Pocket 4K - weak preamps?

Interesting, I’ve found the audio capabilities of the P4K very very competent. I often use line level signals into it, but even with my Rode VideoMic Me sounds just fine. I’m not doing professional audio with that setup, but the XLR is fine stock and add a FETHEAD Phantom or Cloudlifter and you’re 100% fine for pro work dynamic mics even.

I also get disturbingly low audio levels via the 3.5mm input on my BMPCC4K and have found that it is not possible to record audio via the 3.5mm input at acceptable levels without using some sort of pre-amp.

In addition, the built-in camera mics also have very low recording levels and this source is not usable without being boosted in post.

I have tested the following audio configurations:

1) On-camera built in mics: Camera L/R input levels set to "100" with talent speaking into the mic on-axis from less than 1 meter away in a loud speaking voice does not exceed -18dB.

2) Rode VideoMicro mic (unpowered) plugged in via 3.5mm input set to L/R or MONO at mic level: Camera input levels to "100" with talent speaking into the mic on-axis from less than 1 meter away in a loud speaking voice does not exceed -18dB.

3) Rode Filmmaker Kit wireless lavalier mic via 3.5mm input set to mic, with Rode onboard pre-amp set to 0 dB, and camera input set to "100" with talent less than .5 meter away from mic using a loud speaking voice provides input levels that hover around -6dB. Increasing the onboard pre-amp of the Rode Filmmaker Kit wireless lavalier mic to +10dB or more provides more acceptable levels.

4) Mini-XLR input: Using this input with a Sennheiser MKH-416 P48 with the camera phantom power turned on provides levels that are acceptable.

In summary, it appears that use of an external pre-amp is required for audio sources plugged in via the 3.5mm input, and the built-in camera mics cannot record at acceptable levels either. A phantom powered mic connected via the mini XLR is the only way to get acceptable audio levels with this camera in my experience.

Let's hope that these audio issues get fixed with the next firmware update.

Interesting, I’ve found the audio capabilities of the P4K very very competent. I often use line level signals into it, but even with my Rode VideoMic Me sounds just fine. I’m not doing professional audio with that setup, but the XLR is fine stock and add a FETHEAD Phantom or Cloudlifter and you’re 100% fine for pro work dynamic mics even.

What mics are you using?

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I posted this in another related thread, but to inform as widely as possible, here is my inexpensive and effective solution to all the audio issues with the BMPCC4K: https://australianimage.com.au/blackmag ... -4k-pt-10/. The video at the end shows how it works.

Hi Ray,
Just circling back.. are you just plugging into your audio recorder for sound now or are you still using the Pocket's 3.5mm input?

I'm curious about this too

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For me, the last two firmware updates have largely resolved the issue.

When weak preamplification of microphones is a problem, I would first check whether your BM Pocket 4K has been updated to Firmware version 6.1 or higher.

I've been holding back on the updates because I like using DNG Raw. Is the audio really much improved post update?

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Hi - I’ve always used external mics either in the XLR or the 3.5mm mic port until yesterday when I had to use the internal mics and even at 100% gain, the meters registered nothing (I was recording an amplified talk in an auditorium). It was scratch sound so it doesn’t really matter but in testing afterwards, speaking in a louder than usual voice, less than one foot from the camera barely registered higher than -30dB. Before I contact CVP again (already sent it off once for the LCD screen) is that really just normal? Seems next to useless if so? My Fuji camera that was recording third camera also with its internal mic gives a very clear reference sound (and was twice as far away).

Hi - I’ve always used external mics either in the XLR or the 3.5mm mic port until yesterday when I had to use the internal mics and even at 100% gain, the meters registered nothing (I was recording an amplified talk in an auditorium). It was scratch sound so it doesn’t really matter but in testing afterwards, speaking in a louder than usual voice, less than one foot from the camera barely registered higher than -30dB. Before I contact CVP again (already sent it off once for the LCD screen) is that really just normal? Seems next to useless if so? My Fuji camera that was recording third camera also with its internal mic gives a very clear reference sound (and was twice as far away).

What you're reporting is pretty much the opposite of what people have been complaining about since the camera was released: the 3.5mm mic input has such low gain that it's unusable at anything but 100%, and 100% is too noisy.

The onboard mics, by contrast, get better levels, though sill low compared to cameras. So it looks like you have the reverse situation.

What you're reporting is pretty much the opposite of what people have been complaining about since the camera was released: the 3.5mm mic input has such low gain that it's unusable at anything but 100%, and 100% is too noisy.

The onboard mics, by contrast, get better levels, though sill low compared to cameras. So it looks like you have the reverse situation.

Thanks for responding - in this case I’m guessing I have a defective unit. Assuming there’s not some obvious setting I’m missing that has set the mics to -20dB or something (not that I can find anyway). Guess I’ll get in touch with CVP.

Thanks!

I'd be careful there. Lots of people thought they had defective units, but they come back exactly the same. Before you go to the trouble of a return, you might want to try to get to another unit, for comparison.

When I do my tests and I’m operating the BMPCC4K from behind the camera, with all audio set to 50% (neutral, no gain), I need to speak up, but I do get usable audio from the built-in camera mics.

Glad my MKH416 shotgun will be fine. Quite discouraging about the 3.5mm, but I’ll be hanging a Tentacle off it anyway. It’s so hard to know if these are working to spec or are defective. Grant Petty has nothing but praise for the four camera mics.


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I too have low levels with my Deity D3Pro on the 3.5mm jack, even with 10db gain.

Hey guys -
I want to plug in my Rode Videomic pro into the Mini XLR port but it has a 3.5mm.
Has anyone seen a 3.5mm -> Mini XLR cable? I've only seen 3.5mm -> XLR so would have to get another XLR -> Mini XLR cable. But, I'd really like just one cable.

Adapters are available, but this is not the best solution, as the Video Mic Pro is a HiZ unbalanced mic output, and the Pocket’s 4K XLR is a balanced LoZ +4dB input, so the signal level from the Video ic Pro will not match impedance wise, and will be lower than what the XLR requires. It may work, but using the camera’s unbalanced 1/8 TRS input will work better.
Cheers

Thanks, Denny. Did not know that.

The Rode video mic has an output impedance of 200 ohms which is normal for a microphone, it is not hiz, with the correct unbalance to balanced cable it should work into the xlr. Working unbalanced should not be a problem with such short cables.

Thanks Richard, given its interface, I had made a wrong assumption, thanks for the correction. Most of the 1/8 TRS mics I had used we’re HiZi. Yes a TRS to XLR should work fine, but again a 600 ohm, balanced high gain mic would be better. I use the Sennheiser ME Series, they work fine with the Pocket 4K.
Cheers

Thanks for the added info, guys. I'll see if I can find a cable to try the Mini XLR port.

I think most discussions about weak preamps can be explained.

If an audio signal is not very loud, it quickly becomes very difficult to capture usable audio. This applies to all audio recording technologies, be it analogue with tape or digital. This is just how it is. That's why there are Lavalier microphones close to the source, booms with enclosure around the shotgun mic, delicately placed microphones not seen from the camera, wind-shielding fur material, and vocal overdubs in the studio. In general the microphone should be as close as possible to the source, or shielded accordingly. You all know that, but in this discussion I felt it was worth repeating.

When watching movies I often wonder how they got the audio signals so perfectly recorded. This is a science by itself. It is not trivial, these audio guys know their art extremely well.

It is very important that BMD cameras (or any camera with internal microphones) do not amplify the incoming signal too much. If they did, users would complain about distorted audio, which is completely unusable. They would complain about noise. One can boost the signal in post, but then there is still the choice available to re-record in studio environment, or apply noise reduction and noise gate.

Most of us will know well that with analogue gear there is some tolerance because tape allows some over-saturation, while digital recording has no tolerance at all. When the signal is clipped, it is clipped. That's why there are very complicated and sophisticated limiting processing going on in digital recording cameras to prevent going over 0dB. But this is only a help for the (digital) cameraman, in general it is better to record at levels that have some headroom below 0dB.

Capturing good audio is a very complicated thing. Just like capturing images. One can use internal microphones, but one shouldn't expect too much. The same applies to external microphones, one slight mistake and your audio is useless. Know your enemy (the physical laws of sound transmission though a medium, and the limits of digital recording), and it will become your friend.

In the uk the broadcast spec if for a loudness level of -23db and a maximum peak of -2db. This matches the old analogue PPM quite well where dialogue is around zero level with peaks to +8. translated to the dbfs scale most dialogue is around -20 with peaks to -12. The extra digital headroom above -12 is to cope with those unexpected peaks like door slams.