lifted from Sonic Sense website:
Microphone Pre-amp calibration with decks and analog-to-digital converters
In response to repeated questions regarding calibrating of a/d converters with pre-amps, we are now offering the following detailed calibration process.
Having described this process repeatedly to numerous pre-amp and a/d converter users, we were fortunate enough to have Ryan McKinney offer to type the following information as I explained it. This should serve as a guide but we still welcome you to call us as you put together your system and need assistance optimizing the gain settings.
As we have seen many people fumbling with flashlights in their teeth while trying to hold a flashlight and screw driver on their knees at a show, the following steps should enable a/d converter users to set-up their converters one time at home and simply rely on the pre-amp for further adjustment.
To calibrate the Graham Patten ADC-20 or the Apogee A/D 1000, the calibration pots will prove to be the most useful. In the case of the A/D 1000, this also prevents the potential for the knobs to get bumped at a show since the calibration pots are recessed.
Steps:
Connect all of your gear.
Place mics in front of one loudspeaker.
Set the stereo to a non-dynamic source such as fm static or white noise,
DO NOT use a cd or talk show or any source with fluctuating volume.
Turn Pre-amp to its maximum setting on both gain levels and trim levels.
Turn up radio volume until +16 dbu on the preamp just starts to illuminate. (on the V2 this is when the red lights first come on).
If using a Lunatec V2, adjust AD converter until the meters on the DAT deck peak at -6 to -8db.
(the small Sony Recorder most likely will have to set at 6, as there is no "-8db" marking on the display meter).
If using a Sound Devices MP-2, adjust AD converter until the meters on the DAT are peaking at -2db when MP-2 +16db blinks.
Adjust the L and R channels until they are balanced.
A couple of unit specific notes:
Note that the ADC has 20 turn pots, so you may have to turn them quite a bit to get the levels where you want them.
Caution: when turning the adc20 up, if you hear clicks, stop, it means you have exceeded the threshold of the unit.
As we know that the V2 red light illuminates at +16dbu but that it does not clip until +26, this gives us a 10db buffer zone. If your +16 creates a -6db on your meter, then you can safely assume that even when the V2 is flashing a lot of red, but only putting a -2 or -1 on the tape, you are only 4 or 5 db into "the red zone." As a result, you will know that you are not overdriving/ clipping the pre-amp. Remember, however, that the V2 trim controls only affect the output of the unit and that the front panel meter are responding to the input gain. Thus, for each db of trim that you introduce, you are compromising the overall headroom (i.e. the 10db that you would typically have if the trim pots were all the way open to zero).
The MP-2 will clip between +20-22dbu so this process leaves roughly 4db of headroom while obtaining optimal levels on the recorder
The benefit of calibrating your pre-amp with your deck or a/d converter is multifold:
You will know that you are not overdriving/clipping the pre-amp.
You will know how far you are into the pre-amp's margin/headroom.
You will not overdrive the pre-amp and assuming that you do NOT go over zero on your DAT meters, you will not have distortion/clipping on your tapes
Topic: V2 calibration? (Read 6375 times)