DV Glossary A - D Conversion Analogue to Digital conversion via a digitiser (see also Quantising). AFM Audio Frequency Modulation, a system for recording sound waves in HiFi quality (>16kHz); standard for Video8/Hi8 format. Aliasing The generation of artefacts after the digitisation of a signal e.g. (1) 'stairstepping' of diagonal lines and (2) 'Moiré' patterns. Temporal aliasing interrupts apparent smooth motion. Alpha Channel The last 8 bits or 4th channel in a 32 bit digital image. Often corresponds to the key channel of the analogue world, used for areas to combine footage. Analogue Represents the intensity of an audio or video signal directly as a value, as opposed to digital. Interpreted as a continuous signal, unlike digital, which is a finite series of samples, Betacam SP, S-VHS, VHS, Betamax, Hi8 and 8mm are all different types of analogue tape formats. Anti-aliasing Minimises the effect of aliasing. A common example is the use of interpolated (or averaged) values to improve stairstepping. Artefact Any spurious image disturbance generated by technical limitations of the system being used. Mosquito noise (or feathering), quilting and motion blocking are three common artefact types. Assembly Editing Editing where clips are simply butted together to form a linear piece. Also refers to a particular form of electronic edit on a tape deck, which replaces all the existing material after the edit point. Aspect Ratio Ratio between the length and width of your screen image. Current analogue broadcast TV mostly uses 4:3, with a widescreen 16:9 currently favoured for HD. Movies can have many aspect ratios, from 5:4 to nearly 3:1. Audio Sampling Like video audio must be digitised, or sampled. Sampling breaks up the sound into discrete frequencies. There are two steps in digitising audio - setting the audio level to avoid distortion and setting the audio resolution or quality. The quality depends on the sampling rate and the bit depth of the audio. The sampling rate is similar to the frame rate in video, it measures the number of frequencies into which the sound is broken. The bit depth measures the number of tones per sample. The higher the rate and the bit depth the better the sound quality. Audio sampled at 11kHz and 8-bit resolution can be thought of as mono sound, and audio sampled at 22kHz and 16-bit resolution (twice the file size) is CD audio stereo quality (usual ranges: 11kHz; 22kHz and 44kHz). 12 bit/32 kHz Audio Sound is recorded on 6 audio sectors (= 1/2 frame, 1 Stereo Channel). 32 kHz sampling frequency allows playback frequency of 16 kHz. The 12-bit mode is mainly used for audio insert and dubbing: additional stereo tracks, e.g. music or voice can be added to the original 6 audio sectors. Total 2 Stereo Channels (both at 16 kHz playback frequency). 16 bit/48 kHz Audio Sound is recorded on all 12 audio sectors (= 1 frame). Three sampling frequencies: 48 kHz, 44.1 kHz and 32 kHz are possible. Maximum sampling frequency 48 kHz gives 24 kHz at playback. That's the quality of DAT with a dynamic range of more than 96 dB. AVI Audio Video Interleave - a digital video format from Microsoft. AVI is now unsupported by Microsoft, as it’s being replaced by Direct Show/Windows Media Technologies.