Glossary

This page gives very brief explanations of technical terms related to digital audio, with some links to Wikipedia for much more comprehensive explanations.

ToDo We need to decide how to anchor all the glossary entries. The easy way is with <H5> headers. It isn't very space-efficient (even in a table, doing which may have accessibility issues) but I think if not in a table it may be less tiring on the eye for actually reading chunks of it? The AllowAnchorTags extension might help, if  it works with <a name> as well as <a href>. See the examples below.

Even after 1.4.0 if needs be, we must also have an Index. And when we do, I think these terms are part of it (because of the overlap between the Index to our pages and the Glossary items). -Gale

General Terms

	Term	Description
	ADC:	Analog to digital converter. This is the part of a sound card active when recording an audio file.
	Algorithm:
	Audacity Project Format (.aup):	The format in which audacity stores audio projects. This consists of a master file with the extension .aup and a large number of small audio files with extension .aff. This structure makes it easier for audacity to move audio around - ideal for cutting and pasting audio in a project.
	Audio CDs:
	Amplitude:
	Bit	A measure of quantity of data. A bit is one binary digit, a 0 or a 1.
	Bit Rate:	The number of computer bits that are conveyed or processed per unit of time. Normally expressed in kilobits per second (kbps).
	CBR:	Constant Bitrate - The rate at which audio in this format uses its data does not vary. Silence uses as much 'space' as audible sound.
	Cepstrum:	Some description here. It's like a logarithm of a Fourier transform. We need a better description [1]
	Clipping:	Distortion to sound that happens when the audio is too loud. When a waveform shows 'flat tops' rather than smooth curves it is usually an indication of clipping.
	Compressed Audio Format:
	Compression:
	Cycle:
	DAC:	Digital to analogue converter. This is the part of a sound card that is active when playing back an audio file.
	Data CDs:
	dB: (decibels)	A logarithmic unit (typically of sound pressure) describing the ratio of that unit to a reference level.
	Dynamic Range:	The difference between the loudest and softest part in an audio recording, the maximum possible being determined by its sample format. For a device, the difference between its maximum possible undistorted signal and its Noise Floor.
	FFT: (Fast Fourier Transform).	A method for performing Fourier transforms (see below) quickly.
	Filter:	A sound effect that lets some frequencies through and suppresses others.
	Fourier Transform:	A method for converting a waveform to a spectrum, and back.
	Frequency:	Audio frequency determines the pitch of a sound. Measured in Hz (see below), higher frequencies have higher pitch.
	Gain:	How much to amplify the sound by.
	Interpolation:	Completing a waveform by an estimate of the values. The values are estimated as being between other known values. To convert a waveform recorded at 22,000 samples per second to one with a value measured 44,000 samples per second interpolation is used.
	Harmonics:	Most sounds are made up of a mix of different frequencies. In musical sounds, the component frequencies are simple multiples of each other, for example 100Hz, 200Hz, 300Hz. These are called harmonics of the lowest frequency sound.
	High Pass Filter:	A filter that lets high frequencies through.
	Hz (Hertz):	Measures a frequency event in number of cycles per second. See Frequency and Sample Rate, both of which are measured in Hz.
	LAME:	A software library that converts audio to mp3 format.
	Linear:
	Logarithmic:
	Lossless:	A format for compressing sound that does not lose any information. The quality is exactly as good as before compression.
	Lossy:	A format for compressing audio such as mp3 that may sacrifice a small amount of quality in order to compress the audio by a greater amount than lossless compression can.
	Low Pass Filter:	A filter that lets low (bass) frequencies through.
	MP3 CDs:
	Noise Floor:
	PCM:	Pulse code modulation. The way audio is converted into numbers and vice versa. Audio waveform is measured at evenly spaced intervals and the amplitude of the waveform noted for each measurement.
	Pitch:
	Red Book:	The most widely used standard for representing audio on CD. Typically CD audio is 44KHz.
	RMS:	Root-mean-square. A method for calculating a numerical value for the average sound level of a waveform.
	Sample Rate:	Measured in Hz like Frequency, this represents the number of digital samples captured per second in order to represent the waveform.
	Sample Format:	Also known as Bit Depth. The number of computer bits present in each audio sample. Determines the dynamic range of the audio.
	Spectrum:	Presentation of a sound in terms of its component frequencies.
	Uncompressed Audio Format:	A format such as .wav in which every sample of sound is represented by a number.
	VBR:	Variable bit rate. A method for compressing audio which does not always use the same number of bits to record the same duration of sound.
	Waveform:
	Wavelength:

Audio File Formats

Unsure if a separate section is a good idea given I think we need entries for lossy/lossless and uncompressed / compressed audio format in the main glossary (e.g. to explain difference between audio signal and audio file compression). A lot depends if we have Audio File Formats as one page as an appendix. Play it by ear but I don't think this table has quite enough detail for each format at the moment, even with a Wikipedia link.- Gale

ToDo As we have now decided not to have separate pages for the different formats (only separate pages for format export options), we need to rethink where these Glossary entries link to - best left until we decide if we have an appendix containing details of "audio file formats" - Gale

	Term	Description
	AIFF
	FLAC:	An Open Source lossless compressed audio format
	MIDI:	A format for audio which represents individual notes. Usually MIDI audio files are captured from a keyboard instrument as pitch and duration of keys pressed, rather than being captured from the sound.
	MP2:	A compressed audio format
	MP3:	A compressed audio format
	Ogg Vorbis:	An Open Source compressed audio format
	WAV:	An uncompressed audio format