Proper Mic Placement

[John Nantz]

Personally, I look at the terms more from a physical or Physics point of view.

Echo: this would be like throwing a rock into a body of water (with no existing waves) and where the wave hits, say, a wall, and is reflected back to it's origin, that reflected wave would be an echo. On a pool/billiard table an echo would be the cue ball bouncing off something and returning back to where the cue hit it.

Reverberation: That would be when the reflected wave hits another wall but this time on the opposite side, bounces off the wall and returns. The returned wave would be the reverberation. On a pool table the cue ball would be bouncing off one bank and then another. But it would have to go past the point where it was originally (maybe more than once?) otherwise it would be just a ricochet.

Time: I don't know why there should be a time limit, whether it be seconds or what ever. If one is working in an atomic scale a wave, or particle, could travel at the speed of light. On a cosmic scale there is sunlight that bounces off the moon and goes back to the Earth, and I'm sure some percentage of it is bounced back again to the moon. Earthquakes cause tsunamis that create waves that can reverberate throughout the ocean. I don't understand why a time limit should be distinguishing factor. Surely there must be some reason behind it.

That's my 2c worth.

[Greg Miller]

John, I like your echo analogy. To my mind, an echo is a discrete reflection that the brain can perceive as such. If I yell "hello" at a cliff, and the sound returns to me with enough delay that I can hear the word "hello" again, that's an echo. If I'm standing on stage in an empty auditorium, and clap my hands, and a fraction of a second later I hear my clap bouncing off the back wall, that's an echo.

And if the stage curtains are open and the clap bounces back and forth between the rear house wall, and the upstage wall and back and forth a few times, that's a special case which I've heard referred to as a "slap echo."

Anyway, I think the issue about minimum delay (20ms, 33ms, 50ms, depending on whom you ask) is because your brain needs a certain amount of delay to perceive the reflection as a separate echo, and not just coloration of the original sound. In fact, if you make the time short enough and you create a comb filter.

Now if I'm singing in the shower, I hear a lot of first-order and multiple-order reflections of my voice. But they occur so soon in time that I don't hear them as individual echoes... I just perceive that the room is very "warm" and resonant. (In fact there's some reinforcement, and probably some destructive subtraction too, at various frequencies... related to the room dimensions and wavelength of different frequencies.) I don't think I would quite call this "reverberation" because it dies out very quickly. It's just coloration of the original sound.

But now get in a big room like a masonry cathedral, with lots of hard, reflective surfaces, and say or sing something. You might, indeed, hear a distinct echo (depending on the room and your location in it), but you will also hear a countless number of first-order and multiple-order reflections as the sound bounces around from the walls, floor, ceiling, pillars, wooden pews (if any), etc. They are so many in number and so diverse in time that you can't distinguish individual reflections... they take a while to build up to their loudest, and take longer to die away completely. That is certainly reverberation.

Interestingly, though, what used to be called an "echo chamber" really produced artificial reverberation. Oh well...

[Jon Fairhurst]

It seems to me that this is a point of view issue.

From the point of view of human perception, an echo is very different than reverberation.

From a physical world point of view, an echo is simply a reflection. For instance, for a radio signal echo from a building or mountain, the 20ms threshold is meaningless.

And when describing audio situations to a potential novice, precise language is often sacrificed in order to communicate technical concepts (reverberation) using familiar terms (echo). Unfortunately, looser language usage sometimes sticks.

Back on topic, I agree with Sabyasachi. An on-camera mic can be helpful in providing a reference track to synchronize an external recording or as a basis for ADR or other audio replacement. When not intending to use in-camera audio in the final product, I turn automatic-gain-control ON. I do this as insurance so I will get a useful reference track without monitoring, adjusting gain, or otherwise distracting from shooting the image. And yes, in some documentary situations, I've ended up using this audio when things didn't go as planned.

One place where I've used on-camera mics on purpose is at tradeshows. Yes, I've done the lav thing, but it's a hassle, it takes time and effort to hide the wire, and it can be the extra hurdle that can make somebody refuse the interview. For a tradeshow video, I'd rather get the shot with so-so audio than no shot at all. The trick is to use a wide lens (28-35mm on full frame), and to get the camera close to the subject. It's not ideal, as people aren't as attractive up close, but it keeps the crowd from walking into the interview, provides a certain intimacy to the audience, captures a wide view of the tradeshow eyecandy, and gets the on-camera mic close to the talent. Yes, it delivers an imperfect image and sound recording, but this approach with a simple monopod is fast and light for a one-man crew.

With a 3-man crew, you can add a boom and have a person hold an LED light. Those keep people from accidentally walking into the scene when the camera is at a distance. Alternately, the "audio person" can do the on-camera interview with a handheld mic. One can roll the on-camera mic if desired, but from six feet or more at a tradeshow, the audio would be worthless as a backup.

[Colin McDonald]

If I can make a serious comment for once (apologies to Garret for my earlier frivolity - I didn't think there was anything to argue about in what he said): on the subject of echo vs. reverb, I can understand from Paul's point of view as a marker in Sound Engineering examinations that the difference between echo and reverb is made clear to students, and the fault/effect demonstrated in the camera audio in question was clearly reverb and not echo - "echo" given as an answer here would be marked wrong, end of story.

I am not sure of the precise definition used by the various Examination Boards in England and Wales, but the Scottish Qualifications Authority's Sound Engineering Glossary has this to say:

reverb – The natural series of very short and dense echoes of a sound
that occur in a confined space such as a room or a hall. While echoes
with a longer delay would be discernible, in reverb the echoes
happen so fast and are so dense, it is impossible for the listener to
hear individual repeats. Reverb is the essence of natural sound.
Listening to a close miked instrument is like having the instrument
play in your ear in a very small room. The addition of reverb to a
sound makes it appear as if the instrument is being played in a real
acoustic. Nowadays reverb can be emulated digitally very easily and
nearly all effects processors have a wide range of reverb types for
different applications. See also gated reverb.

[Paul R Johnson]

Reverberation and echo are varieties of reflections, if we want to be pedantic. Echo is not a appropriate word to use to describe what we're talking about. A series of discrete echoes, would not be reverberation. As has been said, the usual key discriminator between echo and reverb is the 30ms rule - coupled with the fact that reverberation does not have clearly defined individual returns. We can detect what the audio people term as flutter when a number of closely spaced (in time) returns arrive at the ear. It's still not reverb.

I'm only interested in correct identification, and a live room, such as the one we hear in the clip contains no content identifiable as echo, as all returns are too close. All they do is colour the sound.

[Garrett Low]

Originally Posted by Colin McDonald

If I can make a serious comment for once (apologies to Garret for my earlier frivolity - I didn't think there was anything to argue about in what he said):

No need to apologies Colin. I actually found it quite amusing and would have made additional comments about the speaker's hair but I didn't want to seem irreverent about a Stanford University professor.

Originally Posted by Paul R Johnson

I'm only interested in correct identification, and a live room, such as the one we hear in the clip contains no content identifiable as echo, as all returns are too close. All they do is colour the sound.

My apologies to all regarding the use of "echo". While those who are audio specialists would not classify what they heard in the clip as echos but instead as reverberation, those of us who have studied physics and had years of energy and wave theory crammed into our somewhat limited brains would tell you that you are completely insane (please note the sarcasm in my use of words to keep the discussion light). In the world of physics you cannot, yes, absolutely cannot, have reverberation without the presence of echoes. As Jon had noted, in physics, time has no bearing on an echo or the definition of one. It is simply the reflection of a wave. In fact, there is no requirement that an echo needs to be within the audible range. It is simply the reflection of energy, in the form of a wave, off of a surface. The energy contained in the reflection must be equal to or less than that of the incidental wave. All of this discussion has caused me to go back and once again, spend needless hours looking through my old physics texts which has caused me to come to the same conclusion I did 20 some odd years ago, there are some very smart people figuring out things that have no real bearing on the majority of those living in the real world. And, as one of my old materials science professors use to say, "It just doesn't matter" (said with a very distinct English accent).

Sorry for the sidetrack. I am the easily distracted type. So, to get back to the original discussion.... and to respond to Sabyasachi's post, I agree that there are situations where getting a mic close to the source is not possible. In those instances you make do with what you can. The video was meant as a response to one of the questions I get asked a lot, "how can I improve the sound on my videos?" I usually discover that they are using a mic placed on top of their camera or the internal mic on their camera. My response is usually, "get the mic closer to the speaker."

[Paul R Johnson]

It's OK, I understand. However - none of my gizmos, and I have a lot, has a knob labelled 'echo' - we have reverbs, delays and modulation.

Coincidences abound - Myself, like Colin have been involved with education. I was Principal Examiner for Music Technology when it first arrived on the scene in the UK - so use of precise language is pretty important.

Probably things are different in the US, where language does get 'adjusted'. The misuse is pretty widespread, we even had a few proper echo units years ago, didn't we - Roland Space Echo and Watkins Copycat, with tape and drum echo, and then spring reverbs and even the EMT plate echoes, which were not echo.

Here in the UK, in electronic engineering and physics we've been using reflections since the radar days, although just to muddy the waters, people often called the blip on the screen the echo return - but I guess I can see this one.

I'll stick with reverb.

For what it's worth, the new removal plugins are actually very good, and although people generally use them on music, they might be interesting to give a boost to video work where the room is tricky?

[Sabyasachi Patra]

Hi John,
I am using a Telinga Parabolic microphone to record distant sounds. It is bulky and carrying it in the field becomes a challenge along with all the other equipment. I find that placing the parabolic microphone in a tripod gives better results else there is some handling noise. The other challenge is it catches dust due to its shape.

I am also recording directly to my camera through the Sennheiser MKH 416. I am also trying to remotely place microphones as well as take the microphone as close to the animal as possible, place it and then back off. I am getting the best sounds early in the morning or late in the evening and in night when human activity is minimal and the ambient noise is less. During those times, I am also able to increase the gain without any noticeable problem.

The dolphin story in incredibly touching. Thanks for sharing.

Cheers,
Sabyasachi

Originally Posted by John Nantz

Same here. Not only for syncing but for backup insurance. There's nothing like a little bit of redundancy because "Stuff" happens.

Animal sounds are quite unique and can't easily be replicated in post. If something happened when recording and nothing was captured on the camera you could be totally out of luck.

Have you ever used a parabolic reflector to aid capturing audio? Except for the bulkiness aspect, it seems this would be good for wildlife sounds. It's not like one can put a lavalier on them.

Speaking of wildlife recordings, there was a great video (not great from a videographers standpoint, but great from a wildlife standpoint) of a dolphin that requested help from a diver to remove some wire or line from a fishing net that was wrapped around it's fin. The divers in the boat recognized the dolphin was trying to tell them something and finally figured out it was a call for help.

Editorial Comment:
This was not only a call to help a lone dolphin, but a call to help a species, the animal kingdom, and actually, the whole environment.

A local salmon stream fish count has gone from ~125 ten years ago down to 0 last year. A large shopping center was built at it's headwaters and runoff from the development goes into the stream. Most people are totally clueless about the environment, and that includes the Poulsbo City Planning Commission and the Poulsbo Council that approved it. Ten years: From a Salmon stream to a Dead stream.

[Jon Fairhurst]

Originally Posted by Paul R Johnson

I'll stick with reverb.

My spell checkers don't recognize the term, "reverb". Not sure why. The term has been printed on guitar amps made since the '50s, so it's not exactly the latest slang. "Reverberation", and "echo" are both recognized, but until this thread, I don't know that I'd ever spelled out the word "reverberation".