ROSETTA 800 Calibration Trimpot Daughterboard

Installation instructions and user’s guide

The Rosetta 800 calibration trimpot daughterboard allows the calibration of the Rosetta’s A/D and D/A levels to a continuously variable value

between +4dBu = -20dBFs and +4dBu = -10 dBFs.

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APOGEE ELECTRONICSROSETTA 800 Calibration Trimpot Daughterboard - User’s Guide

1) Unplug the Rosetta 800, remove the 10 screws located on the top cover, and set them aside where they won’t be lost. Remove the top cover.

2) Locate the analog input and analog output level jumpers as indicated above (figure 1) and remove them.

3) The trimpot daughterboard may be used for both the A/D and D/A sections of the Rosetta 800, depending on the daughterboard’s orientation.

(figure 1)

Installation:

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APOGEE ELECTRONICSROSETTA 800 Calibration Trimpot Daughterboard - User’s Guide

a. Orient one daughterboard so the ANALOG IN legend is facing you. Carefully line up the 8 front jumpers on the daughterboard’s underside with the leftmost jumper pins of each Rosetta 800 analog input channel (figure 2). Carefully press the daughterboard down until it is fully seated on the jumper pins.

Installing daughterboard for ANALOG IN

(figure 2)

Top view of daughterboard as installed for ANALOG IN

Align front jumpers with

leftmost jumper pins

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APOGEE ELECTRONICSROSETTA 800 Calibration Trimpot Daughterboard - User’s Guide

b. Orient the other daughterboard so the ANALOG OUT legend is facing you. Carefully line up the 8 front jumpers on the daughterboard’s underside with the rightmost jumper pins of each Rosetta 800 analog output channel (figure 3). Carefully press the daughterboard down until it is fully seated on the jumper pins.

Installing daughterboard for ANALOG OUT

(figure 3)

Top view of daughterboard as installed for ANALOG OUT

Align front jumpers with

rightmost jumper pins

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APOGEE ELECTRONICSROSETTA 800 Calibration Trimpot Daughterboard - User’s Guide

The goal of converter calibration is to adjust the converter gain to best take advantage of the available dynamic range of the connected analog gear. More specifically, A/D analog gain is ad-justed so that an analog input of a specified standard level (1) results in a digital output at a cho-sen reference level (2); the D/A analog gain is then adjusted so that an input of the chosen digital level (3) results in an analog output at the specified standard level (4), thus preserving unity gain. In other words, what goes in to the converter and through the digital system is identical to what comes out.

For example, with an analog input of +4 dBu the A/D is adjusted for a digital output of –16 dBFs; next, with a digital input of –16 dBFs the D/A is adjusted for an analog output of + 4 dBu.

Calibration of the Rosetta 800

1) There exist several possibilities for generating the required 1 kHz analog tone at either +4 dBu or –10 dBV without an expensive tone genera-tor, including several commercially available Test Tone CDs and computer tone generation applications. Though the tone is generated in the digital domain, the analog output may be easily measured with an inexpensive voltmeter or VU-equipped audio device, as described in (5).

2) While industry standards exist for analog reference levels, the digital reference level, most often somewhere between –20 and 12 dBFs, is cho-sen according to the equipment interfaced and the situation at hand. For example, if one were recording percussion music with the goal of pre-serving every dB of dynamic range, a setting of +4dBu = -18dBFs makes sense, so that the entire dynamic range of the analog gear is employed. If, on the other hand, one were recording a final mix whose dynamic range has been carefully “managed” with level automation and compression, a setting of +4 dBu = -12dBFs makes more sense, to ensure that the full range of digital values up to 0 dBFs is employed.

3) To generate the required 1 kHz digital tone at a chosen reference level, use the aforementioned Test Tone CD and take the digital output of the CD player. Alternatively, many DAW applications include a tone generator that may be routed to the D/A input.

4) Measurement of a 1 kHz analog tone may be easily and accurately accomplished with even the least expensive voltmeter. To verify a level of + 4 dBu from a balanced output, set the voltmeter to measure AC volts, connect pins 2 and 3 of the XLR output to the voltmeter inputs, and adjust the D/A calibration for a reading of 1.23 volts AC. To verify a level of –10 dBV from an unbalanced output, connect the signal “+” to the voltmeter “+” and the signal ground to the voltmeter “–“ and measure for 316 mVolts AC.