Adobe 22011292 User Guide - Page 367

353 Appendix B: Glossary 64-bit Doubles See DBL. 8-bit Signed See SAM. ACM The Microsoft ACM (Audio Compression Manager) is part of all 32-bit versions of Windows. The ACM enables many Windows audio programs to compress and decompress files in a variety of formats, such as DSP Group TrueSpeech and GSM 6.10. Some of these formats come as a standard part of Windows, while others are provided by third parties. ACM formats are sometimes acquired when you install other software. ADPCM ADPCM (Adaptive Differential Pulse Code Modulation) is an audio compression scheme which compresses sound files from 16 bits to 4 bits, yielding a 4:1 compression ratio. There are many varieties of ADPCM, such as the IMA (Interactive Multimedia Association) DVI standard, and versions from Microsoft, Dialogic, etc. A-Law A-Law (or CCITT standard G.711) is an audio compression scheme common in telephony applications. It is a slight variation of the u-Law compression format, and is found in European systems. This encoding format compresses original 16-bit audio down to 8 bits (for a 2:1 compression ratio) with a dynamic range of about 13 bits. Thus, A-law encoded waveforms have a higher s/n ratio than 8-bit PCM, but at the price of a bit more distortion than the original 16-bit audio. The quality is higher than you would get with 4-bit ADPCM formats. Encoding and decoding are rather fast and generally widely supported. Adapter A passive cable, plug, or jack that enables you to connect two audio or video devices together. ActiveMovie See DirectX. ADAT A digital 8-track tape deck manufactured by Alesis Corporation that has been very popular in recording studios. Aliasing Noise that occurs from sampling a high frequency sound at a sample rate that is less than what is required to represent that frequency. A certain sampling rate can represent a frequency equal to half its rate (the Nyquist Frequency). Amiga IFF-8SVX See IFF or SVX. Amplitude Amplitude represents the loudness of a signal. A waveform's amplitude is measured by its distance from the center line (which represents a 0 amplitude value). There are different standards for measuring amplitude, with decibels (dB) being the most common. Analog Recording This is the recording of the ongoing changes of an audio waveform. The analog recording of audio is a continuous curve, as opposed to digital recording, which is based on discrete samples. AIF See AIFF. AIFF This is Apple's standard wave file format. Like Windows WAV, AIFF files support mono or stereo, 16-bit or 8-bit, and a wide range of sample rates. Adobe Audition only supports the PCM encoded portion of the data, even though this format (like Windows WAV) can contain any one of a number of data formats. The AIFF format is a good choice for PC/Macintosh cross-platform compatibility. Extensions are .aif or .snd.