convertor calibration and input metering with fixed gain preamps

I'm about to start several recording projects after a bit of a hiatus and was hoping to get a better handle on some things this time around. This has led to a couple of questions. In case the reasons for these is unclear, I'll be recording mostly with fixed gain preamps (UA 1108 and Altec 9470) going into linear attenuators - sometimes then into compressors - into my convertors which are Metric Halo LIO8.

The two things I'd like to understand are

1) the Metric Halo software which controls the convertors and provides monitor mixing and other tools before my daw, called MIO Console which is comparable to the software that comes with most convertors, shows input levels as if they were analog, going up to +6. Why is this ? Isn't the metering already past the A to D conversion or am I actually seeing analog dbu levels here ? Does anyone know if there is a way to change this to dbfs so that I have the same 0db at the top that I see in Logic ?

2) is there a place I can specify the calibration point where +6 dbu = -18 DBfs (or whatever it is ) ? Or at least inspect it ?

The thing that is troubling me is that I'm pretty sure my preamps can go up to about +25 dbu clean, but if my monitoring only goes to +6 I can't have any visual indication that I'm at risk of clipping in the preamp before I then attenuate the output. I'm going to be recording bands and doing it all myself, so it is certainly possible I can briefly clip something and not notice it at the time, which of course I'd really like to avoid.

I could pad the inputs or move the attenuators to before the pres in order to make sure this doesn't happen, but then I would not be able to hit the output transformers hard enough to get them to sound their best, which is the whole idea with the rig.

Any advice would be appreciated. By the by, I have a few old posts here under the name teleharmonium which is associated with a dead email account. thanks, Mark

I googled your Interface and found out your maximum input analog input level is +24,5 dBu:
http://mhsecure.com/metric_halo/products/hardware/lio-8.html#tab=3

I'm sure you will find something about your software metering in the manual.

9470 transformers sound just fine at most levels.  They don't need hot drive.  They need 20 dB input pad, or they don't.  They then do or don't need output attenuation depending on the converter max level.  I've probably set up 50 pairs or quads of those for people over the years. 

thanks silent:arts and emrr.

Doug wouldn't the 1108s benefit from some saturation ? I feel like those lovely Reichenbach output transformers are more on the colored side and I think I like them better when I push my luck a bit.

I went through the manual (MIO User Guide) but could not find any options for that display. It's a dual purpose part of that app since it has virtual faders for output from each MIO mixer channel - and for this, I can see why they go to +6 - and also metering in the same space.

I'm getting the feeling I am out of luck for anything in the software. Maybe I need to track down some way to have analog meters that I can temporarily insert after the pre while setting up channels ?

Since you are used to the metering in Logic, why do you want further metering?

silent:arts, the purpose of this metering I am looking for is for setting up a channel before tracking.

Since my preamps have nothing to vary the gain and in fact no controls or metering whatsoever, the key question I am trying to answer on each channel, is do I need to use a pad between the mic and preamp ?

I don't want to use the pads if I don't have to. I've recorded experiments where I used a -20 U pad on one mic and no attenuator after the preamp, and no pad on the other but with 20 db of (balanced, linear) atttenuation on the output (which presumably would give me the same results as putting the pad after the preamp). With two mics of the same type on the same source going into a pair of 1108s  - not that this stuff is exactly matched, but it's as close as I can get -  I definitely liked the sound better with no pad before the pre. I figure this is because I'm hitting the transformers harder. I thought that was widely considered to be a good thing to do if you're looking for a colored, 70s desk kind of sound.

So the goal here is to be able to quickly dial this up in 8 or 16 tracks and be able to check it mid session if I change something.  I would like some way of visually seeing that the loudest signal peaks are going up to around +22 or so - not a lot less, and no more since I would clip the pre with a little more signal.  I just do this by ear and sense of smell if I'm recording myself, but I don't think it will cut it when I am working in bulk.

I can use my meters in Logic to hit my target of an average -18 dbfs level, no problem there. But because that is after my attenuators, it doesn't help with what I am trying to do.

Maybe I should add that it is entirely possible that I am missing something or am somewhat misguided in my approach. But if that is the case I would rather figure it out now, because I'm in the middle of expanding my system out to 16 channels and maybe I would save myself some trouble or find a better way to do it.

I used to record way too hot into my converters, wrongly thinking I was getting better resolution from my bits and lower noise from my analog front end. The mistake I made was disregarding the analog circuitry in the converters, and how good ample headroom sounds both with the converters and my analog front end. Basically I was running everything way too hot into the converter, overloading (IMHO) my mic pres/comps/EQs AND the front end of the converters. Once I configured my converters for -14dbfs = 4dBu, all my sounds improved and became easier to mix. YMMV.

AusTex64, thanks for your reply. I agree with you about not hitting the convertor too hard; but that's not really related to my question. I turn down the signal after the preamps so that I record with an average level of -18 dbfs in Logic.

My question is about how you know where you are in the analog domain when you are above +3 or +4. The analog meters I see max out at this figure, except for one that has both average and peak metering. The peak meter goes up to about +16, which is getting there... but still, I see people talking about clean signal peaks in the realm of +25 in analog gear... lots of high quality preamps are rated for that.  How do they know ? Are they measuring voltage and then extrapolating from there ?

Sounds like you need a peak reading analogue meter where the peak indication corresponds to +22dBu. As you say, VU meters with a peak reading LED calibrated for about +16dBu are available. What you need to do is re-calibrate one of these for +22dBu peaks. So, all you need is to place a 6dB pad in front of it.

Cheers

Ian

Great idea Ian, thanks. I'm embarrassed I didn't think of it.

I think I'll go with 10 db pads since they're easily available and it would make the math a no brainer. I have noticed that while tracking, as when I am setting up my gear before a show, I temporarily lose about 30 IQ points.

ombudsman said:

Great idea Ian, thanks. I'm embarrassed I didn't think of it.

I think I'll go with 10 db pads since they're easily available and it would make the math a no brainer. I have noticed that while tracking, as when I am setting up my gear before a show, I temporarily lose about 30 IQ points.

Click to expand...

It is easy to be so close you cannot see the wood for the trees. Happens to us all.

Cheers

Ian