EX3 Audio Question

[Jay Gladwell]

Originally Posted by Brian Cassar

So, excuse me if I'm going to ask a stupid question - but does this mean that even in run n gun situations one should NOT use automatic levels?

That's right, Brian. Using the auto levels will cause more problems than they solve. It does to the sound what auto exposure does to the picture.

[Bill Davis]

Alistair's explanation is a fabulous starting point and covers most of the essentials particular to HOW to use the trim control to pad a signal presented to the microphone input on your camera. But there's a little more as to the WHY this is so critical.

Essentially, you want the signal hitting the input stage at the camera to be optimal. If it is, you shouldn't have to mess with the TRIM control at all since I'd assume the one on the EX-1 is a PASSIVE pad - suitable for lowering the signal without any capacity for actively boosting a weak signal. (Trim controls on active devices like desktop audio mixers often allow both cut and boost)

The critical factor is that strong peaks presented to any digital audio recording system are CATASTROPHIC if they result in a too hot signal entering a digital recording stage. You go from clear audio to unlistenable GARBAGE in a millisecond.

So a trim control present at the point of audio input at your camera is the FINAL line of defense between you and audio disaster.

If you'd like to learn more. Do a web search on the term "gain structure." This is the term audio engineers used to describe balancing all the inputs and output levels in a recording chain so that when the signal gets to the point you're going to record it, you've maximized the useful information in the signal WITHOUT overdriving or underdriving any particular stage and therefore adding either noise or distortion into your audio signals.

The traditional way to set gain structure allows you to use your on camera recording controls to make SAFE adjustments to your audio levels without the need to worry that you can turn things up TOO FAR and therefore spoil your recording.

In a concert or commercial recording setting, it's typical for the house to send out a 0db tone at 1Khz that you can use as a reliable baseline to set the gain structure of your camera.

WIth that, the typical procedure is to START with your on-camera audio level inputs at 80-90% of it's FULL ON setting, then use the TRIM control to set a level with enough headroom to make sure that if something BUMPS your audio control to full, you STILL have a safe level.

One sure sign of a BAD gain structure is if you're running your camera audio controls TOO LOW as a way to compensate for a hot input level. It's dangerous because if something bumps your input setting, bad things can happen fast.

Learning to consider an appropriate gain structure EVERY TIME you record sound is something on par with taking a white balance when light conditions change. Time spent working with your microphone(s), your wireless transmitters and receivers or whatever else is typically feeding you sound - and knowing how they affect your gain structure right up to the input of your camera is critical if you want to maximize your audio quality. Do that and you should rarely have to mess with the trim controls - and only when you've got not time to mess with things and someone sends you a too hot signal you aren't expecting.

Hope that helps.

[Jay Gladwell]

Thank you, Brian, for that detailed explanation.

I did a search, as you suggested, for "gain control." Again, the information provided is written by one who knows the technology for those who know and understand what the author is talking about. That leaves the rest of us out in the cold.

For instance, Sony didn't say in the manual (EX3) that the camera has Interval Recording and leave it at that. They provided detailed information (on page 74) explaining how to set up the Interval Recording capability. They should have provided similar information on how to set the Trim control.

[Dave Morrison]

Originally Posted by Jay Gladwell

Thank you, Brian, for that detailed explanation.

I did a search, as you suggested, for "gain control." Again, the information provided is written by one who knows the technology for those who know and understand what the author is talking about. That leaves the rest of us out in the cold.

For instance, Sony didn't say in the manual (EX3) that the camera has Interval Recording and leave it at that. They provided detailed information (on page 74) explaining how to set up the Interval Recording capability. They should have provided similar information on how to set the Trim control.

They did, Jay. I own the EX1 but I downloaded the EX3 manual (.pdf) and it is explained VERY briefly on Page 68 under the heading "To Adjust the Levels Manually". As others explained, you are using the initial menu-driven level controls to compensate for the different efficiencies of different brands and types of mics. If I'm standing in front of the same sound source, my condenser shotgun has a different output level than one of my handheld dynamic mics. Once I compensate for the difference between different mics (with my external faders controls set to "5"), I can then make minute adjustments once I'm rolling. And, according to the EX3 manual, this external fader can either boost your signal by +12dB (when set to "10") or cut the audio to completely off (when set to "0"). Hope that helps.

[Jay Gladwell]

Sorry, Dave, but you're mistaken. On page 68 of the manual that came with the EX3, there is nothing there as you described. And so far as the PDF copy is concerned, there's nothing on page 68 there pertaining to the use of the Trim settings, either. The below image is a screen shot taken directly from the PDF of the EX 3 Owners Manual, page 68:

[Dave Morrison]

Okay, then I must be confused as to what the question was. Can you restate it or clarify?

[Bill Davis]

Originally Posted by Jay Gladwell

Thank you, Brian, for that detailed explanation.

I did a search, as you suggested, for "gain control." Again, the information provided is written by one who knows the technology for those who know and understand what the author is talking about. That leaves the rest of us out in the cold.

For instance, Sony didn't say in the manual (EX3) that the camera has Interval Recording and leave it at that. They provided detailed information (on page 74) explaining how to set up the Interval Recording capability. They should have provided similar information on how to set the Trim control.

I'm not sure if you're responding to Brian, or me, Bill - but regardless, if you actually searched on "gain control" you're looking at a topic that's NOT the same as what I suggested which is "gain structure."

Precise terminology in this stuff matters - often quite a lot.

"gain control" would be expected to deal with controlling the amplitude of a specific audio signal hitting a specific circuit. The other - "gain structure" - deals with the process of setting appropriate gain levels throughout an entire recording chain - whether those signals are generated by a single mic or a whole passel of inputs running through a large mixer. In fact, it's in the realm of complex mixing consoles that gain structure is MOST critical, since the very tool implies adding multiple sounds and mixing them down into an appropriate master output level. But the lessons you can learn on how to set the gain structure of a large mixer - particularly setting the trim correctly and optimizing each signal in it's individual channel strip - is precisely the central skill required to properly set the gain structure of a single channel of a mic feeding your camcorder.

Properly trimmed, a signal hitting your camcorder will allow you to use that camcorder's volume control to USEFULLY limit the chance of the signal falling apart prior to being written to tape or disc.

Again, I'd do a careful search on "gain structure" and you should get a lot of useful information on how to set levels at each stage of an audio recording chain, whether that chain is a simple mic to camera mic input, or the more complex process of taking, say, a house audio feed, running it through a camera side sub-mixer - and then into your camera.

[Jay Gladwell]

Originally Posted by Dave Morrison

Okay, then I must be confused as to what the question was. Can you restate it or clarify?

I stated it as clearly as I know how in my first post in this thread. We're talking about the "Trim" settings.

[Jay Gladwell]

Originally Posted by Bill Davis

I'm not sure if you're responding to Brian, or me, Bill -

My apologies, Bill. I was replying to you. I was mistaken in my reply, too. I did a search on "gain structure" (why I typed "control" only heaven knows). How can I be sure? Because the same articles came up in the search as the other day.

Like I said, I am not a "audio" person, per se. The articles I read presumes the reader is at the same level of expertise as the writer.

All I'm searching is a simple, straight forward, non-technical explanation of the Trim settings and how to apply them. At this point, based on what has been posted in this thread so far, I am able to set the Trim with some degree of accuracy.

My second point is Sony should have provided an explantion in the manual on applying the Trim settings. They didn't.

[Bill Davis]

Originally Posted by Jay Gladwell

SNIP

All I'm searching is a simple, straight forward, non-technical explanation of the Trim settings and how to apply them. At this point, based on what has been posted in this thread so far, I am able to set the Trim with some degree of accuracy.

My second point is Sony should have provided an explantion in the manual on applying the Trim settings. They didn't.

As to the first, consider this.

A "trim" control essentially determines the RANGE that a volume control will adjust. It does so by limiting (or boosting, if an amplifying stage is involved) the level of the signal that is subsequently "seen" by that volume control.

The proper process of setting a good gain structure is to typically FIRST set the volume control a modest amount below the upper range of it's pass through capability - THEN to TRIM the signal presented to that volume control, such that when the volume control is pushed toward it's maximum, the signal stays within an optimum range of signal strength.

(If you look at analog mixing boards you'll often see a graphic indicator on the mixer's faceplate 70-80% or so down from the top of the sliders where the sliders pass optimal audio. At or near the top of this "sweet spot" range is where those volume sliders are typically set prior to adjusting the GAIN into that channel strip)

As to your second point. Welcome to how Video manuals typically discuss audio issues. Which is to say barely, if at all.

Hope this helps.

[Greg Chisholm]

The Basics Of Setting Gain Structure

http://www.soundonsound.com/sos/apr9...structure.html

if i am violating the code of ethics for dvinfo honcho's i apologize... i am just trying to help and the suggestion of searching "gain structure" yielded this informative article.


Please don't banish me... but do tell me if i am in error.?

Greg

[Mitchell Lewis]

The trims help put the level control "with in range" for the given input source (microphone, line level from a mixer, etc...)

If you look on any mixing board, there is a fader (level control) at the bottom of the channel strip and a "trim" knob at the top. This is used exactly the same way as you guys are describing on the EX3. (just thought you'd want to know)

[Bob Grant]

Mitchell has it nailed. In general cameras use voltage controlled amplifiers so the trim control is controlling gain, not level like a traditional fader would. From my experience with the EX1 getting the trim setting correct is rather critical. If you find you're setting the level controls low to avoid clipping as indicated on the meters you can still get distorted audio but it only affects low frequencies.
Apparently the last firmware upgrade changed something in the way the EX1 handles audio. I'm yet to test to see if it has addressed the issues I've noticed before the upgrade.

[Jay Gladwell]

Greg, those are excellent articles (and I appreciate you're sharing them), but, unfortunately, they still do not answer my original question.