What setting is causing my audio to dip?

lora-s wrote on 11/18/2017, 3:13 PM

Hi Everyone

I recently upgraded to a Sony FDR AX33 to record violin tutorials involving playing, talking, playing, talking.

I use a Rode condenser shotgun mic plugged into the mic jack, and I use Vegas Movie Studio version 14.

The camera audio seems to be on some sort of AUTOMATIC adjustment....because each time after I play my violin, when I speak, my voice is barely audible, and gradually increases back to normal in about 6-8 seconds.

I have the camera's audio record levels set to MANUAL. "My Voice Cancelling" is off, "Auto Wind NR" is off.

I fixed the problem on my old Sony (HDR-XR260) camera buy setting my audio levels to MANUAL, but I cannot figure it out on the new camera.

Any ideas?

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lora-s wrote on 11/24/2017, 3:30 PM

Hi Matthias,

THank you for digging the video up! I had actually watched the same video in my research. It's GREAT information. But it doesn't address the "auto-changes" that occur due to the built in "limiter" on the Sony FDR AX53. The built in limiter overrides any manual settings, and it causes my VOICE to dip way too low after I stop playing the violin, and it takes about 5 seconds for it to bring the levels back up. The ONLY way around this is to record audio EXTERNALLY from the camera, which I can do. Thanks again.

cris wrote on 11/25/2017, 2:24 PM

Well everyone, I found out that this problem is a limitation of the expensive camcorder I purchased. Piece of crap Sony FDR-AX33 has a built in "audio limiter" which OVER-RIDES any settings of a plug in device or any manual setting within the camera's own audio settings.

This is SUCH CRAP. So why have manual settings at all if Sony just thinks they know better than what I want do do with my audio? Why not just have a button that says, "Sony Knows Best" and remove all user settings.

My only option is to record externally, and mess with additional audio tracks.

Does anyone know by any chance how to prevent Vegas Movie Studio from compressing my external audio? It always compresses it so severely that it is useless. I can't line up the peaks to sync the camera with the audio, and soft sounds ARE NOT audible. Thoughts? I've always avoided external audio for this very reason.

Alright, there's an autolimiter.. but yours is more likely to be a rookie error than a camera problem. You see, a very fast compressor, that is, a limiter, simply kicks in when there is too much audio gain. If it didn't, you'd simply end up with a distorted ugly mess.

Now if it's a new camera, big chance is that your A/D converter outputs digital audio at 24bits. At that bit depth, your gain should never be anywhere around 0dbFS... your average should be around -18dbFS, your peaks -9dbFS.At 24bits your noise floor is so low that at these full scale levels you can post process the gain (in MS for example) and still have none - your background noise is likely to be much higher than the inherent equipment noise floor (and how to avoid that is another set of skills entirely to be acquired).

Even at 16bit, like older kit used to do, you want to stay on average around -12dbFS and peaks at -9dBFS.

So you simply have to reduce your gain, and the limiter will never need to kick in. Now it may be that your camera has a preamp gain/level setting, most preamps do (but as I make music videos, I never record with an external mic on the camera as the audio is there just for synch). It's probably the same place where you turn on phantom power. Note that you may have a "master level" (volume) control, that is not the same as the gain.. that can be used to get a louder signal at low gain if necessary. Or you do it in post.

If your camera preamp doesn't have a gain setting, you've simply bought a microphone that's too sensitive. There are a few measurements in use but what you wanna look is the sensitivity in dbV/Pascal. Don't remember what mic you had other than it was a Røde - they tend to be quite ok mics for simple things, and they are modern - so they tend to be quite sensitive (which is usually a good thing). You may want a dynamic microphone rather than a condenser, or a passive ribbon mic (even if modern ones are not so low sensitivity as older ones, because usually the problem is low sensitivity). The classic low sensitivity microphone is a SM7B, which usually requires at least 60db of gain from the preamp.

For sync purposes, make a loud percussive sound relatively near to the mic, and you should see a nice sync spike even if your preamp is set to lower gain or your mic has low sensitivity.

Don't mean no offense of course, gain structure is something most people get wrong to begin with, especially with digital kit. Hopefully it'll help.

lora-s wrote on 11/25/2017, 8:43 PM

Chris,

Thank you for this lengthy and informative reply. I am never offended when someone who knows more than I do points out something I could do differently!

Your idea about preventing the limiter from ever kicking in is an intriguing one. I will try some tests.

First a quick question: you are referring to a "preamp". In regards to my Sony camera....is this just the manual recording level?

As far as your syncing suggestion (percussive sound), that would work beautifully, but ideally I would like to avoid having to utilize separate Audio tracks in addition to everything else I am doing. Too many loose parts and pieces to keep track of. Of course, if it makes the difference between an A-grade product versus B-grade...I will obviously deal with the hassle.

THANK YOU again for sharing your expertise here. If you could just answer me about the preamp. I wanna make sure I understand.

cris wrote on 11/26/2017, 12:21 PM

No worries. A microphone is a simple device that translates air vibration into voltage differences over time (an analog "signal"). This voltage however is very small, and it needs to be pre-amplified so that it becomes much easier for the components later in the chain to work with it. That's the job of the pre-amplifier ("preamp"). All preamps have a way to regulate how much the small, microphone-level signal is amplified: this control is called "gain". The idea is in that way you can adjust the preamp to get just the output voltage you want, depending on the input level you're getting from the microphone you're using, which will be more or less depending on microphone sensitivity and other stuff.

So, if you can plug a mic in your camera, that means simply that the camera has a preamp. It'd be very unlikely not to have a gain control. Some oddball mics have a preamp built-in in the mic (USB mics for example): not sure about your Røde - there is at least one, the "Videomic pro" which have a gain control switch to regulate the level of input it's gonna give to the preamp. Which Røde is yours, btw?

I suspect your camera gain is set very high - together with a quite sensitive microphone, that would generate too high a voltage and kick the limiter/compressor into action. An alternative could be a mic like the Pro above that's set to output very high gain, and then goes into the preamp which further increases it, getting the limiter to kick in.

So that you can see the full chain: after the preamp, you may have a bunch of analog controls (volume, for example) and if your kit is emitting digital audio, you'll have an analog/digital (A/D) converter, which transforms the analog signal into a data stream, by sampling it at a frequency you like (say, 44.1 or 48KHz), with each sample consisting of a word of a certain length (say, 16 or 24 bits). Since (I guess) your camera saves audio as digital data on an card, it also has an A/D converter. This data stream is what Movie Studio reads and uses, and by default should do absolutely nothing with it. You can see if it does simply playing out the audio with some other program (say windows media player or the likes).

cris wrote on 11/26/2017, 12:28 PM

Just looked at the specs for the FDR-AX33 btw (https://www.sony.com/electronics/handycam-camcorders/fdr-ax33/specifications) and it says clearly that the "mic level control" (a consumer word for preamp gain) has 31 steps. It also, btw, outputs digital audio at 16bit (which is still fine but slightly harder to work with as gain level changes will affect the signal much more than with 24bit).

lora-s wrote on 11/28/2017, 12:36 PM

Fantastic information, Chris. Man, I have A LOT to learn. I ran some tests with mic levels (pre-amps) set lower. I will know later today if that did the trick. If it DID, then I'm done. If it did NOT do the trick, I will proceed to fuss with possibly external audio, or lowering the mic levels even more, and then adding "gain" while editing in Sony. Geez. Thanks for your significant time spent on this.

lora-s wrote on 11/28/2017, 12:43 PM

Chris, just FYI: I lowered my mic level on the FDR-AX33 six notches from the highest notch, (which is still pretty high)....and so far, my voice is not cutting out after I stop playing. Woo hoo!