-20db ref calibration on an HMC150

[Justyn]

The HMC is a bit more selective and finicky about the audio so some loud bass or a really strong line input can be tough to deal with. But the worst part is the headphone input.. it's really really noisy and gives sometimes a false reading on the level of noise as a whole..

 

[Denwa]

Make sure you carefully moniti=or your recordings. In my experience with 2 HMCs (posted on 'User somewhere), the HMC has a pretty low headroom on the input signal, and introduces distortion REGARDLESS OF THE METER READINGS when the input signal passes that threshold (in my tests, around +10 dBU) (see http://www.dvxuser.com/V6/showpost.php?p=1622274&postcount=181)... by setting a nominal level of -20dBFS, you have a greater risk of this problem rearing its head. I don't know if all HMCs have such a low input clipping point (none of the HVXs or DVXs I've used do), but I's say you should definitely experiement to see if your particular HMC is "safe" for operation when configured that way... on mine, e.g., I've determined that one dot below 12 o'clock on the gain dial is the lowest safe gain setting on the camera I can use to be sure that the meters will indicate clipping and the limiters will have the desired effect.... at that level of camera gain, I have to calibrate my mixer quite differently (+10 dbu on the mixer needs to be below 0dBFS, so 0 dBu at the mixer would be -10dBFS on the camera; -8dBu at the mixer would be -20dBFS on the camera. You can see how calibrating 0dbu as -20dBFS would NOT WORK for at least my particular 2 HMCs...

ullanta. If your mixer has a variable output level (adjusted in the mixer not just the master gain comtrol) could you not lower the gain about 10dB? Then at -20 (or whatever you are calibrating to) the input levels would be lower but you could still calibrate your mixer to the camera without clipping the input?

Panasonic claims a 0dBu level but I wonder if it is really not more like the cheaper prosumers that are what -10dbV? (Same reason the psc promix3 has that output gain adjustment from 0 to -10 - screwdriver adjustment) The ENG-44 has adjustable resisters inside the mixer for anyone who wants to play with those. Do a google search on that. (probably voids warranty).


I am getting an old Audio Technica AT4462 (I hope that wasn't a mistake but it was only $350) and will check my audio when I do.
(BTW if ANYONE has info on that mixer please let me know!)

 

[ullanta]

Right... many mixers will let you attenuate the output, which would let you match optimally to the HMC (or any camera). Or you could use pads between the mixer and the camera inputs (if the mixer doesn't have built-in output attenuation).

(Or, you can just keep levels lower on the mixer, though that would reduce the usefulness of the mixer's metering and output limiters).

I think Panasonic's claim of 0dBu is a maximum, while standard +4 and -10 ratings are nominal... that is, a device rated as a +4 dBu nominal output may pump out +30 on a strong signal. So Panasonic's 0dBu spec is pretty low, given that most pro gear is a NOMINAL +4....

 

[Denwa]

Right... many mixers will let you attenuate the output, which would let you match optimally to the HMC (or any camera). Or you could use pads between the mixer and the camera inputs (if the mixer doesn't have built-in output attenuation).

(Or, you can just keep levels lower on the mixer, though that would reduce the usefulness of the mixer's metering and output limiters).

I think Panasonic's claim of 0dBu is a maximum, while standard +4 and -10 ratings are nominal... that is, a device rated as a +4 dBu nominal output may pump out +30 on a strong signal. So Panasonic's 0dBu spec is pretty low, given that most pro gear is a NOMINAL +4....

I've noticed Sound Devices mixers are defaulting to 0dBu (of course adjustable to +4, +6 etc). Likely since so many are being used with prosumer cameras and recorders. I really wish Panasonic would have just went with +4dBu on these cams.

I lowered the output on my mixer.

For those on here that were wondering why you use -20db as a standard (-18dbfs in europe). The peaks are supposed to exceed -20 on the camera. Most North American equipment uses Vu meters and they do not show peaks well, as they are a volume averaging meter. So tone at 0vu lined up to -20dbfs on the camera is not the same as peaks from dialog showing 0 on the mixer. Those peaks can easily reach clipping if the camera is calibrated at -12.


If using a Vu mter on the mixer and claibtrated at -20 you want the top end of teh vu meter to read about -4 to +2, that should elave you with peaks on most dialog sources around -12dbfs to -6 dbfs.

If using a PPM meter you want the peaks around -2 to +8.

Some mixers like Sound Devices have the option of a Vu/PPM hybrid meter which shows both. I really like these as they show you what the peaks are really at and an average volume level.