User manual APOGEE AD-1000

[. . . ] AD-1000 Portable Reference Analog to Digital Conversion System Operating Manual and UV22® License Agreement Revision 2. 1: November 1996 AD-1000 Operating Manual Manual revised for this new edition by: Danny Buchanan, Caryn Perkins, Richard Elen, Johnny Story, Ryan Freeland and Bob Clearmountain. SoftLimit is a Trademark, and UV22 is a Registered Trademark, of Apogee Electronics, Inc. Technology within the AD-1000 including the C768 Low Jitter Clock is covered by one or more patents that are the property of Apogee Electronics Corporation. Registered User Customer Support: For customer support, please call (310) 915-1000 or email support@apogeedigital. com Features and specifications subject to change without notice. © 1996 APOGEE ELECTRONICS CORPORATION 3145 Donald Douglas Loop South Santa Monica California 90405 USA Tel: +1 310/915-1000 Fax: +1 310/391-6262 Email: info@apogeedigital. com Web: http://www. apogeedigital. com/ This manual is copyrighted ©1996 by APOGEE ELECTRONICS CORPORATION, with all rights reserved. [. . . ] This permits precise matching of an analog input to the internal digital oscillator. If the internal digital oscillator is set to the default ­15dBfs position (all three switches in default off) the ­12 LED will remain off until the input level reaches ­15dB (Peak) below full scale digital output. In addition, the LED will blink rapidly to tell you when the signal is within the 0. 05dB of the ­15dB threshold. If you are inputing a calibrated analog sine wave oscillator tone from your console (typically +4dBu for an analog meter zero) you can now adjust the selected gain pots on the AD1000 to make the "­12" LED blink. You have now calibrated the AD-1000 to within ±0. 05dB of the "perfect" digital oscillator. Switching between the analog input (such as +4) and the digital oscillator will show perfect calibration. The calibrated headroom can be varied to best suit your application by changing the digital oscillator headroom. The blinking point for the "­12" LED moves right along with it. The mastering world usually chooses ­12 or ­14dB, tracking tends to be done with ­15 to ­8 dB and the film world tends to play it safe with up to 20dB of headroom. (See diagrams overleaf. ) A hotter-sounding compact disc can be the difference between having a hit or being forgotten. In analog recording we define a nominal operating level and allow enough headroom above to avoid clipping the analog circuitry. This nominal level is usually referred to as `zero' for the 0dB calibration on analog meters. The analog zero usually represents a nominal +4 dBu output level, i. e. when the meter indicates 0 it is really putting out a level of +4 dBu. With digital audio, the precise distortion or clipping point is known. This is the point where we run out of numbers to represent the analog input. This maximum positive (or negative) level is often called an `over' due to the popular labeling of digital meters. The `over' indicators illuminate when a digital maximum is reached, usually for a total of more than 3 samples in a row. NOTE: Some DAT recorders such as the Panasonic 3700 and 3900, indicate `overs' with analog inputs, but do not indicate them with digital inputs such as from the AD-1000. In digital audio we must decide on how much headroom we want above our nominal level (the zero from analog world) before we hit an `over' or digital clip. Any wasted headroom means we are closer to the noise floor than necessary. We require more or less headroom, depending on the material being recorded. Mastering engineers typically choose 12 or 14 dB headroom over their nominal input level because they usually have their dynamics tightly controlled. [. . . ] The transformer input is called differential because the analog audio is carried as the voltage difference between the two wires. The noise signals picked up along the way are called common mode inputs and the ability of the transformer to ignore them is rated as common mode rejection. In professional audio we call differential inputs and outputs balanced and because transformers are bulky and expensive, they are outnumbered in modern equipment by their more economical electronic equivalent: electronically balanced inputs and outputs. As compared to other digital formats which rely on multiple interconnects for clock, left and right data, AES/EBU simplifies the cable connections and uses readily available wire interconnects that are already in use at most professional and semi-professional facilities. [. . . ]