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Sound Devices MixPre-D - is it working properly?

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Jonathan Hardison
Sound Devices MixPre-D - is it working properly?
on May 17, 2016 at 6:38:33 pm

Just snagged one of these from ebay. This is my first piece of pro audio gear. I do videography work, mostly live events, and I needed a decent pre-amp since the pre-amps in my Tascam DR-100 weren't quite cutting it.

I notice when I have the headphone level set to 0db and have no mic connected or a mic connected and not set to phantom power (my mic needs phantom power) I start to hear a little noise/hiss with the gain pot set to 11 o-clock and hear noticeable noise/hiss from 1 o-clock to max gain.

I also notice with a quick recording into Adobe audition via the USB interface, I get the same result - slight bit of noise/hiss in the recording past 60% gain with no mic attached.

Doesn't sound like interference, just like I hit the noise floor. I suspect that a unit with this much gain simply is supposed to work this way, but I wanted to see if you had any experience in sound and could just confirm. It's possible that there's no such thing as a pre-amp with zero noise with the gain set to 60% or higher, but again, I'm new to this, so I simply don't have any point of reference.

Can anyone confirm that this is normal operation for this device, or should I get it serviced?

Thanks so much!

Jonathan


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Bruce Watson
Re: Sound Devices MixPre-D - is it working properly?
on May 17, 2016 at 7:04:58 pm

[Jonathan Hardison] "Can anyone confirm that this is normal operation for this device, or should I get it serviced?"

It's not normal to "use" the unit without a mic, no. Try using a mic before you decide it's defective.


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Jonathan Hardison
Re: Sound Devices MixPre-D - is it working properly?
on May 17, 2016 at 7:14:28 pm

I get the same noise with or without a mic. I'm trying to set a baseline.

Say, for instance, is there any such thing as a pre-amp that has no noise/hiss at all when set to 100% gain?

Thanks!


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Bruce Watson
Re: Sound Devices MixPre-D - is it working properly?
on May 17, 2016 at 9:30:49 pm

[Jonathan Hardison] "I get the same noise with or without a mic."

Really? Because there's a world of difference between an open circuit and a low impedance microphone. A microphone is low impedance so that real physical current flows in the wires going to the mic. The micpre the microphone is connected to typically has a higher impedance so that this current can develop sufficient voltage that the micpre has something to amplify. Without this voltage across the input to the micpre, the micpre is operating outside its design specifications. Said another way, without an input voltage, the output of the micpre is largely undefined.

I'm just saying that you can't meaningfully "set a baseline" for a micpre using an open circuit.


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Jonathan Hardison
Re: Sound Devices MixPre-D - is it working properly?
on May 17, 2016 at 9:57:46 pm

That's good to know. Makes sense.

I guess a better worded version of my question is:

Can anyone who has experience with a MixPre-d, a Sennheiser ME66/K6 shotgun and Sony 7506 headphones confirm if you get any noise while phantom powering the mic, setting the headphone level to 0db and cranking the gain to 100% in a quiet room? Do you get that same noise at 100% gain from a recording with the unit plugged into a computer via USB?

I may be naive in expecting a pre-amp to have no noise at higher gain levels using the microphone that I'm using, but I have no frame of reference, which is why I'm asking.

Thanks again!

Jonathan


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Bill Davis
Re: Sound Devices MixPre-D - is it working properly?
on May 18, 2016 at 12:18:38 am

One thing you need to understand is that most level control circuits are logarithmic, not linear.

As the control gets toward the top of the scale, (or the bottom for that matter) the boost or cut is increased much more rapidly than on a strict 1 to 1 basis.

Look at the db readings and you'll see that at the extremes, theres typically a LOT more cut or boost than there is near the zero position. Which could mean that at the 100% boost position, you're getting a LOT of gain added to accommodate the HUGE difference between, for example, the amplitude of a line level signal and a mic level signal. Those two things are VERY different. So a fader designed to handle both, needs a BIG range of boost and cut over it's travel.

So "turning it up to 100" is often NOT a particularly sensible way to operate a mixer.

Obviously, all this depends on how the particular circuits are designed. But just because the fader travels 6 inches that doesn't mean that the first inch is simply six times quieter than the 6th inch. It typically doesn't work that way.

FWIW.

New signature under construction and coming soon. Please stand by...


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Jonathan Hardison
Re: Sound Devices MixPre-D - is it working properly?
on May 18, 2016 at 2:01:03 am

I'm simply trying to figure out if my mixer is operating properly, or if there is an undue amount of noise.

Is there a way to do that?

Thanks!


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Al Bergstein
Re: Sound Devices MixPre-D - is it working properly?
on May 18, 2016 at 2:01:06 pm

i have one, I'll check later this AM. I don't believe this is normal behavior. Just used mine Sunday and did not hear hiss at all.

Al


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Al Bergstein
Re: Sound Devices MixPre-D - is it working properly?
on May 18, 2016 at 2:17:34 pm

I just checked it out. No. At 11 O'clock position, there is no noise floor at all. First off, check your batteries to make sure they are good. I always put a meter on them and they should be above 1.3V. Below that I often notice noise on various devices, like mics that use batteries instead of phantom. If you use fresh batteries and are still getting a noise floor at 11 with a mic attached, contact Sound Devices and have them service it.

Al


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Jonathan Hardison
Re: Sound Devices MixPre-D - is it working properly?
on May 18, 2016 at 7:13:50 pm

Thanks a ton, Al. That's really helpful. Could you verify that you had your headphones at 0 db? I don't hear any hiss at 11:00 with the headphone output at -12db.

Thanks again!

Jonathan


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Al Bergstein
Re: Sound Devices MixPre-D - is it working properly?
on May 18, 2016 at 7:28:53 pm

No. I hear no hiss when I plug in my headphones, dial in 0 dB for them, and have my gain control for the mic at 11:00. I'm using batteries on both the unit and the mic ( an AT897) that read at or over 1.35V. There's a sound floor that shows up close to +20 but it should.

Al


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Al Bergstein
Re: Sound Devices MixPre-D - is it working properly?
on May 18, 2016 at 7:37:19 pm

And I am also using Sony MDR-7506 headphones. My experience is that the MixPre-D noticeably improves such devices as a Zoom H4 and H5n which seem to have pre's that are a bit 'harsh" to my ears. When run through the mixpre prior to the recorders, the output seems more rounded at least to these ears. For comparison, I do not seem to need the mixpre for my Marantz PMD661. The pre's in that seem fine.

Again, make sure you are using fresh batteries or plugged into AC.

Al


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Craig Alan
Re: Sound Devices MixPre-D - is it working properly?
on May 21, 2016 at 11:10:56 pm

This is very hard to diagnose from even a detailed description. Audio is a chain and any component of the chain can add noise. To isolate the problem you need to swap out each variable to see if it corrects the problem.
Try a different mike. Try a different interconnect .

My experience with the mixer is that it is underpowered. Better when providing phantom than dynamic mikes. But I understand why you are setting gain at 100%. I find that SD mixers generally are very quiet and boosting the gain doesn't usually add noticeable noise. If you posted a sample I think it would be easier for anyone trying to tell you if it was a defective unit would have a better understanding of how much hiss is in the signal. Ive had trouble with that mike as well. The way it screws apart and can create problems in certain units.

Are you shooting indoors or out? Cause for indoors I prefer the Audio-Technica Hypercardioid Condenser Microphones.

Mac Pro, macbook pro, Imacs (i7); Canon 5D Mark III/70D, Panasonic AG-HPX170/AG-HPX250P, Canon HV40, Sony Z7U/VX2000/PD170; FCP 6 certified; FCP X write professionally for a variety of media; teach video production in L.A.


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Jonathan Hardison
Re: Sound Devices MixPre-D - is it working properly?
on Jun 12, 2016 at 1:15:51 am

Sent it off to Sound Devices for service and they said it's working properly. Were even nice enough to waive the service fee since they didn't have to take it apart.

I guess I didn't know what to expect when using one of these units. With my Tascam DR-100 I'd set the (I'm assuming digital) gain to Medium - anything higher gave me too much noise - and then would have to crank the gain way up in post. Never ran into any appreciable extra noise doing this, but I suppose I had the gain pretty low.

I assume there is no such thing as a pre-amp without *some* self noise. Does everyone always use a de-hiss, de-noiser or some other cleanup tool in post? I figured out how to capture a sound print of the amp noise in Audition using the hiss-reduction tool. Seems to work pretty well.


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Bruce Watson
Re: Sound Devices MixPre-D - is it working properly?
on Jun 15, 2016 at 9:46:06 pm

[Jonathan Hardison] "Does everyone always use a de-hiss, de-noiser or some other cleanup tool in post?"

I'm using my MixPre-D with Oscar SoundTech 802 lavs (almost always with the OST XLR power supply, but when there's no other way I use Sennheiser G3 radios with the 802s), an AT 4053b, a Sennheiser MKH 416, and an E-V RE50N/D-B dynamic reporter's mic. Serviceable stuff, but clearly not state-of-the-art. I typically take the output from the MixPre-D's unbalanced mic output directly into camera (if the cameras could take XLR line-in, I would, but they can't). But I calibrate the main camera with the MixPre-D's 1kHz tone resulting in negligible noise from the camera.

After I figured out how to set my system up, do proper gain staging on it, and record dialog well (mic placement), I've never needed to remove hiss from my dialog. I have used de-noise applications/plugins for unwanted background noise (HVAC, traffic, etc.), but not to remove any pre-amp hiss from either MixPre-D or camera, or for that matter microphone self noise. Never had a client mention it, ask for it, or complain about it.

IMHO, the least likely source of hiss is your MixPre-D. And SD has given your unit a clean bill of health. Time to start looking other places.


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Al Bergstein
Re: Sound Devices MixPre-D - is it working properly?
on Jun 29, 2016 at 3:58:24 pm

Just read the updates on this. Yes, Bruce is right, the SD is likely not the cause of your problem. You mentioning the Tascam is more likely the cause. I have both and the Tascam's are noticeably more noisy than the SD. Follow Bruce's advice and set it up to isolate each part of the chain. Notice his discussion of calibrating the HDSLR to the SD with the 1kHz tone. That's real good advice. Try calibrating the Tascam to the tone from the SD. Good luck!

Al


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Allen Cavedo
Re: Sound Devices MixPre-D - is it working properly?
on Jul 9, 2016 at 4:09:27 pm

Even though SD serviced your unit, let me answer as you asked using my MixPre-D: "I notice when I have the headphone level set to 0db and have no mic connected or a mic connected and not set to phantom power (my mic needs phantom power) I start to hear a little noise/hiss with the gain pot set to 11 o-clock and hear noticeable noise/hiss from 1 o-clock to max gain."

Using no mic plugged into Input 1 with 48v turned on, I got the same results as you did, meaning yes there is normal preamp self noise at 11 and 1 o'clock. Using a Sennheiser MKH8020 (very low self noise) I heard similar self noise as you did, only probably less due to the mic I used.

The point is that all preamps have self noise, the more you pay, generally the less there is. SD uses excellent components and make great preamps designed for battery powered field use. The MPD mixer is without question very good in all respects. Hard to find a field mixer with better specs or performance. The SD 302 is slightly better on paper but I doubt you could hear the difference. You have a best-in-class professional piece of gear, quit worrying, it's awesome.

Little known fact: you can buy a $30 Apple USB Camera to Lightning adapter, with a short USB cable plug it into the USB output of the MPD, plug the Lightning connector into an iPhone, fire up RodeRec or other recording App, and record awesomely high quality sound! Also only way I know to get stereo sound INTO an iPhone.


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