Can I record stereo sound with a parabolic reflector?

[Tokend]

Hi,

This topic isn't really Hi-MD-specific, but I've hung out here long enough to come to appreciate the expertise, spirit, and helpfulness of the forum's inhabitants. I hope this is OK.

I would like to record high quality stereo sounds at a distance. I'm looking to get an RH10 and record nature sounds and such.

I would like to rig a parabolic dish from Edmonds Scientific with a cigar-shaped stereo mic and attach it at the focal point of the dish. The thing is, I don't know if this will work.

The side-to-side distance between left and right sources would be small, because the dish would be pointed at a small area. Still, I'd love to record, say, a "conversation" between two birds on a branch and preserve the left-right orientation, if I could.

It seems like the sound waves entering the right side of the dish would get focused to the right side of the focal circle (assuming not a true point), and similarly for the waves on the left side.

But, it could also be that small inaccuracies in the dish would steer some of the left waves to the right side, and vice versa. This would make for jumbled sound.

If this is true, then would it work to put an acoustically reflective partition (say, aluminum) in the dish, effectively dividing it into two halves, left and right? This wouldn't necessarily steer errant waves to the proper side of the mic, but it would at least keep them from entering the wrong side of the mic, I would think.

I'm guessing here, as you can tell. Thanks for any thoughts,

Tokend

[atrain]

moved to the live recording section

[kypfer]

No, it won't work at a distance simply because there's no effective channel seperation at the point the microphone is located. All the sounds received at the dish will be received over the whole surface of the dish, so a "blade" down the middle of the dish will have no effect.

You may have some success with two mono "rifle" mikes, individually aimed at the sound sources, assuming the sound sources are sufficiently far apart for the mikes to be able to differentiate them.

It's all down to the effective angle of acceptance of the individual mikes and the angle between the two sources.

[AllanH]

Hi

Sorry to be contradictory, but the answer is a definite YES.

I frequently use a 'stereo parabola', and it's a commonplace set-up for wildlife sound recording.

For a complete ready to use rig look at a Telinga Pro V here: http://user.bahnhof.se/~telinga

There is a 'white paper' on this site which explains how/why the system works.

Alternatively, you can buy a parabola and use your own mics, separated by a piece of card between them. One maker of dishes is given on this site:

http://www.wildlife-sound.org/index.html

(look for the 'Amberwood Reflector' in the Equipment Section - it's bespoke made-to-order UK equipment.

You may be able to get a second-hand dish - look for an 'Atherstone Mk 3' reflector. They sometimes come up on EBay UK or on this site:

http://www.bblist.co.uk

Mics used in reflector can be electrets or condensors. I have used both. You can get reasonable results from a pair of budget lavalier omnis, but the quieter the mic the better. You need to get the mics at the focal point of the dish. You can do this by measurement if the know the focal length, or alternatively move the mics until you find the 'sweet spot'. Probably best not to use an aluminium dish or separator unless you can 'dampen it' in some way - it has a reputation for 'ringing'. Use a piece of plastic modelling card , or (literally) a postcard.

Good luck.

AllanH

Edited March 2, 2006 by AllanH

[Tokend]

kypfer & AllanH,

Thanks so much for your replies. Let's see: one thumbs up, one thumbs down. Sounds like there's only one way to find out...

If I can perhaps play mediator, the following from the cited white paper seems to indicate that you two are both right:

"The focused sound will be recorded mono, while the environment will split into a left and a right channel!"

This is great. This is perfect. If I read this right, it means that the tree full of red-winged blackbirds will be recorded as coming from everywhere (i.e., mono), while the loons to the left and geese to the right will stay where they are. Perfect.

I'll be sure to post results when and if I get around to this. Sounds like a fun project.

Thanks again for your help.

[ozpeter]

Based more on instinct than experience, I wonder whether recording with a normal stereo mic and mixing in a mono parabolic mic would work? You could thereby decide on how much focus you wanted on the distant source.

[AllanH]

Hello again

If you point the dish accurately, you will get the subject bird dead centre (ie equal output left and right giving a central image, rather than sound from everywhere), with other birds nearby distinctly off-centre, and directional background. Because the parabola gives acoustic amplification you will get a much better signal/noise ratio for a given output level than without the parabola, making it possible to get recording from a distance without scaring off the subjects. However, parabolas 'colour' the sound, being less responsive at low frequencies (but you'll know this from the Telinga pages).

It is surprisingly difficult to hold a parabola accurately for a long period without picking up handling noise or drifting off target. Telingas are better than most because they are lightweight. It's common to set up a parabola on a tripod to get around this.

Ozpeter's suggestion will work too, but you'll need a 4 track recorder or 2x MD running at the same time, unless you mix down while recording (an SQN would do nicely). Theoretically, 2 independent machines could go out of sync and produce audible phase errors as they do so but I've done a few tests and found two HiMD recorders (NH 900) keep time within a millisecond or so over a period of 20 minutes, so short recordings should be OK.

For more about nature recording try a look at the Yahoo 'naturerecordists' group.

Edited March 3, 2006 by AllanH

[sicalis]

Hello AllanH:

I see you know the SONY Hi-MD MZ-NH900. Do you know if the new model MZ-RH1 has advantages in order to record birds at field? And consider you that the TELINGA parabolic microphone are useful for these recorders?

I am trying to decide the purchase of an equipment for these purposes. Thank you in advance for your opinion.

Regards,

sicalis

[Strungup]

Hello again

If you point the dish accurately, you will get the subject bird dead centre (ie equal output left and right giving a central image, rather than sound from everywhere), with other birds nearby distinctly off-centre, and directional background. Because the parabola gives acoustic amplification you will get a much better signal/noise ratio for a given output level than without the parabola, making it possible to get recording from a distance without scaring off the subjects. However, parabolas 'colour' the sound, being less responsive at low frequencies (but you'll know this from the Telinga pages).

It is surprisingly difficult to hold a parabola accurately for a long period without picking up handling noise or drifting off target. Telingas are better than most because they are lightweight. It's common to set up a parabola on a tripod to get around this.

Ozpeter's suggestion will work too, but you'll need a 4 track recorder or 2x MD running at the same time, unless you mix down while recording (an SQN would do nicely). Theoretically, 2 independent machines could go out of sync and produce audible phase errors as they do so but I've done a few tests and found two HiMD recorders (NH 900) keep time within a millisecond or so over a period of 20 minutes, so short recordings should be OK.

For more about nature recording try a look at the Yahoo 'naturerecordists' group.

A Small Battery powered mixer and three small mics , 1 in the dish , two outside the dish, in a Y configuration everything on a Bar mount spread out 18 inches , and mounted on a Tripod or pistol grip . Thereby you have gain control and balance control to give you not only a great stereo image , but the Object or focal point can be brought clearly into focus and blended properly with the stereo field, everything mixes down to 1 recorder in stereo.

Rolls has such mixers , as well as Radio Design Labs Inc.

here is one .... http://www.rolls.com/products/mx54.php

and another..... http://www.rolls.com/products/mx124.php

and another.... http://www.rolls.com/products/mx422.php

all very nice field mixers that run on Battery , have phantom power , etc

[AllanH]

Hi folks

Any HiMD unit with a mic input will do. I've used NH-900, RH-10, RH-1. RH-10 and RH-1 are easier to use in the dark, and the RH-1 can drop straight into manual record mode with fiddly menus. No practical difference between them in terms of sonic performance that I've been able to hear.

HOWEVER - if I were starting recording now and buying new equipment, I'd be looking very closely at the new Fostex FR2LE. (Sorry to MD fans)

A Telinga rig will do perfectly - its what they're made for. Telingas have the advantage of being light and easily portable, which makes them very popular with wildlife recordists. However, all parabolas have an achilles heel when hand-held: its very easy to pick up handling noises. Although using a tripod slows down field use, its a good idea to use one if you want the best possible recording.

The idea of mutiple mics on a bar, and a parabola, and a mixer sounds interesting but might be unwieldy in the field. I have enough trouble with a lightwieght parabola on a tripod as it is. Another practical way of getting stereo is to use a mid-side rig. Put a cardioid mic at the focal point of the parabola (Sennheiser MKH40, say) and directly underneath it mount a figure-of-8 mic (MKH30), with the capsule just at the edge of the dish. The cardioid mid mic picks up directional sound from the dish; the figure-of-8 side mic picks up side-to-side ambient sound. Mix the 2 to give XY stereo. By varying the proportion of side in the mix, the width of the stereo can be manipulated after the recording has been made. This is a popular rig with wildlife recordists in the UK

Have fun.

[A440]

HOWEVER - if I were starting recording now and buying new equipment, I'd be looking very closely at the new Fostex FR2LE.

Whoa, look at the size of that thing! Not exactly stealthy. What do they have inside there, lunch?

http://www.gearwire.com/media/fostexfr2le.mov

[Strungup]

Whoa, look at the size of that thing! Not exactly stealthy. What do they have inside there, lunch?

http://www.gearwire.com/media/fostexfr2le.mov

You hear him say at the last "With a Standard 256k(and he SAY "K") card you get about an hour and a half"

so it must have multple recording formats Because PCM on a 256 would be about 15 seconds

I think he meant Meg .... still 256 megs would be about 20 minutes at PCM

Edited May 24, 2007 by Guitarfxr

[AllanH]

Erm - stealthy? with a 2ft diameter parabola?

Edited May 27, 2007 by AllanH