Glossary

Audio has its own language. This short glossary provides definitions of some of the audio-specific terms found in this book:

AAC

Advanced Audio Coding, a synonym for the MP4 audio encoding standard [Hack #18].

ADC

An analog-to-digital converter that converts analog signals into digital bits.

AIFF

A lossless audio storage format [Hack #18].

Aliasing

When signals are under-sampled the higher frequencies are aliased, which creates distortion in the lower frequencies. To avoid aliasing, sample the signal at the Nyquist frequency.

Ambience

Background sound material [Hack #64] that augments the foreground audio.

Amplifier

Amplifiers [Hack #14] increase the input audio signal strength.

Analog

Before digital recording there was analog recording, where signals were stored on either tape or vinyl.

Attenuate

A synonym for reduce that is often used to explain the effect of a filter.

Audio Unit (AU)

The plug-in [Hack #51] standard from Apple Computer. It's a part of Apple's Core Audio subsystem in Mac OS X.

Automation

The feature in studio mixing boards [Hack #56] that tracks the position of each control on a channel in real time during recording and playback. In the digital world this is called gain enveloping.

Balanced

A cable is balanced when there are two signal cables and another cable for the shield. A cable is unbalanced when there are two cables and one is used for the shield as well as the signal. Always use balanced cables when you can to reduce noise [Hack #61].

Band-pass filter

A combination of high-pass and lowpass filters [Hack #57] that lets frequencies in the middle pass.

Barsd

A measure of time in a musical score or song [Hack #66]. This is counted in beats. The length of time depends on the beats per measure and the tempo.

Bed

Music that you gain way down and put underneath [Hack #63] a spoken word track.

Bidirectional microphone

A microphone shape [Hack #13] with lobes to the left and the right, but that attenuates sounds to the front and rear. Also known as a figure-eight shape. It's used for radio theatre and single-channel interviews.

Binaural microphones

A matched pair of microphones [Hack #13] set to the sides of the ears, in the ear canal, that are recorded in stereo creating a surround sound effect [Hack #16].

Boomy

When a sound has too much bass.

Bottom

The sound for the end of the show [Hack #63]. The opposite of the top.

BPM

Beats per minute. A music measure of frequency [Hack #66].

Bridge

A long (1530-second) segment of music [Hack #63] that is light in tone and allows listeners to reflect on what they just heard.

Bump

A 4- to 7-second section of music [Hack #63] that has the same volume at the start as it does at the end.

Bumper

A slightly longer version of a bump [Hack #63] (1215 seconds) that starts and ends with the same volume. Also called a buffer.

Buzz

Synonymous with hum [Hack #15].

Cadence

The specific rhythm to a person's speech [Hack #36].

Cardioid microphone

A directional microphone shape [Hack #13] that favors sounds ahead of it while attenuating sounds to the side and to the rear.

Channel gain

The master gain for a single channel [Hack #14]. It applies to the entire signal on that channel.

Chorus

A long delay effect [Hack #58] that gives the impression of multiple singers from a single singer.

Clipping

Clipping occurs in digital audio when the amplitude of a signal exceeds the range of the analog-to-digital converter. All of the signal beyond that range is rendered as the same single clipped value. The result sounds very bad. In older analog systems it was possible to overdrive the system and create a reasonable, even appealing, sound. That is not the case in digital systems.

Codec

The software that encodes and decodes signals [Hack #18] from a file into a raw sound form that can be edited or played.

Cold

A psychoacoustic term that implies that a sound is harsh and unpleasant.

Color

A process that makes slight, but unintended, alterations to a sound.

Compression

Compression filters keep signals within the preferred output range [Hack #56] by attenuating signals that go above a set value. For example, you can set the maximum level at -6 dB and signals above that will be attenuated so that they fall below that value.

Condenser microphone

A microphone [Hack #13] that uses a capacitive diaphragm to measure sound pressure. Thought to produce a more accurate and warmer sound than dynamic microphones. The downside is that they require phantom power. The other type of microphone is a dynamic microphone.

Cutoff point

The point in a high-pass or low-pass filter [Hack #57] above or below which the signal is attenuated.

DAC

A digital-to-analog converter. This converts digital signals back to analog for output in speakers or headphones.

DAW

A Digital Audio Workstation [Hack #61]. For podcasters this means your computer with some editing, mixing, and sound acquisition software.

Decibel (dB)

A measure of sound volume [Hack #56]. The higher the value, the stronger the sound. The lower the value, the softer the sound.

Decode

The act of parsing an audio file and turning it into a raw sound format suitable for editing or playback.

Delay effect

A class of effects that samples the current sound, delays it, and then feeds it back into the signal. These include reverb, echo, chorus, delay, and flanger [Hack #58].

Digital

The opposite of analog. Digital signals are discretely sampled at a set rate into data points of a set bit size.

DirectSound

The Microsoft audio standard. It's also a name applied to Microsoft's plug-ins [Hack #51].

Distortion

Anything that affects a signal. Reverb, chorus, and equalization apply a distortion to the signal [Hack #58].

Dry

When a signal is absolutely free of any effect or filtering [Hack #57]. Dry is on one edge of the spectrum. Wet is the opposite of dry, on the other edge of the spectrum.

DSP

Stands for digital signal processing. In its general form, it's used to describe filtering and effects applied to audio. It can also refer to hardware chips that perform this function.

Ducking

In a two (or more) microphone setup, the sound from the silent microphones can be ducked while the active microphone is brought up. This helps focus the listener's attention to the dominant speaker. It's also used in the political talk show format to tone down callers while allowing the host to talk over them.

Dynamic microphone

A microphone [Hack #13] that uses a voice coil and a diaphragm to measure sound pressure. Contrast this with a condenser microphone, which is less accurate but requires no power.

Dynamic range

The range between the softest sound a system can render and the loudest sound it can render.

Effect

A process that is applied to a signal to distort it by either adding or removing sound [Hack #51]. Examples include equalization, chorus, and reverb.

EFX

Short for effects.

Encode

The act of taking a waveform and converting it to an output format [Hack #18].

Equalizer

An effect applied in the frequency domain [Hack #57] to increase or decrease the amplitude at particular frequencies. Some equalizers have a set number of bands across the frequency spectrum, and others, called parametric equalizers, that allow complete freedom in tuning the frequency response curve.

Field recording

A recording made outside of a controlled studio setting [Hack #69].

Filter

Synonymous with an effect, but usually applied to processes that remove sound elements. Examples are low-pass, band-pass, and high-pass filters.

Frequency response

The curve that represents how a microphone reduces or enhances signals at particular frequencies. Some microphones have a flat frequency response, which is the most accurate. Others boost or attenuate the low or high ends.

FTP

Short for File Transfer Protocol. It is used to copy files from computer to computer. It's often used to transfer MP3 podcast files to a web server account.

FX

Short for effects.

Gain

The amount of boost applied to a signal [Hack #56]. The more gain, the louder the sound. The noise increases by the same amount.

Gain enveloping

The feature in editing programs which allows the gain to be adjusted over the time axis of the signal display [Hack #56].

Headroom

The number of dB between the 0 dB point and the maximum signal that you want in the recording. If the maximum signal you want is 2 dB, there is 2 dB of headroom between that and 0 dB.

Hertz (Hz)

A measure of frequency. Bass signals have a lower frequency in hertz, and higher pitches have a higher frequency. The human voice runs between 50 Hz and 5 kHz with overtones into the 10 kHz range.

High-pass filter

An equalizer set so that high frequencies pass [Hack #57] while attenuating low frequencies.

Hiss

A high-frequency periodic noise [Hack #15]. Sometimes caused by fans or fluorescent lights.

Hum

A low-frequency periodic noise [Hack #15] in the signal. Usually the result of a power bleed into the circuit, or a ground loop, which causes a 50 Hz or 60 Hz hum.

Hypercardioid microphone

A directional microphone [Hack #13] sound shape that favors signals in front much more highly than those to the sides or rear.

In the clear

A sound is considered in the clear when it's at full volume with no other samples layered on top or underneath it. This is most often used to refer to ambient sounds or songs that are either voiced-over when someone is talking over them, or "in the clear" if they are at full volume with nothing else playing.

Kid safe

Considered by the podcaster to be safe for kids to listen to. Usually implies no profanity or intense adult themes.

Kilohertz (kHz)

One thousand hertz.

Lavalier microphone

A small microphone [Hack #13] that is worn on a tie or lapel, or under a shirt.

Low-pass filter

An equalizer set so that low frequencies pass [Hack #57] while attenuating high frequencies.

MAS

The abbreviation for MOTU's Audio System plug-in [Hack #51] format.

Master gain

The gain [Hack #56] applied to the entire signal.

MIDI

Short for Musical Instruments Digital Interface. It's a digital interconnect standard for everything from musical keyboards to control panels to concert lighting.

Mini-disc

A smaller-format compact disc used for recording [Hack #69] and playback. It was supposed to be the next generation CD but never took off in the U.S. outside of audio buffs.

Mixboard

A synonym for mixer [Hack #14].

Mixer

A device that takes several stereo or XLR inputs and mixes them into a single stereo pair [Hack #14]. Often provides gain and filtering controls on a per-input basis.

Monitor speakers

Studio speakers [Hack #61] with a flat response curve that doesn't color the sound in any way on playback.

Mono

A single-channel signal. In stereo systems, a mono signal is rendered equally to the left and right channels.

MP2

A lossless compression standard for audio [Hack #18].

MP3

A lossy compressed format for audio [Hack #18].

MP4

Another lossy compression format for audio [Hack #18]. Also known as AAC.

Muddy

A psychoacoustic term that refers to a sound that lacks definition.

Noise

Unwanted sound [Hack #15] in a signal.

Noise floor

The decibel level of the softest possible signal [Hack #15] a system can render. The better the recording environment and sound system, the lower the noise floor.

Nyquist frequency

The frequency point where all of the recorded frequencies will be digitized without aliasing. This is four times the highest frequency. So, if you want to record sounds up to 10 kHz, you should sample at a minimum of 40 kHz to avoid aliasing.

Off axis

Used to indicate that you are speaking away from the diaphragm of the microphone [Hack #19]. Speaking off axis is one way to reduce plosives.

Off-axis rejection

A measure of the amount of sound recorded from areas out of view of the microphone's diaphragm [Hack #13].

Off the record

When a source is talking but the results are not recorded [Hack #21] and won't be used directly in the resulting story.

Omnidirectional microphone

A microphone sound shape [Hack #13] that weights all sounds around it equally.

OPML

The Outline Processor Markup Language (OPML) is an XML format [Hack #45] used to store hierarchal outline data.

Patch

A generic term that describes connecting a sound source to a sound input.

Parabolic microphone

A highly directional microphone [Hack #13] used at sporting events.

Parametric equalizer

A type of equalizer [Hack #57] that allows complete freedom in defining the frequency response curve of the filter using a number of parameters.

PCM (Pulse Code Modulated)

The storage format [Hack #18] for audio used on CD.

Peak normalization

Changes the amplitude of a signal to maximize its amplitude using the maximum amplitude of the signal [Hack #56]. This normalization technique cannot result in a signal that clips, but it will create uneven volume levels.

Periodic noise

Noise that repeats at a set frequency [Hack #15], such as the hum from a power source or the thrum of an air conditioning unit.

Phantom power

Power supplied through XLR cables to condenser microphones [Hack #14]. Some condenser microphones are self powered with batteries and do not require phantom power. Phantom power is supplied by preamps, amplifiers, and mixers.

Plosive

The sound pop that occurs when people speak the p or b sound directly into the microphone [Hack #19] without a pop stopper.

Plug-in

Software [Hack #51] that fits into a sound recording, editing, or mixing program to provide filters, effects, or virtual instruments.

Podcatcher

RSS aggregation software [Hack #1] that includes support for the enclosure tags in RSS 2.0 feeds.

Pod-safe music

Music that is completely unlicensed, or is licensed under Creative Commons or another license that allows the music to be used in "derivative works."

Proximity effect

The effect when a microphone [Hack #13] gets much louder as you move closer and falls off rapidly as you move away.

Psychoacoustic

A catchall term that applies to signal phenomena, or effects, that aren't easily quantified but can be felt by listeners.

Reverb

Short for reverberation [Hack #58]. The effect of sound hitting surfaces and bouncing back to the recording device. The amount of delay and the effect applied to the return signal gives a room its unique voice.

RMS normalization

Alters the gain of the signal [Hack #56] based on the Root Mean Squared (RMS) average for the signal. This can result in a signal that clips, but it will result in a signal of a consistent volume level.

RTAS

One of the two plug-in standards [Hack #51] for the Pro Tools software. It stands for Real Time Audio Suite. The other Pro Tools plug-in standard is TDM.

RSS

Short for Really Simple Syndication [Hack #37]. It's an XML format that gives a digest of recent entries on a blog. There are three popular versions of the format: 0.91, 1.0, and 2.0. The 2.0 standard supports the enclosure tag, which is what makes podcasting possible.

SFTP

The Secure File Transfer Protocol is the secure version of the older FTP protocol. If you have a choice, always go with SFTP.

Shotgun microphone

A highly directional microphone [Hack #13] used in field interviews and with video.

Sibilance

The hiss for the s sound [Hack #19]. This is removed using a de-esser filter.

Signal

Sound information organized as samples over time. The sampling rate defines how often samples are taken. The sample size, in bits, defines how much data is stored for every sample. A larger sample size can render a larger dynamic range of signal.

Solid-state recorder

A recording device [Hack #69] that stores the signal in solid-state memory. Since there are no moving parts, it cannot be a noise source.

Soundseeing tour

A recorded walking tour [Hack #72] where the speaker describes what he is seeing as he tours around.

SSH

The secure shell protocol allows you to connect to a command-line shell on a remote server machine securely.

Stereo

A two-channel signal that is rendered discretely into the left and right channels of a stereo system.

Stereo pan

The position of a signal in the sound space from left to right. A signal can be all the way on the left, where it will be exclusively in the left speaker, or centered in the middle, where it will apply equally to both speakers. If it's all the way on the right, it will apply exclusively to the right channel. Also, it can be positioned at some point in between.

Stings

A 4- to 7-second musical segment [Hack #63] that starts at one volume and ends at a different volume. Sometimes these have a sustained note at the end that fades out or reverberates.

Stinger

A longer version of a sting [Hack #63] (1530 seconds). Has varied intensity throughout. The ending fades out so that sound can be placed over the top of it.

Studio microphone

Usually a large-diaphragm condenser microphone with a cardioid shape [Hack #13].

Studio recording

A recording made within the controlled environment of the studio.

Supercardioid microphone

A directional microphone shape [Hack #13] that favors signals from the front, and to a lesser degree from the sides, while adding some signal in from the rear.

TDM

The premiere Pro Tools plug-in format [Hack #51]. It stands for Time Division Multiplexing. The other standard for Pro Tools is RTAS.

Telnet

An older protocol to get remote terminal sessions on server machines over the network. It's nowhere near as secure as the more recent SSH standard.

Tempo

The speed of a song [Hack #66]. Usually measured in beats per minute (BPM).

Timbre

The quality of someone's voice.

Tinny

When something has too much treble, it sounds tinny.

Top

The sound for the introduction [Hack #63] to a show.

Unbalanced

The opposite of balanced. A cable has only two lines, where one is shared with the shield and is thus vulnerable to outside interference [Hack #61].

Up-cut

When a person's speech is cut during a rise in a sentence. Sentences tend to fade out. So, a cut when a sentence is rising in volume implies that the person was cut short [Hack #36]. This type of cut is an up-cut because the sound is going up and not down.

Virtual instrument

A musical instrument simulated in software.

VST

A plug-in standard [Hack #51] from Steinberg that works with many audio editing applications.

Walla

The distinctive cheer of a large crowd [Hack #32]. Sometimes used as ambience in sports stories. Each walla has a distinctive sound. The walla of a bar crowd sounds far different from a stadium walla.

Warm

A psychoacoustic term that implies that a sound is rich and deep and is pleasant to listen to.

WAV

The Windows lossless audio file format [Hack #18].

Wet

When an effect is fully applied to a signal [Hack #57], the result is called wet. Dry is at the opposite end of the spectrum from wet.

Work safe

Considered by the podcaster to be safe to listen to at work. Usually implies no profanity or intense adult themes.

XLR

The adapter used with microphones [Hack #13]. XLR cables fit into XLR jacks on the microphone and XLR jacks in the preamp. The jack has three connectors as opposed to two. This means that the cable is balanced, which reduces possible noise introduced by radio frequencies.