Adobe 65009626 User Guide - Page 97

USING SOUNDBOOTH CS4 93 Digital audio glossary Nyquist frequency A frequency equal to half the current sample rate, which determines the highest reproducible audio frequency for that rate. For example, audio CDs use a sample rate of 44,100 Hz because the resulting Nyquist frequency is 22,050 Hz-just above the limit of human hearing, 20,000 Hz. For the best audio quality, record and edit at higher sample rates and then convert down if needed. P PCM (pulse code modulation) PCM is the standard method used to digitally encode audio and is the basic, uncompressed data format used in file formats such as WAV and AIFF. phase The position of a sound wave relative to other sound waves. As a sound wave travels through the air, it compresses and expands air molecules in peaks and troughs, much like an ocean wave. In the Soundbooth waveform display, peaks appear above the center line, troughs appear below. If two channels of a stereo waveform are exactly opposite in phase, they will cancel each other out. More common, however, are slightly out-of-phase waves, which have misaligned peaks and troughs, resulting in duller sound. (See also "Waveform measurements" on page 6.) processes Intensive functions that require dedicated computer power, briefly preventing you from editing audio. Processes permanently change audio data. (Compare with "real time" on page 93.) Q quantization A process that occurs when an analog waveform is converted to digital data and becomes a series of samples. Quantization noise is introduced as some samples are shifted to quantization levels allowed by the current bit depth. This noise is highest at low bit depths, where it can particularly affect low-amplitude sounds. R RCA cable Sometimes called a phono cable, RCA cables have RCA plugs or jacks at either end and are normally used to connect stereo system components, such as receivers, CD players, and cassette decks. real time Describes functions that immediately respond to user input. Real time functions leave audio data intact, so you can readjust settings in the future. (Compare with "processes" on page 93.) In Soundbooth, real time functions include effects and mixing controls. resample To convert a sound file to a different sample rate and bit depth. In Soundbooth, you resample files by using the Save As command. (See "Save entire files or selected ranges" on page 72.) reverb The reverberant sound produced by an acoustic space, such as a room or concert hall. Reverb consists of dense, discrete echoes that arrive at the ear so rapidly that the ear can't separate them. RMS (Root-mean-square) A mathematical formula used to determine the average amplitude of an audio selection. RMS amplitude reflects perceived loudness better than peak amplitude. S sample A digital snapshot of an audio waveform at a particular point in time. In digital audio, a series of numeric samples reproduces an entire waveform, with higher sample rates producing increased frequency response. (Note that musical samplers use the term sample to describe a digital recording, rather than a digital snapshot.) sample rate The number of samples per second. Higher sample rates provide a greater frequency range but increase file size. For details, see "Understanding sample rate" on page 8. signal-to-noise ratio Describes the difference between the highest signal level before distortion and the average level of the noise floor. In most analog systems, such as microphone preamps, the signal-to-noise ratio is around 92 dB. Updated 15 July 2009