Symphony I/Oʼs A/D and D/A converters may be calibrated to operate at optimum levels with a wide variety of analog gear.
The calibration process is performed in the following three steps:
- Choose Analog Input and Output Levels
- Choose Digital Input and Output Ref (Reference) Levels
- Adjust Input and Output Trims.
Step 1 - Choose the Analog Levels
In Maestro's Intput tab, set Analog Level to match the nominal operating level of connected analog equipment. Consult the operating instructions of the equipment to determine its nominal operating level. The following settings are available:
- +4 dBu - Choose this setting when connecting to professional audio gear that operates at a nominal level of +4 dBu. As a general rule, high-end mic preamps, professional mixing consoles and tape machines operate at +4 dBu nominal level.
- -10 dBV - Choose this setting when connecting to semi-pro or consumer gear such as home stereos and “project” studio equipment.
- Variable - Choose this setting when a precise nominal level setting isnʼt necessary. For example, the operating level of electronic instruments may greatly vary from model to model; by choosing Variable, itʼs easy to obtain a satisfactory input level without a lot of fuss.
When connecting Symphony I/Oʼs Inputs and outputs to the same device (for example, a mixing console), itʼs best to set the analog output level (in Maestroʼs Output tab window) to the same setting as the input level, to preserve unity gain.
Step 2 -Choose the Digital Reference levels
The Digital Reference level determines the amount of headroom before digital overs occur, and is set according to user preference.
As a general rule, the more unpredictable the audio source being recorded, the lower the Digital Reference should be set in order to maximize headroom.
For example, when recording musical content with unpredictable peaks, set Digital Reference to -18 or -20 dBFs. When recording an automated mix, where dynamic range is both carefully managed and peaks are predictable, a higher Digital Reference (around -14 to -12 dBFs) may be preferable.
Again, itʼs best to set the Digital Output Reference level at the same setting as the Digital Input Reference level, to preserve unity gain through the system.
Step 3 - Adjust Trims
When interfacing even the highest quality analog gear, slight level adjustments are necessary to ensure that each channel’s actual gain equals the theoretical gain based on the analog and digital levels selected. Follow these steps to trim each channel:
1. Click Show Trims on the Input and Output tabs to display trim faders for each analog channel.
2. Connect a 1kHz sine wave to an A/D channel at a level equal to the selected analog reference (for example, +4 dBu).
3. Adjust the channel’s Input trim fader until the actual digital level, as displayed in the Meter Level Readout, is equal to the selected digital reference. For example, if Digital Ref is set to -16dBfs, it's likely that the actual level detected in Maestro will equal something like -16.2 dBfs. Adjust the Trim fader until the detected level equals -16.
4. To calibrate the D/A, route a 1kHz sine to a D/A channel at a level equal to the selected digital reference. Most digital audio workstations offer a Test Generator function to generate a sine wave at a specified digital level.
5. Adjust the channel’s Output trim fader until the signal reads +4dBu (or the selected Output analog reference) using an external meter. If using a standard volt-ohmmeter, set it to read AC Volts, and adjust the trim until the external meter reads a voltage of 1.228 V. Note that on the Output tab, the Meter Level Readout ispre-Trim, so that adjustments to the Trim fader aren't reflected in the level displayed.
6. Note that when Output Digital Ref is set to -20dBfs, only a negative Trim value is possible (0dB to -2 dB).