GH3 Audio Input & External Mics – Wiring, Impedance… Incompetence?

[Guy Mcloughlin]

The GH3 audio level setting is really an AGC-Boost control, where the AGC boost is +3 dB when the camera is set to 1, and goes up to +20 dB at level 19.

The native noise floor for the GH3 is -66 dB RMS, which is quite good for a DSLR, but you have to set the camera’s audio level to 1 and feed the camera a strong -15 dB signal to realize the full 66 dB range. This means you need to use a good external mic pre-amp or mixer to achieve a low-noise recording with the GH3.

On the low-cost side of things, the JuicedLink Riggy RM222 mic pre-amp would be a good match for the GH3. It provides up to 30 dB of clean gain, along with phantom power for professional mics. ( RM222 costs about $330 )

Moving up in price, you might want to take a look at the Sound Devices MixPre-D mixer, which offers a huge range of professional features, but will set you back about $900.

Also, remember to set your GH3 to use the 50 Mbps MOV shooting mode which records audio in uncompressed LPCM format. This mode records a higher quality video image and the best audio this camera can produce.

…One last option is to use a low-cost portable recorder like the Tascam DR-40 which has reasonable mic pre-amps ( just don’t go past level 65, or you will start to hear noise in your recordings ) and can supply phantom power to professional mics. The Tascam DR-40 sells for about $140 at B&H Photo in New York.

[Al Bergstein]

What Guy Said. (G). Also, I have a 5Dmkiii and it runs fine with the Mixpre-d when I need two mics. I can turn off the AGC, and I assume that the newer GH3 allows the same, but Guy’s thoughts are likely correct. The GH3 seems to be a fabulous camera for the price, a good friend got one.

Question for Ty: I have that splitter cable, but doesn’t that cut the signal strength in half also, meaning more gain and likely more hiss? I read that somewhere after buying the cable. Of course, hiss removal is relatively simple these days.

Al

[Bill Bruner]

I have this camera, and I plug powered XLR mics into it all the time. You have to match impedances though. The problem with a straight through adapter is that pro mics are at about 600ohms, while consumer cameras and camcorders are at about 2500ohms.

Joe – I hope you’re not getting “hum” with Eric’s DIY solution – but if you are, you may want to invest $17 in a Hosa XLR to 3.5mm impedance matching adapter.

Here is my GH3 with a battery powered Audio Technica AT835 and the Hosa adapter. Works like a champ:

Hope this is helpful,

Bill
Hybrid Camera Revolution

[Ty Ford]

Excuse me Bill,

Back in Bell Labs day, that’s the way things were. There may (or may not) be mechanical reasons why the connectors work better, but Impedance matching in this case is not an issue.

The thumb rule for impedances is, low to high is OK. High to low is a NO.

Visually, you can flow a low impedance circuit (think 6″ pipe) into a high impedance (garden hose) and get a nice flow. If you go high (garden hose) into low (6″ pipe) it just doesn’t work.

Regards,

Ty Ford
Cow Audio Forum LEader.

Want better production audio?: Ty Ford’s Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford’s Blog

[Kyle Brandson]

One question,

So are you saying that if I just use a basic converter cable like this:
https://www.amazon.com/HOSA-XLR-Female-3-5mm-Sleeve/dp/B000068NZF/ref=sr_1_5?ie=UTF8&qid=1365951871&sr=8-5&keywords=xlr+to+3.5mm
I can use a rode ntg 2 with a GH3? I am also thinking about getting this camera and a mic, but I don’t want to buy Rode Videomic or the Panasonic microphone as I want to use a good-for-all mic for recording separate audio for example with a boom pole, in quality video making. Just in case I don’t have the space or the chance to use a separate recorder like a zoom h4n, I would mount the mic on the camera and record directly on it.

Thanks, Kyle

[Luke Seerveld]

I’m not a real sound guy, but sometimes get called upon to record sound for interviews. I record directly to a Zoom H4N or through a Sound Devices 302 mixer to the Zoom. When I was using the GH2 I had a friend make up a cable that went from the tape out on the 302 to a male mini 2.5mm, but with a pad to bring the line level of the mixer to the mic level of the camera. This worked well. Recently, I had a vendor custom make a similar cable for the GH3 from 302 to male mini 3.5mm, but I can’t tell if the pad is there.

When I set the camera mic level to 1 or 6 or higher and hit the tone switch on the 302, the same volume appears on the tiny camera audio meters. Why is this? Then it seems like if I go anywhere above 0 on the mixer I get distortion on the camera’s recorded audio… there’s no headroom.

I’m figuring the pad was maybe not put in after all, but either way, I seem to be missing something. Any thoughts?

Needless to say, I’ll continue to record double system to be safe.

[Joseph Moore]

My initial experience using powered mics with my GH3 and a Beachtek DXA-2T (an unpowered adapter) has been quite poor. I thought I could save a few bucks since all my mics are powered, but maybe not.

The the GH3’s levels turned all the way to 0 and the DXA-2T trim controls wide open I got almost no sound level from a Rode NTG2 or a Shure SM58.

I had to turn the levels on the GH3 all the way up to end up with any signal. Obviously, the noise floor was horrible. Amazingly I was able to rescue it enough in post to be usable, but not a good experience at all.

I don’t know what I’m doing wrong, or if some piece in the chain is defective. I’ve got to do some more testing, but my initial thought is that I need an adapter with power, like the Riggy222.

[Joseph Moore]

So I did a bit more testing today with another powered mic, and it really does seem that the problem is that their just isn’t enough juice coming from the mic through the Beachtek to yield much signal.

I left the GH3’s levels at their lowest (1) as recommended and did some recordings. Virtually nothing showed on the GH3’s on-screen meters, but once I got the audio into Audition there was a clean recording…it’s just that the audio levels were very, very low. I was able to normalize them and get a usable recording (better than I got by cranking the gain on the camera) but this is definitely not how you would want to record…if for no other reason than it is virtually impossible to monitor anything while recording.

How does my experience compare with others using other non-amplified adapters?

[Richard Jett]

Guy,
I am trying a audio setup with the Zoom H4n and the GH3. Line out from the zoom to camera mic in but I need a pad. Do you know of a cable that has one?
Thanks RJ

[Ty Ford]

Hello Richard and welcome to the Cow Audio Forum.

In the future, it would probably be a good idea to start your own thread in stead of glomming on to an old one.

What’s a GH3?

You’re trying to send audio from the Zoom to the GH3.

Are you trying to use the Hn4 as a mic to feed the GH3?

What are you trying to do?

Regards,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford’s Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford’s Blog