory mechanism is remarkably tolerant of abuse, and it has several ways of protecting itself from damage when exposed to very loud sounds. One of these is to reduce its sensitivity, causing the hearing threshold to shift upward. As the name implies it is a temporary condition, but continual exposure to loud sound will cause it to become permanent. This is known as permanent hearing loss. You only get one set of ears for life, so take care of them. Make it your New Year's resolution.

Terminal Strip (a.k.a. barrier strip)

A series of connections, usually screw terminals, arranged in a line to permanently connect multiple audio lines to such devices as recording equipment, mixers, or outboard gear. Back in the '70's much of the high end recording equipment only had terminal strips on the back for connection. Since this equipment was primarily used in pseudo-permanent professional facilities it was considered the most cost effective and reliable way of connecting things. Nowadays most pro equipment is fitted with some combination of 1/4" (TS or TRS), XLR (see WFTD archive XLR) and possibly still terminal strip connections. Equipment sold primarily for use in permanent installations (contracting) such as stadium or theater sound is still frequently equipped with terminal strips only.

Terminator / Termination

Besides being a popular movie and a WWF wrestling star, a terminator is a device used when interconnecting equipment that has high frequency information (like video or digital data) passing between it, though termination can also be an issue at low (audio) frequencies. If you've ever heard an echo on a long distance phone conversation it was most likely a termination problem. In practice a terminator is often just a simple resistor or set of resistors placed at each end of a transmission line. Termination is required on video signals, SCSI chains, and other types of data transmissions. Its function is to match the impedance of the source and the load (destination), which, among other things, prevents a phenomenon known as reflections from occurring on the line. Reflections disrupt the purity of the signal in a variety of ways and can cause data drop outs and generally poor performance. A transmission line is said to be terminated if it is connected to an impedance equal to its characteristic impedance. Under these conditions a signal will "enter" the terminating impedance as if it were an infinitely long extension of the line, and no energy will be reflected.

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 (all other things being equal, which they never are...).

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.

Theremin

An unusual electronic instrument developed in 1919 by Leon Theremin. The Theremin had two antennas and was played by moving one's hand closer to and further from them. One antenna controlled the volume and the other controlled the pitch. A skilled Theremin player could produce a wide variety of interesting sounds and musical phrases. The sound of a Theremin is a sort of eerie whining type of sound and was used for "effect" in some popular music of the '60's and '70's (for a good example check out the beginning of Good Vibrations by The Beach Boys). After modern synthesizers became commonplace the Theremin faded into relative obscurity. Today there are still some die hard Theremin fans out there with clubs and users groups. Also, Bob Moog (a major developer of the modern synthesizer) is now building and selling new hand made units though his company, Big Briar.

Thermal Noise

Also called Johnson noise, is the random white noise found in any conductor or electronic device. It is produced by the thermal agitation of the charges in an electric conductor and is proportional to the absolute temperature of the conductor. It manifests itself in the input circuits of audio equipment such as microphone pre amps, where the signal levels are low. The thermal noise level is the limiting minimum noise any circuit can attain at a given temperature. Modern high-quality microphone pre amps, under proper conditions, have noise specifications that come very close to this theoretical limit.

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

Yesterday we discussed the 2:1 Rule of Ambience. Today let's go one better with the 3:1 Rule of Mic 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.

This rule originated when engineers were micing multiple sources in the same vicinity. The same principle applies. If you are recording two different sources of sound, their respective microphones should be at least three times further apart than they are close to their respective sources. 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.

Timbre

Pronounced "tamber," it is the subjective quality or tone color of a sound; the essential quality of a sound that makes it what it is. An oboe has a different timbre than a tuba, for example. Two oboes may have a slightly different timbre from one another. They sound different. Timbre is made up of all of the qualities of a sound: transient attack, harmonic content, envelope, overtone structure, and more.

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 (see WFTD archive 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

Literally, a code containing or relating to timing. Since the early days of audio it has been necessary to synchronize (see WFTD archive synchronization) audio tracks to motion picture. Later, with the advent of video, MIDI, sequencing, and other technologies the necessity for synchronization of these various formats has become a core concern for production studios and engineers. Almost all time codes are used by recording the "code" on the media of two (or more) machines and then, when the machines are operating, the codes are compared by a synchronizing device which can control slave machines to keep them in sync with the master machine. All sorts of different kinds of timing codes have been used over the years to achieve this, but the current standard for most synchronization needs is SMPTE time code which is comprised of an eight-digit number, based on the 24-hour clock, that identifies a specific frame in a tape. Due to this near standardization, and the ubiquitous nature of SMPTE as a time code format, the words "time code" and the acronym "SMPTE" are used almost interchangeably. There are other time code formats, many of which are based on SMPTE, that we will discuss in the future.

Time Out

1. What Duke coach, Mike Krzyzewski, ran out of in the late minutes of his recent Final Four battle against the mighty, and victorious, KENTUCKY WILDCATS (yes, your inSync editor is from KY).

2. A colloquialism often used in electronics to describe the termination of a particular type of wait state for a device. For example: If you press record and pause on most DAT machines you have put the machine in a state of waiting for a play or stop command. Most DAT recorders will default back to the stopped state if they do not receive further commands within a few minutes. This is known as "timing out."

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 (remember those?) and tape heads. One of the main challenges we all face (whether we know it or not) 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:

1. A drive's transfer rate may be different for reading and writing data.
2. 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 (see WFTD archive "Hertz") 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.

Transient Response

Subjectively, the ability to generate sounds that start and stop quickly, with a great sense of speed. Objectively, a very slippery word which can apply to upper limit bandwidth, phase response, group delays, impulse response, decay time, etc. Often the phrase is used with intent to describe a device's ability to reproduce transient information accurately. Transients are difficult to record and reproduce, yet are critical bits of information that we use as cues to recognize sounds.

Transondent

This one is sure to impress if casually thrown out at a gathering of audiocentric individuals! 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.

Transwave

A specific type of wavetable synthesis used in Ensoniq instruments. It's comprised of a wavetable of sound data with a number of loops, rather than just one. These are generally called frames. Each frame has a slightly different harmonic structure, and they're arranged sequentially so that the timbres progress naturally from one end to the other. This produces a sound that will change characteristics over time as it plays through the wavetable. Additionally it is possible to have playback begin and/or end at specific points in the wavetable, and this can further be manipulated by continuous controllers.

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.

TRS

Abbreviation for Tip Ring Sleeve. This is the descriptively accurate term used to describe 1/4" (or 1/8") balanced connectors. A TRS plug can be found at the end of most headphone cords if you want to know what one looks like. They look like a standard 1/4" plug with an extra section in them. The three sections of the shaft are called the Tip, Ring, and Sleeve (a "standard" 1/4" connector just has a tip and sleeve). TRS connectors are used wherever it is desired to have two conductors plus a ground (shield) in one plug. Common uses are as a way to connect balanced equipment (where the TRS plug has a positive, negative, and ground connection), or stereo unbalanced equipment (left and right are on the Tip and Ring, with a common ground) like headphones, or as an insert for your mixer or other processor (Tip or Ring is the send with the other being used as the return and again ground is common).

True Stereo

A phrase used to describe the architecture of modern effect units that can truly process a stereo input as two discrete channels. When early digital reverbs and multi-effect processors hit the market they had processors in them that could generate a stereo output (often reverb) from a mono input. In fact, that's the only way they worked. The processors inside only had one input, and the output was a synthesized stereo signal. Some of these devices later showed up with stereo inputs to the unit, but those signals were summed to mono before entering the processor itself. If you were connecting the unit in line with a stereo signal the dual inputs provided a way to keep the dry (unaffected) portion of your signal in stereo. As the cost of processing technology dropped manufacturers were able to include dual processors in equipment. One of these processors could be dedicated to each input allowing two different effects to be used at once (one on each input). These processors could often have their control signals ganged together so they would act as one true stereo processor. Nowadays there are processors on the market that can accept two signals directly and process them.

2:1 Rule of Ambience

To capture an equal amount of room ambience, a cardioid microphone must be placed twice as far from a source as an omnidirectional pattern microphone. Keep this in mind the next time you are trying to capture some of a room's natural sound when recording!