Microphones - Sensitivity??

[taz0x]

Well i've recently started to look for very cheap, affordable shotgun microphones under $100 CDN since you know i don't have much money. I've asked an audio student about microphones, and i've learned quite a bit, and the thing that's bothering me the most is sensitivity.

i understand the sensitivity indicates how loud or how quiet the device can record at, but every microphone i see has this weird describing sensitivity, such as:

-Sensitivity: -40dB @1kHz (1V/Pa)
-Open Circuit Sensitivity: -50 dB (3.1 mV) re 1V at 1 Pa
-Open Circuit Sensitivity: Normal: -56 dB Tele: -45 dB

Like the audio student i spoke with said "i don't know why it's displayed as negative numbers"

and when i look at a Sennheiser ME66 mic the sensitivity is displayed as a positive number.

So what's better here? the less the number the better it is?? or the exact opposite?

also, if i wanted to film with subtle sounds like scratching a clipboard or like uhhh, scratching heads, how low of a frequency do i need to look for in a microphone?

and if it helps, i'm basically looking a microphone that:

-can plug in directly to a 3.5mm mic jack on my dv camera
-can film dialogue and sound effects of the surroundings in a clear as possible quality
-can block out wind and other unwanted noises
-is cheap and that will last something like a year or 2

so umm, thanks in advanced. and i'm new here so yeah nice to meet you all.

 

[M1Fanatic]

It is displayed as negative numbers because microphone output is less than 1 volt.

 

[Shadow_7]

The lower the number the softer the sound it can pick up? I'm not sure why you care about that number though? Unless you have a lot of quiet percussive type sounds you're trying to capture. Harpsicord?

Noise floor is more critical IMO as it doesn't matter how soft the sound you're picking up is if you can't hear it over the noise of the microphone. I use SPL(how loud can you go) as a determining factor, since if it can't handle a certain SPL, it's of no use for my use specific application. All other specs need not apply. You can manage some of that with mic placement and stuff. But I do more event audience perspective stuff and have little to no control over the content or location of capture.

 

[mshilarious]

i understand the sensitivity indicates how loud or how quiet the device can record at,

No, it's a simple measure of electrical output for a given acoustic input. The acoustic input is standardized at 1 Pa (Pascal), which is equivalent to 94dBSPL. 1kHz is the standard frequency at which sensitivity is measured; you can adjust for other frequencies by consulting the microphone's frequency response curve.

-Sensitivity: -40dB @1kHz (1V/Pa)
-Open Circuit Sensitivity: -50 dB (3.1 mV) re 1V at 1 Pa
-Open Circuit Sensitivity: Normal: -56 dB Tele: -45 dB

Like the audio student i spoke with said "i don't know why it's displayed as negative numbers"

Because it's expressed in dBV, which references the output voltage to 1V:

20 * log ( 0.0031 / 1 ) = -50.17

Open circuit sensitivity means that there is no load on the microphone; in other words it is not attached to a typical preamp. For most microphones, the sensitivity under load is not much different, at least if the microphone is a standard XLR output professional type. For example, if a microphone has an output impedance of 250 ohm, and the preamp has an input impedance of 1Kohm, then the voltage will drop as follows:

20 * log ( 1000 / (1000 + 250) ) = -1.94

So you would experience a drop of about -2dB from the rated open-circuit sensitivity. As the output impedance of the mic drops, that loss gets smaller.

So what's better here? the less the number the better it is?? or the exact opposite?

also, if i wanted to film with subtle sounds like scratching a clipboard or like uhhh, scratching heads, how low of a frequency do i need to look for in a microphone?

Hotter is not necessarily better, but it can be if you have to plug into a noisy preamp (because the mic's signal will be further above the preamp's noise). On the other hand, if the mic is really hot and you want to record loud sources, then you'd possibly need to attenuate the mic signal before the preamp. Otherwise, it doesn't matter too much. It is not a quality rating in any manner.

-can plug in directly to a 3.5mm mic jack on my dv camera
-can film dialogue and sound effects of the surroundings in a clear as possible quality
-can block out wind and other unwanted noises
-is cheap and that will last something like a year or 2

Some of those requirements are exclusive. For example, shotguns can record film dialogue well, but they are designed to reject surroundings ("unwanted noises"). And they are very sensitive to wind, which is why you see them used with giant fuzzy windscreens.

 

[taz0x]

The lower the number the softer the sound it can pick up? I'm not sure why you care about that number though? Unless you have a lot of quiet percussive type sounds you're trying to capture. Harpsicord?

Noise floor is more critical IMO as it doesn't matter how soft the sound you're picking up is if you can't hear it over the noise of the microphone. I use SPL(how loud can you go) as a determining factor, since if it can't handle a certain SPL, it's of no use for my use specific application. All other specs need not apply. You can manage some of that with mic placement and stuff. But I do more event audience perspective stuff and have little to no control over the content or location of capture.

are you talking about those like noise ratings i've been seeing? like what i've heard is it the measure of how much noise it blocks out and if the numbers were from like 30 to 60dB it's pretty good. but not to sure...

No, it's a simple measure of electrical output for a given acoustic input. The acoustic input is standardized at 1 Pa (Pascal), which is equivalent to 94dBSPL. 1kHz is the standard frequency at which sensitivity is measured; you can adjust for other frequencies by consulting the microphone's frequency response curve.



Because it's expressed in dBV, which references the output voltage to 1V:

20 * log ( 0.0031 / 1 ) = -50.17

Open circuit sensitivity means that there is no load on the microphone; in other words it is not attached to a typical preamp. For most microphones, the sensitivity under load is not much different, at least if the microphone is a standard XLR output professional type. For example, if a microphone has an output impedance of 250 ohm, and the preamp has an input impedance of 1Kohm, then the voltage will drop as follows:

20 * log ( 1000 / (1000 + 250) ) = -1.94

So you would experience a drop of about -2dB from the rated open-circuit sensitivity. As the output impedance of the mic drops, that loss gets smaller.




Hotter is not necessarily better, but it can be if you have to plug into a noisy preamp (because the mic's signal will be further above the preamp's noise). On the other hand, if the mic is really hot and you want to record loud sources, then you'd possibly need to attenuate the mic signal before the preamp. Otherwise, it doesn't matter too much. It is not a quality rating in any manner.




Some of those requirements are exclusive. For example, shotguns can record film dialogue well, but they are designed to reject surroundings ("unwanted noises"). And they are very sensitive to wind, which is why you see them used with giant fuzzy windscreens.

so, to put it simply... what does sensitivity even mean? how does it affect recording quality?

and if the numbers are displayed in negative numbers because this output is supposedly less than 1V, how do i know if it is still decent quality?

like basically, i'm trying to purchase something cheap like this:

http://www.amazon.com/Technica-ATR-...8&s=musical-instruments&qid=1275057758&sr=1-5

or this:

http://www.amazon.com/Azden-High-pe...&s=musical-instruments&qid=1275057758&sr=1-20

or this:

http://cgi.ebay.com/Audio-Technica-...tem&pt=LH_DefaultDomain_0&hash=item4cef974325

basically i want to know what these numbers mean in terms of how quiet of a sound it can pick up, what range (distance) it can pick up at, how much noise it can block out.

and thank you all so much for your VERY quick replies.

 

[mshilarious]

are you talking about those like noise ratings i've been seeing? like what i've heard is it the measure of how much noise it blocks out and if the numbers were from like 30 to 60dB it's pretty good. but not to sure...

Self-noise has nothing to do with rejection of off-axis sound. You need to look at the polar response chart to determine that.

so, to put it simply... what does sensitivity even mean? how does it affect recording quality?

Sensitivity has no bearing on quality, whatsoever. In fact, no microphone specification is really a measure of quality; they are measurements of fitness for a particular use.

and if the numbers are displayed in negative numbers because this output is supposedly less than 1V, how do i know if it is still decent quality?

IT HAS NOTHING TO DO WITH QUALITY.

basically i want to know what these numbers mean in terms of how quiet of a sound it can pick up

The limitation on the quietest sound a microphone can resolve is its self-noise rating.

what range (distance) it can pick up at

Microphones don't know how far away a sound is. They all pick up near and far sounds.

how much noise it can block out.

Microphones don't block noise, they reject off-axis sounds to varying degrees, according to their polar pattern chart. But they are completely incapable of rejecting any sound that is on-axis, whether you consider such sounds as desired signal or undesired noise.

The microphones you linked are different types. For example, the ATR6250 is a cardioid stereo microphone. It is not a shotgun microphone, even if it looks like one. It isn't going to reject anything that isn't directly behind it; it's going to pick up everything in about a 270 degree field in either the left or right channel.

On the other hand, the ATR6550 is a mono shotgun mic. It will pick up directly in front of it and not much else. You would use those microphones in different situations. Both of them will be very sensitive to wind, so you'll need large windscreens--larger than supplied with the mics--for use outdoors on a windy day.

AT is very reputable manufacturer, but these are in their low end, and they haven't published full specifications (no polar pattern charts) that I can find, probably because the intended target market wouldn't comprehend them. There is no self-noise rating, but with these mics it's a safe bet that self-noise is probably high (which is bad). I would expect that either mic will improve upon the internal mics of a camera, but still be well below something like the AT897.



So, you need to decide what your primary recording need is, and buy the mic that fills that. Even basic film production is going to use a number of different mics though, no single microphone can do everything, and many situations will require more than one mic.

 

[taz0x]

So, you need to decide what your primary recording need is, and buy the mic that fills that. Even basic film production is going to use a number of different mics though, no single microphone can do everything, and many situations will require more than one mic.

so uh... what if i needed something that records primarily everything? from dialogue to like ambient sounds (of the location) and sound effects like footsteps?

I never actually clearly stated what i'm wanting to use this mic for:

basically, i'm more of a film student (technically i'm studying visual effects), and i love filming stuff and i have this crappy little miniDV cam that is like the only thing i can film with. and like all consumer cameras the built in mic isn't that great. my camera has this jack i can plug a microphone into, so what i want is a shotgun microphone (or boom mic, whatever the correct term is) that can record fairly general stuff you'd notice in film, paper crumpling, footsteps, clothing (the sound of cloth interacting with each other(?)), talking, perhaps whispering. so yeah i'm trying to find something that can record something clear, or at least BETTER than my built-in mic

by the way what is a self-noise?

so, if no microphone specs are to do with quality of the sound, then AS A BEGINNER AND SOMEONE WHO NEEDS SOMETHING BASIC, what numbers should i be paying more attention to, and what numbers are considered good and bad?

 

[mshilarious]

so uh... what if i needed something that records primarily everything? from dialogue to like ambient sounds (of the location) and sound effects like footsteps?

You're a film student? OK, how about if you have one lens to film everything? Zoom lens then, right? But I forgot to mention, you are making a 3D film. One lens gets kinda hard then, doesn't it?

If you buy a mono shotgun (shotgun is a polar pattern, not a body shape) mic, you'll be able to isolate dialogue from ambient sounds. Now you have a problem if you ever want to record ambient sounds in stereo (which I imagine you do). If you have the stereo mic, you'll be able to record at a higher quality than your camcorder mic, but it won't be able to isolate dialog very well from ambient sound. These are the limitations in choosing a single microphone.

 

[Shadow_7]

http://www.audio-technica.com/cms/wired_mics/28664cc1715de436/index.html

Audio Technica - ATR-6250

dual cardiod / stereo condenser / 70Hz-18kHz / -50dB sensitivity

Good close up

---

http://www.azdencorp.com/new/product.php?productid=93733&cat=38&page=1

Azden SMX-10

dual unidirectional / stereo electret condenser / 100Hz - 18kHz / -40dB sensitivity / 60dB S/N

Good medium far away

---

http://www.audio-technica.com/cms/wired_mics/a49c539ef22b0215/index.html

Audio Technica ATR-6550

mono cardioid | super-cardioid / single condenser / 70Hz-18kHz / -56db | -45dB sensitivity

Good medium far or far far away.

---

Not to imply good. Compare those specs or lack there of with more pro line versions.

http://www.audio-technica.com/cms/wired_mics/5bbed15003fe56a2/index.html

---

You want a dynamic range > 100dB. Even a door slam is going to be louder than that. You want a S/N > 70dB, the higher the better. The one with those specs was 60dB. There's also an A weighted spec on some mics which should be < 20dB, the lower that number the quieter the mic. Self Noise is the noise that you'll record, even if the business end was in the vacuum of space. i.e. no sound waves to record.

There's some discontinued models that are likely cheap, but not that cheap. AT-822, AT-825 and others. For $50-ish, you might like the camcorders mic better. It depends on the video device though. You gain something by disconnecting the mic from the motors of the camcorder and putting some distance in there as well. But in terms of specs, those first three are probably well matched with the one that comes with your camcorder. If you're going to go that cheap, you might as well get a radio shack special. radio shack / realistic / optimus / ???. As I make arrangements to pick up a 33-1065 (33-919a). I guess I just got tired of seeing it's ad on craigslist. Plus I could always use a sacrificial lamb in bad weather.

 

[taz0x]

You're a film student? OK, how about if you have one lens to film everything? Zoom lens then, right? But I forgot to mention, you are making a 3D film. One lens gets kinda hard then, doesn't it?

If you buy a mono shotgun (shotgun is a polar pattern, not a body shape) mic, you'll be able to isolate dialogue from ambient sounds. Now you have a problem if you ever want to record ambient sounds in stereo (which I imagine you do). If you have the stereo mic, you'll be able to record at a higher quality than your camcorder mic, but it won't be able to isolate dialog very well from ambient sound. These are the limitations in choosing a single microphone.

ok so now i'm realizing that i've probably been interpreting this incorrectly. based on what you said, does that mean now there is no microphone that can generally everything you'd require at once? or is this not possible because of the fact that my budget is super low?

the reason why i was under the impression of there being a general shotgun mic that can record generally everything fairly well is because at my school we primarily use a Seinnheiser ME66 to film, and that records generally everything we need. but i'm guessing it can do that because of the fact that it's such a high quality mic than what i'm looking at.

http://www.audio-technica.com/cms/wired_mics/28664cc1715de436/index.html

Audio Technica - ATR-6250

dual cardiod / stereo condenser / 70Hz-18kHz / -50dB sensitivity

Good close up

---

http://www.azdencorp.com/new/product.php?productid=93733&cat=38&page=1

Azden SMX-10

dual unidirectional / stereo electret condenser / 100Hz - 18kHz / -40dB sensitivity / 60dB S/N

Good medium far away

---

http://www.audio-technica.com/cms/wired_mics/a49c539ef22b0215/index.html

Audio Technica ATR-6550

mono cardioid | super-cardioid / single condenser / 70Hz-18kHz / -56db | -45dB sensitivity

Good medium far or far far away.

---

Not to imply good. Compare those specs or lack there of with more pro line versions.

http://www.audio-technica.com/cms/wired_mics/5bbed15003fe56a2/index.html

---

You want a dynamic range > 100dB. Even a door slam is going to be louder than that. You want a S/N > 70dB, the higher the better. The one with those specs was 60dB. There's also an A weighted spec on some mics which should be < 20dB, the lower that number the quieter the mic. Self Noise is the noise that you'll record, even if the business end was in the vacuum of space. i.e. no sound waves to record.

There's some discontinued models that are likely cheap, but not that cheap. AT-822, AT-825 and others. For $50-ish, you might like the camcorders mic better. It depends on the video device though. You gain something by disconnecting the mic from the motors of the camcorder and putting some distance in there as well. But in terms of specs, those first three are probably well matched with the one that comes with your camcorder. If you're going to go that cheap, you might as well get a radio shack special. radio shack / realistic / optimus / ???. As I make arrangements to pick up a 33-1065 (33-919a). I guess I just got tired of seeing it's ad on craigslist. Plus I could always use a sacrificial lamb in bad weather.

ok.... see i'm looking for these "shotgun mics" because of the fact that they can pick up noise really well compared to like a mic like this:

http://www.thesource.ca/estore/prod...ategory=Microphones&catalog=Online&tab=1#more

or a condenser mic...

 

[mshilarious]

ok so now i'm realizing that i've probably been interpreting this incorrectly. based on what you said, does that mean now there is no microphone that can generally everything you'd require at once? or is this not possible because of the fact that my budget is super low?

No, it's because you only want to buy and use one microphone, which I suppose is a function of budget. It all depends on what you want to film and what results you are expecting. But it's not because of the quality of the mics per se.

Let's say you set up a scene where two characters are talking across a busy street. I assume you want to be able to hear dialogue from both sides. That's very unnatural in real life, but this is film, not real life. If you use one shotgun, you'll get one actor just fine, the other actor not so much. You will get a minimum of street noise. If you have two shotguns, you now have one for each actor. Dialogue is great, but the street is the small amount of bleed you get into the shotguns, and shotguns can sound kinda funky off-axis.

If you have two shotguns and a stereo mic for ambience, now you can blend the street noise to taste with the dialogue. But you'd need three or four mics and a four-channel recorder that has timecode sync. That gets expensive.

If you aren't doing anything that complicated, then one mic probably works fine. You might have to hustle a bit more. For example, you'd have to record ambient sounds separately and mix them in. You'd have to do a lot of automated panning or editing if you are trying to spread two actors' dialogue in stereo. But if you are happy with a mono soundtrack (perhaps with incidental music in stereo), it will work fine.

I would still suggest that you need a stereo mic for recording ambience. So if you can stretch it, the stereo mic and the shotgun mic would be nice to have.

the reason why i was under the impression of there being a general shotgun mic that can record generally everything fairly well is because at my school we primarily use a Seinnheiser ME66 to film, and that records generally everything we need. but i'm guessing it can do that because of the fact that it's such a high quality mic than what i'm looking at.

Again, depends on what you are filming. A restaurant scene with a couple talking at a table, one shotgun works great; mix in some foley restaurant noise and canned piano music later.

ok.... see i'm looking for these "shotgun mics" because of the fact that they can pick up noise really well compared to like a mic like this:

First off, all of the mics you are looking at are condensers of various types. Mics have an "operating principle" and a "polar pattern". That vocal mic you linked is a dynamic mic (operating principle). They have low sensitivity, so low that it will cause a problem with the noise of your camera's preamp. Generally, if you want good results with a dynamic mic, you have to use a professional preamp.

It also doesn't have a shotgun polar pattern, it is cardioid, so it has limited off-axis rejection (pretty good at the rear, not so good at the sides). Technically it's possible to build a dynamic shotgun, but I don't think anybody does it.

You should avoid the term "noise" when discussing acoustic sounds; again, microphones don't know what is noise and what is desired signal. They only know what sound is incident on the front, sides, and rear of the mic, and they respond according to their polar pattern. It's up to you to aim the mic accordingly. "Noise" in microphones refers to their internal electronic noise, which every mic has to greater or lesser degrees.

Polar patterns go like this:

Omni (picks up sounds from all angles equally)
Cardioid (heart-shaped, good rejection at the rear, some but not much at the sides)
Hyper/supercardioid: between cardioid and figure-8: pretty good rejection at most off-axis angles
Figure 8: picks up front and rear, very good rejection at the sides.

Shotguns are modified hypers or supers: they start with that pattern and add an interference tube to further increase side rejection.

I would not think of a shotgun as something that only picks up "far away" sounds. The problem with far away sounds is that they are quiet by the time they get to the mic. So even with really good rejection of off-axis sounds, you still have a quiet sound that has to struggle against the internal electronic noise of the microphone. And so the goal of film production is generally to get the shotgun as close as possible to the actors while staying out of the frame.

With lenses, you'd simply use a giant telephoto, which compensates for distance with aperture. Mics can do that too, except unlike lenses, mics lose resolution as they get larger. This is because a diaphragm is a mechanical device, so larger diaphragms respond more poorly than smaller ones. So you won't see any shotgun mics with 5" diaphragms.

When nature recordists struggle against this problem, they tend to go for non-mechanical acoustic enhancements: parabolic reflectors and such. Those can cause stranger effects than a shotgun, but if you're trying to record a birdsong from 100 feet, it's all you've got.

Anyway, sorry bit of a tangent there . . .

 

[Shadow_7]

A shotgun is good for picking up a talking head in a noisy parking lot. Period. End of story. It's like the laser beam of mics. Unfortunately plenty of opportunities to miss your mark if it's not aimed just right.

Hyper cardioid is more like a flashlight

Cardioid is like a headlight

OMNI is like a campfire / lantern.

Each has their preferred use and ISSUES. I prefer OMNI as once you slop a big fat dead rat on there you don't have a clue where it's actually pointing anymore. Less risk, at the costs of picking up everything.