gain on FWx playback

[smokeydan]

I have several session which I've recorded onto a PTHD rig using the HDX card in the FOH rack- but now that the FWx option is capable of 32 channels of I/O I want to start using it for "virtual soundcheck" - but I want to know how the level from the FWx will relate to the level if I was playing back using the proper "virtual soundcheck" feature with the HDx card.

I've read through the live recording guide and it seems a little vague- all I can find is "Channel input gain from Pro Tools will always be 3–6 db lower than your Stage inputs input gain, depending on recording levels. You may have to adjust the input gains for the Pro Tools inputs to approximate the levels of the live Stage inputs."

I would have thought it would be possible to put a specific dB value on it so that you could set gains on the FWx assignable inputs to exactly match the level of the live inputs from the stagerack- does anyone have experience with this?

thanks on advance

D

[smokeydan]

I got my question answered- In case anyone else needs to know or didn't realise (as was pointed out, the info is all there in the signal flow diagrams in the manual…..)

the pick off point for FWx recording is the same as for HWx recording- ie post analog gain (obviously) but pre the digital gain stage. The return point for FWx playback is also the same- so there will be an adjustment required on the digital gain for most channels to get accurate input level- I believe it will be between 0 and 2.9dB as the analog gain seems to go up in 3 dB steps and is fine tuned with the digital stage. I'm not sure why the manual says 3-6dB

It follows that you should be able to load your session into the standalone software, tell it you're connected to an HDx card, select virtual soundcheck mode and read off the required digital gain adjustment per channel from that.

10dB gain in live input mode (with or without pad) = 0.2dB digital gain in HDx or FWx return
10.8db = 1.0dB
12.7dB=2.9dB
12.8dB=0dB etc

[digidesigner]

Originally Posted by smokeydan

I'm not sure why the manual says 3-6dB

I think it was 3 db steps for Stage Rack systems and 6 db steps with MixRack and SC48 systems, as they are a slightly "cheaper" schematic solutions.

[Sidhu]

Hello!

i am at a total loss here, the pickup point is after the AD, the return path is after the AD, why is any gain adjustment needed again ?

What am I so stupidly missing ??

I understand you want to VSC HDX recorded material now with the FW bus,
but if the recording and the playback are both using the FWx bus, are we then good, or do we still need to gain adjust ? Again, why ?

Tx a ton!
Sidhu

[digidesigner]

The path probably looks like this:

Analog Mic Gain (is regulated in steps 3/6db) > AD > Recording Picup Point > Digital Gain (to smoothen gain steps)

When you VSC, the signal is routed back where it was picked up, so any digital gain you had applied originally to your channels are reset to 0db (with FWx). So in worst case scenario you might have your "kick" drum coming back to desk (from computer) up to 5.9 db too low, as your original gain might have been analog gain plus 5.9 db of digital gain, that is now reset back to 0 from +5.9db.

Using Virtual Soundchek with HDx this digital gain offset is compensated, with FWx it's not.

Makes sense?

[Sidhu]

Ok. So I realize that the SC48 gain steps (analog) are only in the 3-6 db steps. anything inbetween is digital compensation ?

Are the steps 3 or 6db ?


This makes it rather impossible to VSC using FW i would presume...

[digidesigner]

Originally Posted by Sidhu

Ok. So I realize that the SC48 gain steps (analog) are only in the 3-6 db steps. anything inbetween is digital compensation ?

Are the steps 3 or 6db ?


This makes it rather impossible to VSC using FW i would presume...

What you can do is: take a analog signal generator (sine wave), feed the output to your desk input, connect your FW Pro Tools system, record arm the track. Start rising the gain of the channel where your signal generator is, as the level rises on the desk you can see it won't rise on your Pro Tools system (cause digital gain is bypassed), until at some point, when the analog gain is rised in the desk preamp with either 3 or 6 db step, depending on the system. When this happens, stop and mark the gain readings. Repeating this you will log all the analog gain steps only, and if you keep using only these gain settings when mixing you should be fine doing VSC with FWx

[Mike Z]

you may also want to check this thread where Sheldon has posted the offsets.

http://duc.avid.com/archive/index.php/t-224925.html

Thanks,
-Mike

[digidesigner]

Originally Posted by Mike Z

you may also want to check this thread where Sheldon has posted the offsets.

http://duc.avid.com/archive/index.php/t-224925.html

Thanks,
-Mike

Yes, but this thread seems not to include SC48 (and Mixrack?) that is newer and AFAIK has larger 6db steps, no?

EDIT: here it is, the other old thread about gain and pre's of mixrack and sc48: http://duc.avid.com/archive/index.php/t-248600.html

[Sheldon Radford]

Hi folks,

In addition to manually entering values, here's a more automated approach that uses the Standalone software and a little trick to capture the digital trim values. This trick assumes you are using SC48 or Mix Rack and FWx.

1. Load your show file into the Standalone software
2. Before making any changes, store a snapshot. Scope IN and PRE, and call this snapshot STAGE
3. Options > Devices: choose Mix Rack (even if you're using SC48) and replace the FWx card with an HDx card (right-click on the Mix Rack and choose the HDx option).
4. Options > System: choose Virtual Soundcheck Mode for inputs 1-48. This causes the gains to be compensated by a few dB. Now here's the magic part….
5. Options > System: choose Input Mode (don't go back to Stage mode first). Gains should still be showing compensated values.
6. Store a snapshot, call it PLAYBACK. Scope only the PRE setting for all channels.
7. Save this file and load it onto the actual console
8. Patchbay: assign Pro Tools inputs as the source for channels. All gains go to 0 dB.
9. Recall the PLAYBACK snapshot. Gains are now set to correct, compensated value.
10. Overwrite the PLAYBACK snapshot, and scope the IN data in addition to PRE. Now you have one snapshot that changes patch and sets the compensated gain.
11. Use the STAGE and PLAYBACK snapshots to move between input sources.

You do not need to run-through all of these steps every time you switch between Stage and Pro TOols inputs. On a day to day basis you only need to recall the PLAYBACK and STAGE snapshots, unless you've made significant gain changes. So while this may not be the answer for the guy in the heat of battle making gain changes fast and furious, it will work well for doing a daily check.

Try it out and see what you think.

Sheldon