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. All other trademarks are property of their respective holders. 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. [. . . ] If you want the grounds connected to remove a grounding difficulty, moving the switch to the back position will accomplish this. An LED will light to indicate that you are operating in a non-standard mode. LED GROUND CONNECTED (LED lights) GROUND ISOLATED (Normal) Location of Ground Lift Switch Page 32 AD-1000 Operating Manual Precise Calibration using One LED When you need to make a mix from your analog mixing console, it is necessary to calibrate your AD-1000 to the output of the mixing console. The AD-1000 incorporates a unique feature to enable you to simply match the digital output to within a hair width of your console's meters. The ­12 LED is much more flexible than the labeling would make it appear. When you input an analog signal into the AD-1000, the ­12 LED's threshold becomes variable and coincides with the headroom setting of the digital oscillator. 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. A hotter-sounding CD means not wasting headroom. 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. [. . . ] 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. A single line connection of stereo digital audio must transfer a string of data packages containing left and right audio samples repeated at the sample rate. The single line AES/EBU interconnect divides each package into 64 little pieces of binary bits with 32 for the left sample and 32 for the right. Each chunk of 32 bits is called a subframe. [. . . ]