July 11, 2016
Audio Production Glossary by Kishore Banan – Part 2
This is a glossary designed to educate any reader who is interested in learning about the various terms and jargons used in the world of Audio Engineering & Music Production. This glossary would be regularly updated with newer words.
TS Cable – TS cable is a single core shielded cable terminated to a TS connector at both ends. TS cable is most popularly used to connect guitars to pedals or the guitar amplifier. TS cable is an unbalanced cable. The unbalanced nature of this cable makes it susceptible to electro magnetic interference. The cable conductors (The core and the shield) behave like antennas to the stray electromagnetic fields. This will manifest as noise in the audio. Do not use long lengths of unbalanced cables as longer cables pick up more noise. TS connector is categorized under the ‘Phone Connector’ family. Regular TS cable uses a ¼ “ Phone connector, ¼” or 6.5 mm refers to the diameter of the connector shaft. T stands for Tip and is connected to the positive signal potential, S stands for Sleeve and is connected to the shield, which is grounded at the equipment side. Colloquially a ¼” TS cable might be referred to as a mono jack-to-jack cable.
DI Box – DI box stands for Direct Injection box. A DI box is used for connecting an unbalanced high impedance output to a balanced low impedance input. In other words DI box allows you to connect a guitar’s output to a microphone preamp or a mixers mic input. Electric Guitars, Basses and Acoustic Guitars with Pickups have a high impedance output provided on a TS connector. In the field of audio, interconnections between various equipment should be configured to provide maximum voltage transfer from output to input. This is possible when output impedance (Source Impedance) is one tenth of the input impedance (Load Impedance). Guitars typically have an output impedance of around 10 kilo Ohms, to transfer the signal correctly, guitar pedals and guitar input of guitar amps have input impedance of around 100 kilo Ohms. Microphone inputs on a preamp or a mixer have low input impedance of around 1000 to 2000 ohms (to match nicely with the typical mic output impedance of around 200 ohms). Trouble happens when a guitars high impedance output (10000 Ohms) is connected directly to a low impedance mic input (2000 Ohms). This is gross impedance mismatch and would result in poor quality sound. DI box addresses this problem by matching input and output impedances. A DI box features a high impedance TS input for connecting the Guitar output and also features a low impedance XLR male mic output which is meant to be connected to the mic input of your mixer. This impedance matching is achieved by using transformer based passive circuitry or Op amp based active circuitry. Active DI boxes can be powered using a battery or using phantom power from the mixer. One last thing to note is that a Di converts unbalanced input on a TS to a balanced output on an XLR. A DI allows you to track a guitar directly without having to mic the cabinet, hence the name Direct Injection. Refer to Radial Engineering website for more information.
Microphone Preamp – A microphone generates very low-level signal. A dynamic mic would provide an output level of around 3 millivolts. A condenser would provide an output level around 15 to 20 millivolts. This amount of signal voltage is classified as mic level. Most equipment in the audio chain does not operate at this level. Mixers, Processors, Recorders etc are designed to operate at a much higher voltage level called as ‘Line Level’. A line level audio signal would have an average voltage of 1.23 volts. As one can see microphone output signal is roughly around 200 times lesser than the operating level of most studio gear. Connecting a mic to a line level system would result in very poor level of audio with excessive noise. Microphone preamp solves this problem by pulling up the mic signal level to line level. A microphone preamp also called mic pre or simply pre provides a low impedance input for the mic signal. This signal is picked up using a solid-state preamp circuit or a vacuum tube based preamp circuit. The user can use the gain knob to dial in the right amount of gain. After pre-amplification the line level signal can be output using a XLR or TRS based line out connection. A typical mic pre would feature an audio level meter and a gain knob, some other utilities such as pad (to drop loud signals), Polarity Reversal (to reverse polarity of the mic signal) and a Phantom Power button to enable phantom power supply to condenser mics. The word ‘Pre Amplification’ is used because ‘amplification’ refers to what is done at the end of the audio chain to drive the monitor speakers.
Mixing Console – Mixing console is a device which allows multiple audio equipment to be connected together. It generally forms the center piece of a studio control room. A mixing console is also called mixing desk, board or simply a mixer. Originally designed in analog, digital mixers have largely become the norm in industries such as live sound, broadcast and post production. A mixing console is divided into two main sections, channel section and the master section, channels are strips of audio circuit laid adjacent to one another, each channel has various input and outputs such as mic in, line in, insert connections, direct out. Channel strips are divided into various sections such ad the input section, bus assignment, eq, dynamics, fader etc. The master section contains all the master controls such as the final mix level, monitor level control etc. Audio from the channels flow to the master section. Mixers are used for a variety of tasks such as multitrack recording to a recorder, creating a foldback mix for the artist, creating a final mix etc. Mixers can be large format such as 72 channel studio board or very compact such as a 6 channel portable mixer for location sound recording. Refer to websites of popular manufacturers such as Soundcraft, Yamaha, SSL etc. for more information.
Reference Monitors – Reference monitors refer to the loudspeakers used by an audio engineer to listen to audio. Reference monitors are high quality loud speakers designed to reproduce sound with a high degree of accuracy. They function as a reference for monitoring the sound quality. Reference monitors are manufactured to provide various features required by the sound engineer. Some of these features are different types of balanced and unbalanced audio input connections in the form of XLR, TRS, TS or RCA connections. Other features could include a power led indicator, volume control, frequency balance controls etc. Reference monitors are available in different sizes, from two way book shelf monitors used for near field monitoring to 3 or 4 way large format monitors used as far fields. Near field refers to a distance of around 3 to 4 feet from the engineer’s position. Bookshelf monitors used for near field monitoring cannot reproduce sound at high levels without distortion, they also exhibit a limited bass response. Far field refers to a distance of around 8 to 12 feet, large format speakers are designed to be installed at such distances. Far field monitors can be mounted on a speaker stand or installed flush into a cavity in the front wall of the studio. Large format far field monitors have high power rating, they can reproduce high levels of sound without distortion and they can reproduce lower bass frequencies with good accuracy. For majority of the time an engineer would use the near field monitors to monitor, occasionally switching to the far fields only to check the mix at high levels and to check lower bass in the mix. Reference monitors are available as active or passive. Active monitors have the power amplifier built into the speaker cabinet, the monitor will feature a power connection and line level audio signal connection. A passive monitor requires an external amplifier, it would have connection terminals such as speakon or binding post meant to connect to a speaker cable. Refer to websites of manufacturers such as Focal Audio, Adam Audio, Yamaha for more information.