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Saturday, September 23 2017 @ 02:25 AM CDT

Sound and Microphones

Previous: Camera Housings - Next: Internet Connections

A live wildlife stream is great, but having sound on your video stream makes a tremendous difference to its appeal. It also can be a very “interesting” facility if you are not careful in urban areas.

Setting up microphone sound is every bit as challenging as setting up the camera in the first place. Getting the right balance of sound from the major subject and some from surrounding creatures while blocking out man-made sounds or limiting their volume is an art unto itself. You may find that you need to make or purchase a “shotgun” microphone or parabolic reflector to pinpoint the source of the sound and hide or lower the volume of distracting sounds.

On the other hand, microphones don't have to be expensive to be useful. The one pictured above cost me $1.00 at the local "dollar" store - and we've used it for many projects that have worked out just fine.


Microphones don't have to be expensive to be effective

I’ve made several shotgun microphones using inexpensive microphones glued into the end of plastic funnel (dollar store set – 4 for $1) with soda straws of different lengths set in the wide end of the funnel. The original design came from a Popular Electronics magazine from the days of my youth (some time in the 1960s if I recall) but it worked just fine. Starting with the longest straws in the center (18” straws if you can find/make them) you cut each successive straw by the same amount shorter than the previous to fill the face of the funnel. I use a 3/4” difference down to the shortest being about 3” long. Hot glue or almost anything will do the job if you don’t get the plastic straws/funnel too hot.

You can purchase parabolic dishes or make do with almost anything dish-shaped - how about a "snow saucer?". Mount the microphone facing the concave side of the dish at the point where lines perpendicular to the surface of the dish most closely converge.

Distortion

I’ve had people complain to me that the sound they get is terrible, and wonder how we get such good sound on our cameras in comparison. Strangely enough, it’s really not all that hard but it takes a bit of understanding of how to set things up and what constitutes “good” sound.

To some, good sound means being able to hear anything, even faint sounds in the background, so they crank the amplifier setting (gain) away up. Then they complain that something close to the microphone sounds terrible and when there is no sound, there is “noise” in the background.

The best way to set up a microphone is so that it picks up sound mostly from exactly where the camera is aimed. This means one of two things: the microphone is really close to the subject, or the microphone can “zoom in” on the subject area with some sort of enhancement, usually a parabolic reflector or “shotgun” microphone setup.

Then you set the gain on the microphone circuit so that the loudest sound likely (eagle squawk or bear snort or...) does not sound distorted (clipping is what this is called – the nice round wave forms of normal audio are clipped off at the maximum volume so they are square on top instead – which sounds “rough”) - then let the rest of the local sounds fall where they may. You’ll still get background sounds but you won’t likely get any audio circuit noise and maybe you won’t get your neighbours fighting with their kids either.

Many inexpensive consumer video cameras either don’t allow you to use a separate microphone, or demand that you use one of the “PC” style mics with integrated power, and that don’t take kindly to either modification or to long cables to where the sound is.

Commercial security cameras typically don’t allow for a microphone at all, or as in the case of the Axis camera, may not bring the microphone socket out to the outside of a weatherproof housing. In order to take advantage of the synchronization afforded by the built-in encoder, you’ll have to somehow modify the enclosure to allow you to get the mic lead in.

The solutions available include use of professional microphones and possibly amplifiers/mixers (not useful where power is a problem and not very weather proof) or the use of purpose-built microphones from components, all of which plug in as “line in” instead of “mic in”.

We’ve largely chosen the latter and use a microphone cartridge with built-in low-noise amplifier (www.matco.com A-230AU and built-up model A-230AU-4 or A-230AU-17 ) these require 9-12 volt power which complicates wiring but we have found that they produce superior sound signal to noise and that they are adaptable to almost any situation. The microphone itself is a short cylinder and is attached to a small circuit board. These need to be built into a weather proof housing of some sort and our typical one is a short piece of ABS pipe with end-caps drilled for the cable and microphone. The container hangs with the microphone pointing down and the body may be filled with foam to both stop wind noise (see next section) and to keep insects out. It can have a full plastic (food film or other thin sheet) cover over it to completely water-proof it if necessary but the sheet will block some sound and may introduce some frequency distortion. The output and power will run quite a distance (we have some out at close to 500 feet) on shielded 3 conductor cable. This contrasts with the typical PC microphone that should probably not be used beyond about 50’ from the PC via extension cables.

As noted above, the other microphone we’ve used a lot comes from the local “dollar” store. It is typically in a plastic “lavalier” style clip-on container but that can be removed exposing the bare microphone button. These work pretty much the same as much more expensive microphones but they are “throw away” in that it matters little if they get damaged. We’ve used them in situations where weather proofing simply was not an option as it would have made the microphone too large – so we just stuck the bare button mic, wrapped in a piece of foam, into the enclosure and left it at that. Again, putting the microphone close to the subject means you don’t have to crank the gain up to get usable sound.

There are also microphone kits such as:

MK136 - Stereo "Super Ear"

Wind noise

Another annoying aspect of sound is wind noise. This is best dealt with through placement of the microphone where the wind can’t easily get at it, but if necessary you need to create a wind screen around the mic. The professionals use “reticulated foam” covers. The “reticulated” means it is very open, low density and allows the passage of air – because of course you want the sound to pass but you need the low frequencies (wind noise) to be attenuated (dropped in relative volume). You can purchase these in various sizes (and colors) at your local music equipment store or you can make them if you have foam used in packing some types of electronics. The foam packing is usually dark gray in color and may be either stiff or in flexible sheets. Cut it, don’t melt it as that closes the foam holes. In a pinch I used a knitted wool cap, wrapped around a button microphone, as a wind sock. This lasted very well over a 5 month winter on a camera platform with one of the dollar-store mics. We’d forgotten to bring the microphone wind sock so I sacrificed my hat.

Placement

Place your microphone as close to the critter you're interested in as possible. We sometimes place a microphone right in the nesting materials of the eagles for example.

If you can't get that close then you might consider using some sort of directional microphone setup such as the "soda straw" shotgun described above.

You should also use a directional microphone in situations where humans might be around. Aim the mic to "see" the critter and so that it can't "see" the typical source of human sounds. This may mean aiming the microphone more up than down, in which case you need to consider allowing rain to flow out of the system without damaging the sound or the microphone. Holes in the "snow saucer" will not materially interfere with its ability to direct sound back toward the microphone, but will keep the saucer from filling with water.

You might also insulate the back of the microphone holder and surround to muffle sound coming from that direction.

Long Cables

The best way to deal with long cables is simply to not have any. The problem with long cables is that they drop the volume of the sound and can introduce noise by picking up things like radio stations and hum from power lines.

If you are using PC microphones you’ll quickly find out that the only practical way to lengthen the cable (it is very fine wire, hard to work with) is to use an extension cable with a socket on one end and plug on the other. I’ve used two 25’ extensions with a mic but that’s about as far as I’d ever like to go and it caused weather proofing problems as each of the two joins had to be separately wrapped. Finding good quality cables (and paying for them when you do find them) is not easy. The typical ones do not have gold contacts in the plugs/sockets (neither do most microphones) so there is good chance for corrosion at each joint in humid/wet climates. Corrosion causes distortion because the corrosion acts as a diode – allowing current flow more in one direction than in the other, which distorts the audio. This won’t be apparent when you first install it but will accumulate over time.

See the section on Overcoming Distance for some pointers on long cable runs.

Tag: sound microphone cable length distortion amplifier mixer shotgun microphone clipping

 

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