Question on setting MixPre tone to camera

Gohanto

Gohanto

Veteran
I did location and post sound on a 48 hour film this last weekend (first time since I bought a MixPre I've used it). Levels turned out fine, but on some door slams I clipped. I set levels to -16 dBFS at the camera with the 1kHz tone (we tried running 2 cables and tone to -12 and -20, although for some reason the cam's 2nd input wouldn't work, so we split the difference)

Doing some more investigating...
MixPre's limiters are initially set to +18dBu (adjustable by screwdriver so there doesn't seem to be a reliable way to set the limiters to a known value, especially with them recessed and hard to see)
And I've seen pretty common advice here to just set the 1kHz tone to -12dBFS in other threads, but that would clip @ the camera before even hitting the limiter.

So...
1. Is there a good way to set the limiter on the MixPre for a camera setting of -12dBFS?
2. Or is there ever likely to be a problem recording to camera from the MixPre using -20dBFS? (I've heard this to be great with 24bit recording, but 16bit audio seems more of a split decision)
 
Gohanto said:
I did location and post sound on a 48 hour film this last weekend (first time since I bought a MixPre I've used it). Levels turned out fine, but on some door slams I clipped. I set levels to -16 dBFS at the camera with the 1kHz tone (we tried running 2 cables and tone to -12 and -20, although for some reason the cam's 2nd input wouldn't work, so we split the difference)

Doing some more investigating...
MixPre's limiters are initially set to +18dBu (adjustable by screwdriver so there doesn't seem to be a reliable way to set the limiters to a known value, especially with them recessed and hard to see)
And I've seen pretty common advice here to just set the 1kHz tone to -12dBFS in other threads, but that would clip @ the camera before even hitting the limiter.

So...
1. Is there a good way to set the limiter on the MixPre for a camera setting of -12dBFS?
2. Or is there ever likely to be a problem recording to camera from the MixPre using -20dBFS? (I've heard this to be great with 24bit recording, but 16bit audio seems more of a split decision)
Click to expand...
set 0 to -20 its a standard for a reason.
That doesnt mean you cant go above 0 on your mixer.
I do know the metering isnt the greatest on the miix pre, but on the 442 and 302 i hit +12 giving me peaks on camera around -10/-8

What camera were you using? Not saying its the case but a lot of cameras
the headphone amp will clip before whats on tape.

Plenty of ways of adjusting your limiter.
Open a mic into a constant sound source, plug into the camera..
adjust the limiter and watch how its affected and do the math to figure out
where you want it.
 
We were using an HVX, but I had the monitor directly off the MixPre because the headphone jack was broken on it.

I'm aware that I can go over 0 on the mixer, but it was in FCP that I noticed the signal clipped (at this point I had the conversation
- me: when we did the door slam, did you watch the levels on the camera?
- dp-yeah.
- me-did they flash red?
- dp-yeah, but only for a second, so I figured it was okay.
Lesson: I'll trust DPs a little less in the future. It's really my job anyway.)

During the shot the MixPre limiter light turned orange, but never red. So I figured I was safe.

Hadn't thought about just using an external constant tone to set the limiter. Thanks.

Have you ever had an issues setting 0 to -20 on 16-bit vs. 24-bit?
 
I 100% always set tone on any camera at -20
Its just a reference marking and also where the camera likes to see .775 volts

Its all about putting a solid hot signal into the camera at that reference.
If I was peaking at 0 on a field mixer i would be way too low at camera.
That was great back in the analog days but peak at +10ish on the mixer, -12/-8 on camera and you're golden.

With the limited metering above 0 on your mixer that gets a little rougher (but not horrible)

Hint for ya, on most of the smaller camers (HVX included) you can get a cleaner (less noisy)
signal from the camera out of the RCA's . I have a simple female 1/8 stereo jack to
2 mono L/R male rca's that I plug my return of my breakaway cable into.
Leaves the headphone jack empty as well so on playbacks you hear it out the rca's back to your mixer, but they can also hear it out of the speaker at camera.
 
Hmmm.... That seems kinda obvious now but it never occurred to me to just mix at a hotter level (I was running average level of around 0 to +4ish)

I've -30,-15, 0,+4,+8,+12,+16dBu LEDs, plus limiter and clip LEDs, which (imho) gives me a semi-reasonable idea of what's going on, but I agree more would certainly be nicer.

And thanks for the tip on RCA jacks. I'll definitely look into that for future shoots.
 
I dont use the mixpre, but I just looked up the manual and according to what I just read
those limiter adjustments are for the INPUT channels.
Am I reading this correctly that there are NO output limiters?
(im dead tired at the moment so I might be having a "duh" moment)

And if you're lighting up the INPUT limiters..bad...very bad.
You're crushing your signal.
Once again going on reference of the 302 and 442..

but since this seems to be your only limiters..yea I guess I would hit them occasionally on your mixer, where I would avoid it on the other mixers.
 
Last edited:
It is a little tricky in the MixPre manual, but the LEDs show limiting on the input and the output.
From the manual...
"This clip circuit monitors both the front end gain stage and the variable gain stage. If the audio signal clips anywhere, this LED will show it. When the limiter is activated, the input LED’s illuminate amber in proportion to limiting action."

Since they advertise the inputs as "unclippable" I'd hope it's the output I was almost clipping. And the only time I was near that was during a door slam. (which I clipped red on the first take, brought it down and it orange on the 2nd take, and the director was happy and didn't want to do another)
 
roomtone said:
Rippie:

Nice tip about the RCA jacks on the HVX.

Thanks for sharing.
Click to expand...
no prob.
just realize you need to plug it into a return of a mixer to get the volume out of it.
You cant just plug headphones right into the rca outs.
 
Last edited:
Everything Ripple said is what I would as a rule do. But the MixPre is a bit quirky. As you found out the limiters while great(my opinion) are a royal pain to set anywhere specific. And the MixPre meters only go to +16dBu but the clip point is +22dBu and the limiters wide open are at +18dBu. Plus it's all in dBu not VU and actually the norm if I remember correctly is 0VU = -20dBfs, and with out looking things up I'm not sure exactly how that translates to the dBu that SD uses.

What I do for FX recording is leave the limiters wide open (at +18) and set the recorders inputs so that it's "clip proof" and mark that spot. I send tone and see where that ends up on the recorder, so I can get back to that setting when needed. On the Marantz 671 this point turns out to be just at -20. Which is pretty much what Ripple was saying since the Marantz is a full Scale meter so -20 should be 0VU. When I did this wit the DVX100 tones from the MixPre were at two bars on it's (if I remember correctly) unmarked meters. The camera man though this was way too low. They "corrected" my setting on one shot and were completely blown out when folks started yelling. But because I'm a firm believer in CYA I was splitting to the marantz and those tracks were fine. In FX I will often ride the recorder up when I know that I won't be getting loud, but I have the mark and tone to get me back in failsafe mode.

And yes the MixPre has input and out put limiting, actually I think the limiting is always at the input but it monitors the out put and the output can trigger the limiting. Anyway the LED's above the inputs light up if the input is triggering the limiting and the output LED turns red if the out put is triggering the limiting.
 
The MixPre has a peak reading meter, calibrated in dBu. For a sinewave tone, an averaging meter (VU) and a peak reading meter will indicate the same level but for complex waveforms such as speech the two meters diverge, with the peak meter reading higher than the VU meter. For speech the two will differ by roughly 8dB or so.

SMPTE specs call for 0VU = +4dBu = -20dBFS. EBU specs call for 0VU = 0dBu = -18dBFS. The MixPRe's meters are calibrated so that 0 = 0dBu (0.775v) and that's the level at which it sends tone. But when recording speech, music, etc the MixPre's peak reading meter will indicate around +8 or even +12 when sending the same average level signal to the camera. So setting tone to -20 or -18 in the camera, then recording speech in the +8 range on the MixPre's meters will result in speech levels in the camera's (usually) peak reading meters around -10.

The SD442 has a dual mode meter that can optionally display both average levels (VU) and peak level simultaneously and a few minutes watching its eter with different signal sources is highly instructive. The average level is shown as a continuously illuminated strip of LEDs from left to right. The peak level is shown as a single illuminated LED to the right of that strip. On tone from the internal generator or a tone plug on an input, the peak dissappears because it coincides with the top LED of the average. Yet with real world signals the relationship between average and peak is very apparent when you use one of the combination modes.
 
You must log in or register to reply here.
Back
Top