Converter Calibration

Hey Everyone.

This will apply mainly to guys with analog desks and summers, but where is everyone calibrating their converters to equal +4dBu? I ask because in the last few weeks I've been installing several new desks or converters for clients and it's always a nightmare trying to settle on the best headroom in digital world and also in analog world. This afternoon, in fact, I'm going to look at a client's studio who has two rooms that aren't translating between them.  They like to mix and pre-mix stuff in both but need to be able to swap between the rooms. For them I'm going to see where their main room is set and then cal the secondary room to match.  For HD guys I've sort of settled on -18dBfs  but that can be too hot if they're primarily mixing other people's tracks and have no control over the level that was recorded. On my personal rig, 002 with LE 8, it's not adjustable and is fixed at -12dBfs, which sucks for hitting the desk and staying in the sweet spot between noise and maximum digital levels.

I'm starting to write up a little primer on converter calibration to hopefully be able to explain the reasoning behind it to clients. So far it's just a very stream of consciousness thing, but I'll get it condensed and easily understandable eventually.  I also want to include something about having converters that at least sort of match showing up next to each other on the feeds to the desk.  A few years back I had a client that was complaining he couldn't phase null channels 9-16 on his SSL with the 32 other channels. His normal tech had looked at it for about 2 days before giving up and what it turned out to be was they ran out of their 192s and just threw in something else that was putting out about 2dB hotter of a signal and also about 15ms later. The solution there was to  move it down to the last 8 channels of the desk.

I guess this also applies to studios using hardware inserts and mixing in the box. Need the input level to match the output across all the converters.

Anyways, I am just curious to see if everyone is still in the -18dBfs range or if you've found that most need their outputs a bit quieter and can give up that average/peak headroom.

I think the optimal place would depend on the analog side, 0dBFS is always the same once in digital, the analog clip point doesn't. matching those two levels would be a good start, if it's a single desk with all outputs the same, if a lot of differents analog gear with the same converter are used you may want to choose, maybe de higher to ensure always clip in analog before digital, but you will be loosing a couple of bits in the way, attenuators would be a nice thing to have if you like to hit really hard the analog on certain situations, so maybe -12dBFS and a 10 or 12dB pad would be nice, really strange to see analog go over +24. With some desk working in analog with peaks 10dB before headroom looking for clean and still have the digital side working good, with just a couple of dB for safe. 10dB pads aren't the easier to work with in terms of Z and noise but in line level  shouldn't be a problem.

If you always want the same spot to work just choose one and live with it, the pad may help on hitting hard when you want and work clean in other time.

In the other hand on digital pro gear you always have at more than 100dB of dynamic range to think it quick, in an ideal situation your mic would be recorder with let's say 90dB of dynamic range, so let's give to the digital 10dB of margin knowing nothing would be loosed and forget about the atten, so 18dB is sometimes less than you need, make it 22dB (24dB is too much?) and move on, this way you would be confortable, with no digital clips and in the case a cold mix is on the way you wont be more than the 10 or 12dB that are always unused on digital and only getting the analog noise and you would be already on the 12dB zone that at your 002 seems to be too low.

JS