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Old May 24th, 2009, 02:49 AM   #1
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Having to set gain too high on Mix-Pre sound mixer?

Hi

I have concerns that I'm having to set my mixer's gain too high. When I do a sound level check I have to set the mixer's gain to maximum in order to get the output meter to peak between 0 and 4 dB, even with the mic held very close to the actor's mouth.

I'm using:

Auditechnika At815b shotgun microphone and Canare Star Quad XLR cable with Neutrik connectors. These are attached to my Sound Devices Mix-Pre mixer running on 2 rechargeable NiMH AA batteries.

The mixer is set as follows:
1. PHANTOM = 15V
2. High pass filter 80/160 = OFF (centre position)
3. Limiter = OFF (centre position)
6. TAPE/RTN = RTN

The high pass filter on the microphone is turned off.

Why is the gain so high?
Am I using the wrong type of cable?
Am I using the wrong type of batteries?
Is my mixer faulty?

I've only just bought my mixer and am worried I've bought the wrong one now :(

Thanks in advance for any help
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Old May 24th, 2009, 03:40 AM   #2
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I've tried using alkaline Duracell batteries but they didn't increase the audio meter reading for speech, the maximum peak was still about 4dB with gain at maximum.

I also tried using a bog standard XLR cable, which isn't star quad, to connect my mic to the mixer and that didn't make any difference either.

With the Mix-Pre gain set to maximum surely I should get speech peaking above 4dB? Surely the levels should go much higher?

Should I have to set my gain to maximum to get 4dB peak levels on speech?
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Old May 24th, 2009, 07:59 AM   #3
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Dear Stuart,

It is highly unlikely that your mixer is defective, or you purchased the wrong one.

My first suggestion would be to try +48V phantom power.

I also suggest that you connect the output of your mixer to your camera and then send the tone signal, then set your camera's levels appropriately. Please remember that the Mixpre outputs a line level signal.

How old is your microphone?
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Last edited by Dan Keaton; May 24th, 2009 at 01:56 PM.
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Old May 24th, 2009, 07:59 AM   #4
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Hello Stuart,

What mode is your metering in?

It should be peak and RMS, not just RMS.

Regards,

Ty
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Old May 24th, 2009, 01:15 PM   #5
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Thanks for the input guys :) I'm flummoxed.

Ty:

There isn't an option for changing metering mode on the Mix-Pre. At least I can't find it in the manual and there isn't a switch on the unit. In the manual it says that the meter is peak responding showing the instantaneous output level in dBu.

Dan:

I've set my XH A1 camcorder up using the 1kHz 0dBu tone signal and it got the correct response in camera of -20dBu, I've checked in a number of threads and this is the correct response. Since the camcorder is reading the correct level with the tone signal does this mean the mixer must be okay? Or does the tone bypass certain components of the mixer?

My main concern is the low levels on the mixer rather than the camcorder. I tried +48V phantom power to the At815b microphone, but it didn't help. The mic is specified as requiring phantom power of 9-52V DC (2 mA typical) so it should be fine on 15V. My microphone is about 3 years old and has had the odd minor knock on set during production of 2 films, do you think it might be damaged? Do microphones age badly?

The full At815b mic spec can be found here:

http://www.audio-technica.com/cms/wi...6b/index.html/
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Last edited by Stuart Graham; May 24th, 2009 at 01:24 PM. Reason: missed something out
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Old May 24th, 2009, 01:56 PM   #6
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Dear Stuart,

The AT815b is a fixed-charge back plate, permanently polarized condenser.

I asked about the age of the microphone since I heard that it is possible, but highly unlikely, that this type of microphone can lose its permanent charge.

Since your microphone is relatively new, this should not be a problem.

Some microphones do better with +48V phantom power, as opposed to +12V or +15V phantom power. However, it does not seem to make any difference with your microphone.


It seems that your MixPre is working fine, based on the levels that you are seeing in your camera when you are sending tone. The tone function substitutes for the input signal from your microphone. Typically, the tone signal does not test the input stages of your MixPre.

But, there is little reason to suspect that your MixPre is not working properly.

I suggest that you set your camera gain levels using the tone function, then record, using your camera. Then bring it into your Non-Linear Editor, or play it back via your camera.

Record someone else's voice while monitoring on the headphones. Does it sound normal when you are monitoring the audio?

On Tuesday, call Sound Devices, they are very helpful.
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Old May 24th, 2009, 01:58 PM   #7
 
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Here's a long shot, but, check the wiring on your XLR cable. I've encountered mis-wired XLR cables...and it was a Canare.
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Old May 24th, 2009, 02:51 PM   #8
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Can you try another microphone and see what happens?

Do you have the mic that came with the Canon XH-A1. You can plug this directly into the mixer using the short attached cable, eliminating any possible cable problems.

Also, have you plugged the mic (using the same cable you are using to the mixer) directly into the camera? Does it give you high levels (AT mics are typically hot) or is the level low into the camera as well.

Into the camera, compare the XH-A1 mic and the 815.

If the mic and cable are okay, definitely call Sound Devices. They are very nice and will help you make sure your MixPre is setup properly and/or there is defect.
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Old May 24th, 2009, 04:10 PM   #9
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How far away from the source is the mic?

What's the source?

and have you tried different cables?

Regards,

Ty Ford

Last edited by Ty Ford; May 24th, 2009 at 07:11 PM.
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Old May 24th, 2009, 04:29 PM   #10
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The 815 I have here is not an over sensitive mic, compared to some condenser mics it is a little 'deaf'. If you compare the specs with something like a Sennheiser 416, then the sensitivity is less. So it could just be that the mixer doesn't have huge amounts of spare gain, and your mic isn't that well matched - if it produces ok results that are pretty noise free all's well, but it won't do much working at a distance.
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Old May 27th, 2009, 05:48 PM   #11
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Hey Guys thanks for the input again :)

I did lots of tests as you asked, it took me a while to get around to it what with one thing and another:

1. With the At815b mic plugged directly into camera (no mixer) using XH A1's +48V phantom:
- speaking "test 1, 2", at about 8 inches from the mic, gave much higher levels than through the mixer, high enough to make it easy to increase gain enough to clip the audio.
- this indicates to me that the microphone is functioning correctly.

2. When going through the Mix-Pre mixer connected to the camcorder you must increase the mixer's gain to maximum and minimise the attenuation on the XH A1 in order to get speech levels to peak at about -12dB on the XH A1 (with the mic held at the same range as in 1.).
- Considering that on set the talent could be considerably further from the mic, to keep it out of frame, is this high enough for recording good audio?

3. Plugging headphones into the camcorder when not using the mixer gave a great deal of hiss which is not apparent after recording to tape and playing back in a NLE. However, listening to a recording through headphones connected to the camera when the mixer's preamps are used gives very little hiss. Presumably the camera preamps interfere with the camera headphone circuitry.

4. Alternating between Canare/Neutrik and generic XLR cables made no difference to the audio response registering on the mixer or in the camera.

5. Alternating between the mixer's +15V and +48V phantom power made no difference to the audio levels. Though perhaps speech had a little more presence at +48V - this is very subjective and I might have imagined it!

6. Using the microphone and mixer connected to the camera with the line/mic switch on the camera set to mic gave huge noise levels and terrible sound. This generates unusable audio even after lowering the gain.
- in short, using the camera's mic setting to boost the input from the Mix-Pre mixer is a no-no.

I haven't got another mic to try at the moment, but I do have one on order (An Oktava MK-012) so I'll test its response on the mixer when it comes.

I've recorded audio directly into the camcorder and into the camcorder via the mixer, perhaps I could try to post the files on here for you guys to listen to and see what you think. I'm not sure if you can post audio or not...

The mic seems fine. So I think that either the mic is not very compatible with the Mix-Pre (because the levels won't go very high on the mixer) or my mixer is defective. What do you guys think?

Thanks again chaps!
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Old May 27th, 2009, 06:03 PM   #12
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Hmmm,

I suspect it's broken, not incompatible. Go back to where you bought it and let them know.

Good detective work.

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Old May 28th, 2009, 09:53 AM   #13
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Look at your Mix-Pre's external power jack. If the jack is a simple co-axial DC connector, then you have an original model Mix-Pre and the outputs are impedence-balanced but the entire signal is carried on pin 2 of the XLR. This can give odd results with some line-level camera inputs. Regular attenuators also don't work correctly with this older model, so you couldn't use regular attenuators to test again using the camera's mic-level input.
If your Mix-Pre has a 4-pin external DC jack, then it's a new model with conventional balanced outputs. In that case, then perhaps the camera's line-level inputs are extremely insensitive. You could however use regular attenuators on the output of the Mix-Pre and test the camera at mic-level or mic-attenuated level.
Do you have another line-level output source you can connect to the camera and test that to get an idea of how sensitive the camera is at line-level?
The AT815b is not tremendously sensitive like some models, the AT4073a for example. Since the Mix-Pre doesn't have a Master output control, I have to use a lot of input gain when hooked to less sensitive mics. However the Mix-Pre should be putting out enough signal unless the camera's line-level input needs a lot more signal than normal.
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Old May 28th, 2009, 10:18 AM   #14
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It would not hurt to call the very nice tech people at Sound Devices and ask what the optimal settings are for your setup. Getting this pinned down would make it easier to objectively judge the other elements in your system.
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Old May 28th, 2009, 12:24 PM   #15
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I can tell you that I have used the AT815 with the MixPre (feeding an HVX-200) and did not experience the problems you are describing. SO it is NOT the combination of the 815 and the MixPre standing alone.

Chris
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