Glossary – Multimedia

ADC Analogue to Digital Converter: converts analogue signals to a stream of digital data
ADPCM Adaptive Differential Pulse Code Modulation: a technique for encoding audio data
AVI Audio Video Interleave: file format consisting of frames of audio interleaved between frames of video
Bit-rate This is the term used for the speed at which the binary digits are delivered to the target system (e.g. a multimedia player). In general terms, the higher the bit-rate, the smoother the playback.

Bit Rate (bits per second) = sampling depth (bits) * sampling frequency (Hz)

Charge Coupled Device, a light detecting sensor
Clipping This is a form of digital distortion which occurs when values in the digital audio data exceed the original sampled range, e.g. when the volume is pushed past the 100% value or some signal processing attempts to achieve a frequency which is out of range. If the volume of a sound signal is beyond the dynamic range then clipping occurs. This can be caused by recording a sound using too high a gain setting, if the sound is louder than expected or if the volume of the sound is edited and increased beyond the dynamic range of the file.
CMOS Complementary Metal Oxide Semiconductor. A type of transistor that can be used as a light sensor
DAC Digital to Analogue Converter: converts from a stream of digital data to an analogue signal
Digital sampling Digital sampling is the process of converting an analogue electrical signal (e.g. the output from a microphone) and converting it into a stream of digital data by measuring the analogue value at regular time intervals.
DSP Digital signal processor: a processor specialised to processing waveform signals
Fade Fade is the term applied to a change in volume. It is used to prevent abrupt starts and finishes of sounds.
GIF Graphics Interchange Format: a format for graphics files, possibly subject to patent restrictions
GPU Graphical processing unit
JPEG Joint Photographic Experts Group: the name used for an image compression format specified by that committee.
LZW Lempel-Ziv-Welch, a data compression technique developed in 1977 by J Ziv and A Lempel, and later refined by Terry Welch.
MP3 The Motion Picture Experts Group’s audio-only specification which delivers high quality musical audio in a highly compressed format. It achieves its high compression rate by combining Huffman encoding with a series of compromises such as recording low level sounds in mono, and removing silences and ‘redundant’ noise.
MPEG Moving Pictures Expert Group: a series of standards for compressing audio and video.
Normalising Normalize is a tool for adjusting the volume of audio files to a standard level. This is useful for things like creating mixed CD’s and mp3 collections, where different recording levels on different albums can cause the volume to vary greatly from song to song. Captured signal may not use the full dynamic range available and the sound does not use the available range of volumes. The signal is clearer if full dynamic range is used, and it makes the sound louder.
PAM Pulse Amplitude Modulation: sampling mechanism for audio signals
PCM Pulse Code Modulation: storage and transmission format for audio data
PNG Portable Network Graphics: a freely available format for graphics files
Rasterisation process of converting from an object oriented format to a discrete bitmap format
RAW ‘Raw’ PCM formats are files of bare audio digitised using Pulse Code Modulation (PCM)
RIFF Resource Interchange File Format: a multimedia data file format. This can define different types of media including AVI & WAV
RLE Run length encoding: a simple compression mechanism working on repeated sequences of the same character
Sampling An analogue sound value measured every nth fraction of a second and stored digitally.
Sampling (or bit) depth The amount of data that is stored per sample.
Sampling Rate The number of sound samples that are taken per second.
Stereo A familiar term to Hi-Fi enthusiasts applied to a pair of audio channels placed one LEFT and one RIGHT of the listener to simulate the human experience of listening with both ears.
Surround sound Refers to a multi-channel audio format designed to give the human listener the experience of aural events happening on all sides. Often Referred to by the number of speakers used ie 7.1 (seven speakers and 1 sub woofer)
SVG Scaleable Vector Graphics file format for vector graphics interchange on WWW
VRAM Video Random Access Memory
WAV This is the RIFF sound format of choice for Windows. A WAV file can be regarded as a ‘bitmapped’ sound file. The ADC conversion in WAV files is done using ADPCM. Uncompressed Wave files are quite large in size so have become less popular.

Glossary of abbreviations:

ADC – Analogue to Digital Converter
API – Applications Program Interface
AVI – Audio Video Interleaved
CCD – Charge Coupled Device
CLUT – Colour Lookup Table
DAC – Digital to Analogue Converter
DSP – Digital Signal Processing
GIF – Graphic Interchange Format
GPU – Graphics Processing Unit
HTML – Hypertext Markup Language
JPEG – Joint Photographic Experts Group
IEEE – Institute of Electronic and Electrical Engineers
LZW – Lempel, Ziv, Welch (compression algorithm)
MIDI – Musical Instrument Digital Interface
MPEG – Motion Picture Expert Group
MP3 – MPEG-1 audio layer – 3
PCM – Pulse Code Modulation
PNG – Portable Network Graphics
RAW – “raw” (unprocessed) data
RGB – Red Green Blue
RIFF – Resource Interchange File Format
RLE – Run-Length Encoding
SVG – Scalable Vector Graphics
USB – Universal Serial Bus
VRML – Virtual Reality Markup Language
WRL – World Description Language
WYSIWYG – What You See Is What You Get
Lists compiled using LTS, Scholar & Vale of Leven Academy notes.

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