It is a good question and involves a few areas in order to calibrate the system.
The Ref Level
This is the chosen level to which will produce an analog audio output voltage of +4 dBu (1.23 v) at the output terminals as measured by a digital multimeter in AC volts rms mode. Looking at the specs for the VS700R it seems that is -18 dB FS. There are various other digital ref levels such as -12, -14 and -20. I work with a Yamaha digital mixing system that is calibrated for -14 dB producing +4 dBu at my main outs. It can be easily switched over to -20 now being more common.
An alignment tone is created at -18dB (400 Hz or 1KHz) being the level that represents the tops of the sinewave peaks. Track levels, buss and master buss faders should be at 0 dB or
unity setting. No effects plugins or any plugins on tracks or busses. I prefer stereo ref tones being played back on a stereo track. It avoids any pan law effects.
If this is played in your DAW you should see +4 dBu at the main outs of the VS700R. This is measured across the balanced output. With a ref level of -18 it means the output has a maximum output level and that is +22 dBu which is excellent. This is still a clean sinewave output before any clipping is visible.
It is good to have a VU meter plugin inside the DAW and monitoring the Main Output with the output showing 0 dB VU when the alignment tone playback is at -18dB.
Input Levels
Now we can see what range of input levels are required to create this same ref level at the main outs. An oscillator with a digital volt meter measuring its output level is set up and connected into the various inputs of the VS700R. The specs say the input range is from -60dB (0.775 mV) to +4 dbu (1.23v) which is a hefty range.
With the PAD on, minimum gain at the input a +4dBu (1.23 v) input signal should produce the reference level inside the DAW while input monitoring and the correct level at the main output again. With the input gain up to maximum and the Pad off a signal level of -60 dBu (0.775 mv) at the mic inputs will also produce the same ref level inside the DAW and hence at the output again at +4dbu. (1.23v)
Conclusion This applies to any DAW system not just the VS700R. It is simply a matter of identifying what the ref level is going to be. -18 is a very common level but Bob Katz says that -20 dB is also a good ref level and is in line with movie soundtrack levels and specifications. It also means if you are monitoring at 85 dB SPL while the ref level is at -20 dB then you have the potential for the audio system to cleanly go up a full 20 dB to 105 dB SPL and still without any clipping. It also means transients can be 20 dB high creating very clear, fast sounding attack transients in percussion instruments for example.
A lot of commercial music is heavily mastered to average rms levels around -7 and -6dB. While this produces a very high output signal level the dynamic range is also limited to that same amount ie 6 dB which ain't much!
It is a good thing to calibrate your system and beware of the signal levels flowing in and out of your system and how they relate to the ref level inside the DAW system. Many of us have software that is connected to our audio interfaces and some if it is quite complex in terms of signal routing and level changing operations. It is also good to know that signal levels are going in and out of that software.
You can at least start your recording projects at a -20 dB ref level and also at 24 bit for maximum fidelity to begin with anyway. The mix can also still be at this same ref level. Having an un mastered -20 dB ref level mix is good to have. Then after mastering is applied the average rms level will increase accordingly, dynamic range reduced and bit depth/sample rate if applicable also reduced to lower resolutions for distribution.
post edited by Jeff Evans - 2013/01/03 17:43:44