Apple MA261Z/A User Manual - Page 570

Amplifiers and Signal Levels Audio speakers require signals with higher voltage than consumer and professional equipment can provide directly. Speakers require speaker level audio signals, while audio devices such as tape recorders and audio mixers usually provide line level signals. An audio amplifier boosts line level signals to speaker levels to properly drive speakers. Wide gauge speaker cables that can handle the higher electrical strength of speaker levels are used to connect the amplifier to speakers. For more information about audio signal levels, see "Microphone, Instrument, and Line Level" on page 574. Self-Powered Versus Passive Speakers Speakers powered by an external amplifier are called passive speakers. When you use separate amplifiers and passive speakers, complex factors such as impedance matching and cable length affect the overall frequency response and quality of your audio. Instead of using a separate amplifier and speakers, a simpler option is to use selfpowered speakers (speakers with built-in amplifiers). These have become increasingly popular, especially for studio monitoring and video editing. Self-powered speakers deliver more consistent performance because both components are designed to work together and are housed in a single enclosure. For video editing systems, self-powered speakers are a good, easy-to-use solution. Self-powered speakers accept line level inputs, so it's fairly easy to connect them to your audio interface. Matching Your Mixing and Screening Environments It's critical that you monitor your mix in an environment that closely matches the final viewing environment. A movie destined for a theater should be mixed on an audio system that matches the theater sound system. Likewise, a movie destined for DVD release for home viewing should be mixed on a system that resembles a home viewing environment. Setting Up a Proper Audio Monitoring Environment Room shape and material are just as important as the quality of the speakers themselves. Every surface in a room potentially reflects sound, and these reflections mix together with the sound originating from the speakers. Rooms with parallel walls can create standing waves, which are mostly low-frequency sound waves that reinforce and cancel each other as they bounce back and forth. Standing waves cause some frequencies to be emphasized or attenuated more than others, depending on your listening position. When you mix in a room that creates standing waves, you may adjust certain frequencies more than necessary. However, you may not notice until you play back your audio in a different listening environment, in which those frequencies may sound overbearing or nonexistent. 570 Part VIII Audio Mixing