GH4 audio bug discovered

[HDWarrior]

This is not apparent in the UK version of the GH4 though I would never run the sound up full blast at any point in time. I will do some more testing in the morning its 2am in the UK.

 

[stoneinapond]

• The buzz is always there: It is present whether or not a microphone is plugged into the GH4 and at all audio gain levels.

With no external microphone plugged in (just listening to the internal microphones) I don't hear any buzz at any gain level. Perhaps if I took into an anechoic chamber I might discern something.....

 

[Sol M.]

...But this audio has been boosted in post, hasn't it ?

Meaning if you took a raw video clip and threw it on your NLE you would not hear the buzz at this level without boosting the audio levels. Yes?

As I said, the audio has been normalized.

 

[TheDingo]

This is not apparent in the UK version of the GH4 though I would never run the sound up full blast at any point in time. I will do some more testing in the morning its 2am in the UK.

Hi Philip,

I honestly think that people might be boosting the audio levels in post to the point where the noise-floor is clearly audible, which is always going to sound bad.

For noise-floor tests I do the following:

1- Connect my camera to a Sound Devices Mixer ( an equivalent mixer will do ), which has a dynamic range of 110 dB or more.

2- DO NOT connect any mics to the mixer. You should just have one cable going from the mixer to your camera.

3- Turn on the SD mixer's 1 kHz test-tone, and adjust your camera's audio gain until the mixer's test tone is recording at -12 dB.

4- Start recording the SD mixer's test-tone for 10 seconds, then turn OFF the test-tone but KEEP recording for another 20 - 60 seconds. ( you will be recording calibrated silence once the test-tone has been shut off )

5- Bring your recorded footage into your NLE, and check to see where the audio meters in your NLE sit while the test-tone is playing. The meters should be close to -12 dB, if not repeat the test and adjust the camera gain accordingly.

6- Note where your NLE audio meters sit once the mixer's test-tone has been shut off. This is your camera's true noise-floor. Using Sony Vegas Pro, I'm seeing a noise-floor of -63 dB RMS for the GH3 and GH4.

I personally consider any noise-floor above -60 dB RMS to be less than ideal, which means you don't have much audio room to boost GH3 or GH4 signals if you want to maintain this inaudible noise-floor.

Portable audio recorders like the Olympus LS-11 / LS-12 / LS-14, Sony PCM-M10, Tascam DR-07 Mk2 / DR-40 / DR-100 Mk2 will all show a noise-floor of -75 dB RMS or better, which means you have at least 15 dB of room to boost the audio signal in post and still maintain an inaudible noise-floor. Professional recorders like the Sound Devices models go way beyond -75 dB RMS, so you could boost their true noise-floor by 40 dB and still have an inaudible noise floor.

In the real-world the self noise you record from microphones ( or ambient room noise ) will obliterate these very low noise floors, but the main advantage of these low noise-floor recordings happens when you f*ck-up a recording and record it 20 or 30 dB too low. With a high quality recorder you can boost the recording by 30 dB, and you still can't hear the noise-floor. With cheaper audio gear, their own self-noise obliterates any audio recorded quieter, so you are limited by the self-noise of the recorder. ( or in this case the GH4 camera )

 

[TheDingo]

As I said, the audio has been normalized.

I personally consider "normalizing" dangerous, as normalizing a quiet sound will usually boost the audio levels far too much and destroy any audio integrity the recording originally had. ( like the horrible in camera AGC circuitry does )

In other words, normalizing can make good audio sound like sh*t.

I strongly recommend using linear audio boosts and careful compression to maintain the quality of the original recording. I also use noise-reduction passes to remove some of the recorded noise in situations where I know that the ambient room noise is going to be too high, or when I've accidentally recorded my audio too low.

The GH3 and GH4 are very unforgiving of low audio levels because of their own high self-noise ( they are still better than their competitors, my Canon 60D had a noise-floor of -52 dB and I could always hear the dang hiss. In many cases the Magic Lantern hack can fix this for Canon cameras ), which cannot stand much boosting in post. If you record your audio with levels 10 dB too low, then you run the risk of hearing the noise-floor when boosting the audio levels back to what they should have been. ( assuming high quality listening environments )

 

[Sol M.]

Here is a video containing a series of tests of the Panasonic GH4's audio buzz issue. The GH4's LCD and headphone output was recorded while the camera's settings were adjusted to test the effects of different settings on the buzz.

GH4 Settings:

• Mic gain: +6dB
• Headphone Volume: 15
• Recording Mode: 1080/60P/100mbps/MOV

Audio is straight from the camera. No additional audio processing in post.

 

[TheDingo]

Here is a video containing a series of tests of the Panasonic GH4's audio buzz issue. The GH4's LCD and headphone output was recorded while the camera's settings were adjusted to test the effects of different settings on the buzz.

By recording the headphone output, this is still boosting the audio levels so high that you're clearly hearing how the camera setting will alter the camera's noise-floor. ( the actual self-noise of the camera ) This is like bringing your new stereo home, and cranking it to it's absolute maximum volume and then complaining that you can hear hum.

From the tests I've done, one of the big differences between the GH4 mic preamps and the GH3 mic preamps, is that Panasonic added 25+ dB gain to the audio circuitry. This is why I recommend feeding a GH3 a -20 dB audio signal for best results ( set your Rode Video Mic Pro to the +20 dB setting ), but with the GH4 you should be using proper MIC ( -50 dB ) level audio signals. ( set your Rode Video Mic Pro to 0 dB )

When I first heard about this audio buzz issue I was a bit worried about the audio quality of the GH4, but the more I hear about it, I am becoming convinced this is people listening to the actual noise-floor of the camera, which is something that would NEVER happen if you have all your audio ducks in a row.

If you don't believe me, try performing the test I described above in a previous post. This test calibrates the cameras audio preamps, so you have 12 dB of digital headroom beyond the -12 test-tone level, and everything down to -63 dB RMS will be clear as a bell. This provides you with an audio dynamic range of 63 dB, which is more than sufficient if you are careful how you record your audio. Going dual-system and using a portable recorder like the ones I listed previously will buy you another 12-18 dB of clean dynamic range. For example I have started using a Fostex DC-R302 recorder with my GHx cameras, where the Fostex unit is my main recorder ( with a noise-floor of -80 dB RMS ) and I simultaneously feed the tape-out from the Fostex to my GH3 ( with the GH3 audio level set to 1 ), so I have the higher quality Fostex recording and the still very good GH3 recording. When I switch to a GH4 ( later this summer, first purchase is the Panasonic PX270 camera ), I will use the MIC out from the Fostex unit as the tape-out is way too strong for the GH4 preamps.

 

[Sol M.]

So you're saying that a fluttering that changes as the shutter speed changes is normal?

 

[HDWarrior]

It sounds like you have a Harley Davidson inside your GH4... I must admit still nothing to report of this nature on my GH4. What mic are you using ? Please remember non phantom powered mics can cause a buzzing. I have the official GH4 gun mic DWM-MS2 for external sound only, this is used as a fancy effects mic and to sync speech from my second GH2 which will eventually have a YAGH attached.

 

[TheTrickster]

I've plugged in a Mono 3.5mm cheapy mic, its got TS 3.5mm plug on it.

I (obviously) only get the Mic audio in one channel on the GH4 (Left) and listening with Stereo headphones, I can clearly hear the Microphone in the left ear - with NO Tapping / Buzzing - but the Right channel has no audio (again obviously) - but does have the Tapping / Buzzing.

Do we know the PIN out of the DWM-MS2 ? Perhaps they are doing some strange with the TRRS Pin out for the ground or something?

 

[RedBlack999]

So looks like at the moment:


Panasonic mic = clean
Any other mic = buzz


For guaranteed clean audio use a Panasonic DWM-MS2

 

[Phil_D]

Hi

These types of devices are very noisy electrically as they will have many DC-DC converters within them, and as you change settings these converters ramp up or down the frequency at which they operate. It is quite likely an external mic and wires are becoming an aerial and feeding back into the audio circuitry this noise. Perhaps recording the noise and then moving the microphone and wire around will show this changing the noise volume as the wires pick up more or less interference.

Essentially I suspect the DWM-MS2 mic has been very well screened by Panasonic to work well with this camera.

I don't expect this is a bug that will be fixed by firmware, it probably can only be fixed by changing the hardware, for example adding extra screening in the camera where the interference is escaping from, and given how full these cameras are it may not be possible to fix at all.

Regards

Phil

 

[TheTrickster]

Need someone who has the DWM-MS2 to a) confirm that yes there is no noise with that Microphone - and b) to confirm using the same camera and a different Mic, they do get the noise.

If it transpires that indeed the DWM-MS2 has some internal circuitry for dealing with this noise, we need to find an inline filter of some kind to replicate it

 

[TheDingo]

So you're saying that a fluttering that changes as the shutter speed changes is normal?

What I'm saying is that every audio recording device has a noise-floor, which is the device's true amount of audio dynamic range in dB. This is the audio range from the loudest to the quietest sounds that the device can record accurately, with no self-noise.

The Panasonic GH3 and GH4 ( and my HMC-150 ENG camera ) all have a noise-floor of approximately -63 dB RMS, so the quietest sound they can record accurately without any noise is -63 dB RMS. So from 0 dB to -63 dB RMS we have clean, accurate audio, with no noise at all.

Once you go beyond the -63 dB RMS threshold with these cameras, then you are hearing the camera's own self-noise, the noise of it's own electronic circuitry.

With the GH4 camera it appears that the camera's exposure controls can modify this noise-floor sound, so that you are hearing that crazy motorcycle like stutter when you have boosted the audio so much that you are clearly hearing the camera's own noise-floor. If you applied the same amount of audio gain to the GH3 ( or my HMC-150 ) you would not hear this odd motorcycle sound, but you would hear the horrible loud white-noise hiss of the camera's own noise-floor.

I suspect it is the additional audio gain that Panasonic gave to the GH4 audio circuits ( which is definitely a very good thing ) that has induced this modulation of the GH4's noise-floor. In other words, the extra 20-25 dB of audio gain in the GH4 is modulating the white-noise audio of the camera's noise-floor.

If you calibrate your audio levels when recording, something you should always try to do when possible, you should NEVER hear the camera's noise-floor unless you boost the audio levels too much in post. To calibrate your camera audio levels you need a device that can emit a 1 kHz test-tone, so that you can adjust the audio levels of the camera to the right amount of gain. The Fostex DC-R302 mixer/recorder device I've started using with my GHx cameras has a built-in 1 kHz test-tone, there are also a couple of fairly low-cost methods of generating a 1 kHz test if you don't own a mixer that has this feature. One is the TonePlug from Tangible Technology, which is what I used to use before I bought a mixer. The TonePlug costs about $50 and requires phantom power to operate. Another is the $30 Behringer CT100 Cable Tester which has a 1 kHz test-tone generator that runs on it's own 9-volt battery. The CT100 can be used with XLR, 1/4 inch, and 3.5mm audio connections, so it can be used without almost any audio device, and it also tests the integrity of you audio cables.

If you can't use a 1 kHz test-tone, then you can simply record some audio tests, and check to see where the audio levels of your recordings are sitting on the dB scale using your NLE. Eventually you will find some settings that will give you clean audio that sounds good, without any noise. This will normally mean NOT boosting your GH4 audio levels in post by more than 10 dB or you will start to hear the noise-floor of the camera. ( this is true for any low-cost audio device, though portable recorders have an additional 10-20 dB that their audio can be boosted without hearing their noise-floors )

Lastly, you should spend some time getting to know the features of your audio editor, as manually adjusting audio levels is always going to be much better than using the "normalize" feature. I used "normalize" all the time when I knew nothing about audio, but have since learned much better ways of doing this. The main audio features I would focus on are:

- How to manually boost or cut audio levels x number of dB ( i.e. 3, 6, 9, 12 dB )
- How to use an audio compressor ( most audio editors have this )
- How to use paragraphic EQ ( most audio editors have this )
- How to use the noise-reduction features ( most of the better audio editors have this, including the $19 GoldWave editor that I still use sometimes )

 

[Jon Nelson]

Would this work? It looks like it has the same connector as the GH4 shotgun mic...

http://www.bhphotovideo.com/bnh/con...L_q_qvin74CFc5ffgod_gkASA&Q=&is=REG&A=details

I don't think so. It doesn't state that it has DC Blocking Capacitors. The GH4 outputs voltage for powered microphones (and don't confuse this with phantom power). If you don't deal with this output voltage (block it), your audio will likely buzz because the device you are plugging into the mic jack is shorting out the output voltage.

Buzz is the least of the worries. What about the possible damage by shorting out the camera's output voltage power supply. You wouldn't plug in a "shorted" coffee pot into your kitchen counter receptacle without expecting a "buzz" when you touched the pot to pour...

 

[wwjd]

got my camera last tuesday, I don't think I have this same problem. rode mono video mic or built ins, I notice the hissy noise floor first, and some digital action buried down there, but nothing I consider unuseable or interfering. The hiss is louder than the buzzing. I can hear it in the recording of the rode mic more than the built in's but I think that is because the rode is quieter. i've heard this kind of background digital sizzle in a lot of gear, so low it is just part of the noise floor and it doesn't bother me. I would like all hiss to be gone too, but doubt that will ever happen

So, sounds like it might not be in everyone's, which is a good thing.

Testing: R0DE VideoMic (mono), Senn HD280pro headphones, Sony MDR7506, headphone volume at middle and full, rec volume +6, 0 -6, -12, monitoring direct and recorded, limiter on and off, wind noise cut "off"

k, I went back and listened to somebody's WAV back there, no, I got nothing like that ticking or flapping sound going on louder than the noise floor

 

[TheDingo]

I would like all hiss to be gone too, but doubt that will ever happen

Can you record something with your Rode Video Mic set to the 0 dB setting ( standard "normal" setting ) and your GH4 set to -12 dB, and then send a link to download this sample. ( either privately or publicly )

I'll give you my opinion on what it sounds like to me, and I'll send you a finished version of the sample using my standard workflow for audio.

You should be able to get quite good sound from the Rode Video Mic, with little hiss. ( assuming that you record in a quiet place )

 

[Ed Kishel]

So, sounds like it might not be in everyone's, which is a good thing.

That's not a good thing. Having it not be in anyone's is a good thing.


Got mine yesterday and the issue is present as well. It's mild actually, but it is there- and I don't have to struggle that badly to hear it. Two minutes out of the box and with the default mic and headphone level settings- I heard it right away. I had a beachtek dxa-2sr xlr pre-amp/adapter hooked up to it with no microphones attached and the pots turned to 0. It's there and it's not noise floor (the white noise sound that I hear in the other 5 cameras I own). It is mixed in with the noise floor. I also tried pulling the beachtek and instead using the 1k tone generator on my Shure m367 mixer (again no mics attached and all pots turned to 0) to set unity gain, and it's still there- and gets recorded.

Just using the internal mics alone, you can hear it. Although it's the most mild here, you can catch it by covering the mic holes (next to the hot shoe) with your fingers. If you only used the internal mics, I doubt you would ever hear it underneath the scene's nat sound.

If you set the gh4 mic levels to -12 (bypassing its preamps as best as possible) and you have a really strong level out from a quality mixer- it's basically real-world workable IMO. For many this is not a deal breaker. But I know it will always bother me that my $199 canon hf-r300's 3.5mm mic input sounds cleaner than my new $1700 camera's does. I'm not expecting broadcast quality mic components in a consumer model- but workable doesn't cut it for me, especially considering the gh3 didn't have this same issue. I know that during those quiet pauses from an interviewee- where I would normally expect to hear some hiss, I'm gonna hear hiss now with a light buzzing.

I'm sure the YAGH will solve the issue as it bypasses the 3.5mm jack- but I don't need this expensive, externally powered brick just for clean audio. It's going back Monday morning. If Panasonic fixes it in future production runs, great I'll re-order. I can accept white noise in my noise floor, but not white noise AND a buzzing/tapping. So for now, the gh4 is a competent stills camera, with class leading video features, but with only marginally acceptable audio quality IMO.

 

[TheDingo]

I had a beachtek dxa-2sr xlr pre-amp/adapter hooked up to it with no microphones attached and the pots turned to 0. It's there and it's not noise floor (the white noise sound that I hear in the other 5 cameras I own)

So when you bring the video into your editor, what dB levels are you seeing in your NLE when you record at the GH4 -12 setting with no microphone attached ?

I'm seeing the SAME -63 dB RMS noise-floor ( measured with the Sony Vegas Pro audio level meters ) that I see with my GH3 camera, which means that nothing is louder than the noise-floor, so the effect can't be heard without boosting the audio levels in post.

Can you post a quick video test file straight from the camera ( GH4 audio level set to -12 dB ) with no processing? I would like to investigate the audio your camera is recording.

 

[KMA_WWC]

One thing though. I still think panasonic should address/fix the buzzing while monitoring the audio whether it's being recorded to the file or not. It is still a huge issue for people who monitor from the camera jack and it's unacceptable to just leave it without any fix.

Just my 2cents