Explanation Of Digital Audio; Compression; Tagging; Formats - Numark DDS80 Reference Manual

EXPLANATION OF DIGITAL AUDIO

This section aims to explain a few techie details of digital audio technology. We feel it is important for a DJ to
have an understanding of how this technology can be applied, particularly if it is to be used professionally.
With the right knowledge you will be able to make informed choices and ensure that your performances meet
the highest standard.

COMPRESSION

High quality audio files take up a lot of space, limiting the amount of music that can be stored on media such as a
USB flash drive. To fit more music the files must be compressed, but traditional techniques work poorly with audio,
barely saving any space at all. To solve this problem a new generation of technology has emerged, and it has
taken the music industry by storm!
Modern compressed audio formats such as MP3 and AAC use a technique known as psycho-acoustic
compression to reduce the size of an audio file. Not all data in an audio track is significant to the human ear, so it's
possible to discard certain parts of the wave or combine other parts without significantly changing our perception
of the sound. Furthermore, some parts of a wave mask other parts so those too can be discarded. What's left can
then be represented in a very efficient format, resulting in a file many times smaller than the original while barely
alterating our perception of the audio. Because some of the original information has been lost these formats are
sometimes known as "lossy". By choosing how aggressively to apply the compression we can trade off between
the size of the file and the quality of the audio.

TAGGING

Apart from audio data most formats also contain information about the track, known as tags. Such tags as track
title, artist name, album title, BPM (Beats Per Minute) and Genre are often included. The best audio applications
offer a feature to automatically fill in these tags when converting your CDs, and some can even identify tracks
which have been recorded from vinyl or other sources. Otherwise, you can type in and edit tags manually.
We strongly recommend that you take the time to ensure your music collection is well tagged. While this could
involve significant effort for a large poorly tagged collection, it will pay back many times over when you perform.
DDS makes extensive use of tags to organise your music collection and provides powerful methods to find tracks
quickly and effectively.

FORMATS

DDS supports three of the most popular audio formats - two compressed (lossy) and one non-compressed
(lossless).
MP3
This is the format that started the revolution. Invented in the early 90s for the broadcast industry, it
exploded into the music industry several years later with the invention of the portable MP3 player. Now it
has become almost a generic term for digital music, although MP3 is just one of many compressed music
formats in use today.
MP3 in particular can draw criticism over sound quality. In its early years storage was expensive so
tracks were often compressed heavily, degrading sound quality. Now, with large flash memory keys and
hard disks more affordable than ever, there's no reason to over compress, especially for professional
use. It has been demonstrated that with a bitrate of 256K bits per second (bps) the vast majority of
listeners cannot distinguish from an uncompressed original. This gives a file size approximately 20% of
an uncompressed recording.
A popular option offered by many encoders is Variable Bit Rate (VBR). The bitrate will change throughout
the track so that simple parts take less space while more complex parts take more to ensure high quality.
Most encoding programs allow you to select an "average bitrate" for VBR - choosing 192K, for example,
will lead to a file about the same size as a Constant Bit Rate (CBR) 192K file, but the quality will be better
overall.
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