Compressor pedal... in REVERSE?! For divers...

[ForrestS]

This is a strange one, so prepare yourself.

 

Let me "dive" right into this one. I work on a commercial dive boat. The divers are wearing commercial dive hats with a wired in microphone and speaker. Since a speaker and microphone are essentially the same thing they share the same two wires. These two wires then go to the dive boat where we have a "com-box". This com-box enables us to have a constant audio stream from the diver. With a push of a handheld (think CB radio) the signal goes in the opposite direction to enable topside to talk with the diver. All of this through the same two wires back down to the diver.

 

So this is what I'm after:

Because the microphone from the diver is a continuous stream we can hear him breathing the entire time. And then when the diver talks we can also hear that as well of course. However the breathing of the diver can be incredibly loud compared to the level of them talking. I had the idea of putting a compressor pedal right before the signal enters the combox to even out the decibels between the breathing and the talking. It works great until topside needs to talk to the diver. That's because the signal then flows in the opposite direction through the compressor pedal.

 

Is there any compressor pedals that will work with signal flowing in either direction?

 

Or maybe there is a better solution out there.

[WRGKMC]

I haven't looked into the details of that kind of audio system but as a tech I'd venture to guess its a 12V intercom type system. Intercoms can run through long wire runs and are bidirectional. (unless this is skin diving and they are using some kind of wireless transmitter/receiver)

 

As to a solution a compressor does not provide a solution. All you do is raise the noise floor and make the problem worse.

What you'd want is an expander that does the opposite of a compressor. Instead of making all sounds an equal volume, you want to make weak sounds like breathing quieter, and loud speaking tones louder. A primitive version of this is used on CB radios. Its called a squelch circuit. Its essentially a gate that can be adjusted to mute all sounds below a certain volume and when a louder speaking tone is made the gate opens and allows the sounds through. I know this kind of circuitry is used with underwater stuff because my uncle was a pro skin diver his entire life.

 

I'm not up to speed on what's available today but I'd only advise using gear designed and tested for this application. That man under water is risking his life when under water and communication is his only life line to the surface. If anything was to go wrong, especially when he's in an emergency situation, it could mean his death. I do not recommend connecting any devices that might impede that communication in any shape manor or form. You should seek out solutions designed and tested for that application only. If you rig something up, it fails and causes the loss of life or injury, you'd be solely responsible for it.

 

A true story along similar lines. I worked in the business equipment industry for a number of years. Copiers and printers use heaters to melt the toner on paper. The units are thermostatically controlled and have thermal fuses to remove power if the thermistors fail to regulate heat,

 

That company had a tech who came across a unit with a blown fuse. He didn't have one so he put a piece of wire in its place. That night the unit over heated and burned down the building. The tech got 20 years in jail for overriding the safety features. Wasn't the only time I've seen it either. I went to one machine that had half of it melt down and drip on the carpet. it looked like the blob in that old sci fi movie. Didn't take me long to research the service history and find out who cheated the safety circuits. They guy was kicked out of the industry and the company had to pay to have the gear replaced and office fixed.

 

Moral here is - don't mess with that circuitry. There are ways of accomplishing that job but its not something an armature should mess with. You have people in that industry very aware of that problem. They may have intentionally ignored using an expander or squelch circuit because it introduces a major safety issue. If that means the guys on top have to listen to him breath well that's no different then a heart monitor. You know the mans alive. If he became unconscious and the breathing changes you must to be able to hear that and recognize he's in trouble. Again, that kind of communications been around a long time. If there are solutions, check with the manufacturers of that kind of gear and see what solutions they have, not forums loaded with armatures who don't know s**t from shinola when it comes to that particular audio industry.

[WRGKMC]

Just doing a quick search I found one of those units with the built in squelch. OTS SP-100D2 Surface Station https://www.amronintl.com/sp-100d-2-surface-buddy-phone2r-ots-900402-000.html

[ForrestS]

Let me start off by saying I appreciate your concern for my safety when I'm in the water. Good communication is key when it comes to this industry.

 

I think we may have misunderstood each other as far as what I'm looking to increase in volume. I want to squash the breathing and boost the taking so its uniform db. I definitely would not want any type of gate because that could be a problem if the divers microphone was weak.

 

As far as industry specific equipment. This particular area of commercial diving simply uses a loud hailer http://www.standardhorizon.com/indexVS.cfm?cmd=DisplayProducts&ProdCatID=87&encProdID=DCE19568750F42074E5C29E4F34B9611&DivisionID=3&isArchived=0%20rel=

 

If you're saying squelch circuit will act as a gate then I don't think that's what I'm after.

[Phil O'Keefe]

How about just using two compressors - one for each audio source (topside and the diver)?

 

[WRGKMC]

Let me start off by saying I appreciate your concern for my safety when I'm in the water. Good communication is key when it comes to this industry.

 

I think we may have misunderstood each other as far as what I'm looking to increase in volume. I want to squash the breathing and boost the taking so its uniform db. I definitely would not want any type of gate because that could be a problem if the divers microphone was weak.

 

As far as industry specific equipment. This particular area of commercial diving simply uses a loud hailer http://www.standardhorizon.com/index...hived=0%20rel=

 

If you're saying squelch circuit will act as a gate then I don't think that's what I'm after.

 

As I said, A compressor does just the opposite of what you want. It makes the breathing just as loud as the talking. You want to use an Expander which decreases the breathing level and makes the talking louder. The breathing is still heard but at a lower volume level because the noise floor is lowered, not raised. The louder sounds like voice become even louder.

 

A squelch is in that same family except it silences background noise like breathing. Spoken words open the gate and are clearly heard. I would the squelch is tuned to allow the midrange frequencies of the voice to easily open the gate and resist the hissy frequencies of the breathing.

 

I looked at the manual on that unit. I'm not sure how you're getting a compressor to even work. If you're connecting it between the speaker and the units, its not only the wrong impedance but you're risking damaging the unit with the wrong load.

 

That's two strikes against it working. Compressor or expander are not bi direction which is what you need. They are unidirectional only.

You would need something built into the circuity that only affects the signal between the amp and speaker i.e. Squelch as I been saying all along.

 

You wont get a compressor to work on a bi directional intercom line. you might do it on a 4 wire system where the signal going to the diver is separate from the return, but not when you have signals going bi directionally like an intercom.

 

The only thing I can think of is to use the speaker signal, Convert it to line level so you can feed a compressor (or expander as I suggested) then use a second amp to bring the signal back up loud enough to drive a speaker.

 

Signal to speaker inside unit> Convert speaker level to line level> Compressor/expander> Amplifier> Speakers

 

This places the comp/expander on then speaker signal only. It and does not interfere with the signal on the intercom line. Only the top side the speaker will be affected. You could easily add a bypass switch or a switched jack so when these external boxes are disconnected, the unit works normally. The external speaker jack is installed so it breaks the connection to the internal speaker.

 

 

Stick On makes a modules ideal for converting speaker level to line level. You could use some resistors on the extrenal speaker jack to drop the current and skip this unit but this will provide the best fidelity, plus its a solid unit designed for this job. This unit doesnt require power so you could even mount it inside you pager unit if you have space. This unit drops the speaker level to line level so you can feed a compressor at line level.

http://www.mcmelectronics.com/product/555-STP-1

 

Next you need a small compressor/expander. This one is stereo but its small and inexpensive and will run on 12V so long as you limit the current. http://www.fullcompass.com/prod/027125-Rolls-CL151

 

Next you need to reamplify the signal back to speaker level This unit will do the job. You can even run the output of this amp back to your internal speaker plus it runs on 12V. https://www.banggood.com/BlitzWolf-BW-AP1-20W-Mini-12V-Hi-Fi-Audio-Stereo-Power-Digital-Car-Amplifier-FM-MP3-p-1053566.html?rmmds=buy

 

Too bad the solution isn't a bit simpler, but this is the Only way I can see it being done.

 

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