V

VCO

Abbreviation for Voltage Controlled Oscillator. It is an oscillator whose pitch (or frequency) is controlled by an input voltage. In a keyboard, for example, pressing different keys produce different voltages, which then drive the oscillator circuit to produce specific pitches (notes). Modern (digital) keyboards don't work this way anymore, but back in the days of analog synthesizers it was all done with voltage. A lot of the old stuff was one volt per octave. So if it took one volt to go from a low C to the C an octave higher, it took an additional volt to reach the next C up, and so on.

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 (volume) over time.

Video Sync

Also known as Black Burst or House Sync. It is a reference video signal generated by a very stable source (commonly known as a House Sync or Black Burst generator). The signal is used to precisely synchronize equipment to a specific video frame rate. This ensures that multiple machines in a studio are all referenced to one common speed, which is critical for all video editing and production. Some audio equipment is capable of synchronizing to video sync for the purposes of having a common time base in a system and for having the time base be compatible with projects being done for video or film.

Virtual Dolby Digital

Dolby has specifically developed three types of "virtual" surround processing for computers, computer games, and video games. In "virtual" implementations, "phantom" speakers are created, as processing provides perceived sound sources in addition to the actual speaker complement. Virtual Dolby Digital is a computer format implementation of Dolby Digital. For this method, first a Dolby Digital decoder decodes the digital bit stream and 5.1 channel signals are produced. Then, a "phantom" channel is created providing a perceived center channel where none exists, and the two surround channels are processed through an additional DSP circuit and changed to "virtual" surrounds. All channels of information are provided through only two speakers. This system works best for a single listener who is centered between the left and right speakers. In the Virtual Dolby Digital implementation, some computers will decode the digital bit stream via a Dolby Digital decoder with the ability to "downmix" the 5.1 channels into a Dolby Surround encoded stereo signal. These two channels will then go through a two-channel sound card and be processed through an outboard or inboard Dolby Surround Pro Logic decoder to provide four channels of sound -- Left, Center, Right and Surround. The center channel can be switched to "phantom" mode if desired, but four speakers are needed for the left and right front and the two surround speakers at the sides or rear of the listening position.

Virtual Dolby Surround

Similar to Virtual Dolby Digital, Virtual Dolby Surround is another way to use the Dolby Digital bit stream from a DVD-ROM. The first step is for the Dolby Digital decoder to down mix the 5.1 channels into a Dolby Surround encoded two-channel format. The center channel is provided by a "phantom" mode. And the mono surround channel is further processed by additional DSP circuitry and turned into "virtual" surround.

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.

In the domain of MIDI production virtual tracks refer to tracks that exist only in MIDI (as opposed to on a tape machine). A technique that became very popular in the 1980's was to never record MIDI instruments to tape. Instead a MIDI sequencer is synchronized to the tape machines and the MIDI tracks are always "flown in" and mixed in real time as if they are live instruments playing along with the tape. The sequencer stays locked to the tape machine throughout all tracking, overdubbing, and through mixdown. This allows artists to have many more effective or virtual tracks available than what their tape machine would otherwise allow.

.VOC

An audio file type used in computer digital audio. The .VOC file is one of the more commonly found sample sound formats found on PC-compatible computers. It was developed by Creative Labs and supports a packed data format that some programs can unpack prior to importing a file. The .VOC format also supports information for silence, looping, and varying sample rates.

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 vododers 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 amperes) 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.

Voltage-controlled Filter (VCF)

Similar to a VCA, except the control voltage affects a filter circuit. The filter portion can take on a variety of different characteristics (low pass, resonant, etc.), but the general concept is the same. It is a filter circuit whose value is controlled by a voltage applied to it. In keyboards, where VCA's are common, the voltage is often either tied to the note number played (higher notes might open a low pass filter) or to attack velocity (the harder the note is played the more the filter is opened). VCF's are also sometimes found in single ended noise reduction units. These work by opening or closing a high pass filter based on the amplitude of high frequency signals.