Artifact: Undesirable sounds around words, such as random, humming noises and metallic sounding breaths. Artifacts can be added to the
original audio from excessive or incorrect noise reduction resulting from technical limitations.
Bandwidth: A measure of a range of frequencies in Hertz (Hz), or musical octaves. See "Q" also.
Brickwall Limiting: A type of hard limiting that causes a full square wave effect. See "Limiting" also.
Clipping: Also called "Digital Clipping", clipping occurs when a digital signal peak reaches or rises above 0dBFS (Decibels Full Scale).
This is often interpreted as an undesirable distorted sound, and should always be avoided. To avoid clipping, reduce the signal's input before the gain stage in which the clipping
Compressor: A dynamics processor that is used to narrow an audio signal's overall, dynamic range by reducing the volume of loud portions, while
amplifying the quiet portions. Adjustable parameters generally include attack, release, threshold, and make-up gain.
Decibel (dB): The standard unit of measurement used to represent sound volume or sound level. In the digital audio world, it is often assumed that when
referring to "dB", it actually refers to decibels relative to full scale (dBFS), where "0dBFS" represents the maximum possible digital level. This means that measurements in the digital audio
realm are generally represented in negative values (-).
Distortion: The audio garble that is heard when an audio waveform has been altered. The distortion, which is undesirable in audiobook narration, usually
occurs when the maximum output of an audio system is exceeded.
Dynamic Range: The ratio of the amplitude between the maximum and minimum sound levels in a recording. This ratio is usually expressed in decibels as
the difference between the loudest possible undistorted level, and the level of the noise floor.
Edited Master: Raw audio (unprocessed) that has gone through the editing/quality control pass (QC pass) stage. This form of audio has
not been processed a.k.a. mastered, but has been edited and corrected (QC pass).
Frequency: The number of times an event repeats itself in a given period of time. Generally, the time period for audio frequencies is one second.
Frequency is measured in cycles per second (Hz), and one Hz equals one cycle per second. One kHz (Kilohertz) is 1,000 cycles per second. The audio frequency range for human hearing is generally
20 Hz to 20,000 Hz. This range covers the fundamental pitch and most overtones of musical instruments.
Headroom: A term related to dynamic range expressed in decibels (dB), as the difference between the typical operating level, and the maximum
operating level in an audio system. The maximum output level of a Digital Audible Workstation (DAW) is 0dB, though many DAWs have additional headroom built into the master fader which allows
sound to be output between +3dBFS and +6dBFS. At Audible Studios, audiobook recordings are limited to a maximum peak of -3dB in order to leave headroom and avoid clipping (distortion caused by
audio peaks exceeding 0dB). This limit allows for 3dB of headroom, leaving room for any surprise peaks that may occur when converting or exporting audiobooks to audible.com.
Interleaved Stereo: A stereo audio file that contains information for the left and right channels as one continuous block of data.
If your files must be presented to listeners in stereo, encoding in this manner is required.
Joint Stereo: A type of stereo MP3 format which cycles through several different kinds of processes to determine the most optimal-sounding
technique for a given frame of audio. This format is prone to errors and glitches. ACX does not accept Joint Stereo files.
Limiter: A type of compressor with a fast attack and release, and a fixed ratio of 20:1 or greater. The dynamic action effectively prevents the audio
signal from rising above the output ceiling setting. See "Brickwall limiting" also.
Mastering: The process of preparing and transferring an edited and mixed audio file to a data storage device; the source from which all copies will be
produced (via methods such as pressing, duplication or replication). Typically, mastering involves dynamic processing, such as limiting, and tonal processing, such as equalization and
Noise Floor: The level of the noise below the audio signal in decibels (dB). Generally considered to be the audible level of background
noise in a recording, where no narration is taking place. See "Room Tone" also.
Phasing: A phenomenon that occurs when two similar audio signals engage one another in an interfering fashion, causing an undesirable ‘sweeping’ effect. This
is most commonly heard when summing a stereo audio file into mono.
Stereo Interleaved: See "Interleaved Stereo"