User manual APOGEE ROSETTA AD

[. . . ] Rosetta AD 24-bit 2-channel A/D Converter 44. 1/48 kHz version & 44. 1/48/88. 2/96 kHz version Owner's Manual and UV22HR® License Agreement v3. 0 ­ May 2000 Firmware revision 3. 0. 0 ­ inc. Single-Wire Rosetta AD User's Guide Operational instructions written by Joe Raia. "Introduction to Digital Audio" by Julio Alvarez and Richard Elen. SoftLimit and UV22 are Registered Trademarks of Apogee Electronics Corporation. [. . . ] The difference is that these `zeros' are not the same kind of thing. The maximum level on a digital meter is 0dBFS, (a digital "word" of all ones), which is a real, absolute limit, whereas analog signals can go well over `0 dB' on a VU meter without a problem. The Rosetta is set at the factory so that an analog input of `+4dBu' (0 VU on a professional console meter) translates into a digital level of `­16dBFS' (so, to attain 0dBFS, the converter must be fed +20 dBu). It can be adjusted so a +4dBu analog signal translates into a digital level in the range from ­12dBFS (louder) to ­20dBFS (softer). The number of consecutive samples at 0 dBFS required to indicate an `over' on the meters is selectable via DIP switches 3 and 4 on the back panel. See `DIP Switches 1-8' below. METER CLEAR Clears the `OVER' indication (red LEDs) on the L/R level meters. When the `Meter Clear' button is pressed and held for two seconds it will take on its secondary function which is an internal calibration of the 24-Bit Analog to Digital converter. Although the A/D converter is automatically calibrated as part of the power up sequence, you can re-calibrate whenever you want to ­ just be sure to wait five minutes after power has been applied. After five minutes the converter has reached thermal equilibrium, so re-calibration at this time will yield ultimate performance. The converter is also re-calibrated each time the sample rate is changed. You can visually tell that calibration is being performed: the L/R meter displays momentarily, illuminating the middle LEDs of each segment. As the Rosetta recalibrates itself fairly frequently, you will seldom need to do it manually. Note that this calibration is only an internal calibration of the A/D converter chip and has nothing to do with the manual level settings using the L/R level trim below. L/R LEVEL TRIM Adjusts the level sensitivity of the A/D section. As discussed in the METERS description, digital and analog scales are different. The level trim pots allow you to set the Rosetta to an operating level that is convenient for your particular application. Because of the unpredictable dynamic range of live performance, it's often desirable to have plenty of headroom to capture a performance without risking overs. In this case, you may want to set the Rosetta to ­20 or ­18dBFS. The SOFT LIMIT function will also prove to be a useful feature in live recording. In this case, the Rosetta can be adjusted to ­16 to ­12 dBFS to lay down the final mix. Tracking Mixing Mastering In the mastering stage, it's often desirable to get the hottest signal on to tape. The converter does not need as much headroom, so it can be set to ­12dBFS. The chart on the next page shows the relationship between dBu and dBFS for the purposes of setting the levels on the Rosetta. Page 14 Rosetta AD User's Guide The Rear Panel AD INPUT Left and Right Analog inputs. Note: The Rosetta does not contain microphone preamplifiers, so a microphone cannot be connected directly to the AD inputs. [. . . ] (If you're using the one machine we have ever heard of that records at 16-bit, 96 kHz, then I'm afraid we can't help you. ) In most cases you will want to use shorter word-lengths in conjunction with lower sample rates ­ perhaps you'll record at 24/88. 2, but you want to get a CD master at the end of the day. The longer you maintain the maximum word-length, the better it will sound. We are aware of the fact that the DVD-Audio specification allows for different sample rates in the same "family" (44. 1/88. 2/176. 4 kHz or 48/96/192 kHz) for different surround channels ­ say 96 kHz for the front and 48 kHz for the rear ­ and that in theory you can use different word lengths as well or instead, including 88. 2 and 96 kHz at 16 or 20 bits. However, the general view at present is that longer word lengths are worth maintaining, even more than high sample rates. [. . . ]