The AM Forum
March 28, 2024, 05:10:33 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Where does the "gate" go?  (Read 9635 times)
0 Members and 1 Guest are viewing this topic.
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 8308



WWW
« on: May 03, 2011, 06:55:25 PM »

It was covered in another topic (http://amfone.net/Amforum/index.php?topic=19484.0) that this arrangement should be fine:

MIC -> MIC amp -> phase rotator -> EQ -> Compressor (and possibly a peak limiter)-> modulator.

I got hold of an old Omni Craft GT-4. This is a 1U unit with 4 gates. The gates can be keyed, but more importantly they are activated by audio input. When the audio input reaches a certain level, the gate magically opens and lets the signal through. It looks like the level threshold necessary to activate the gate is set with one knob and another knob determines the release time.

Where would this thing go in the audio chain? Up front after the mic amp?







* GT4.jpg (54.97 KB, 800x561 - viewed 712 times.)
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
W7TFO
WTF-OVER in 7 land Dennis
Contributing
Member
*
Offline Offline

Posts: 2521


IN A TRIODE NO ONE CAN HEAR YOUR SCREEN


WWW
« Reply #1 on: May 04, 2011, 12:52:11 AM »

Noise gates are to help with noise, acoustic or electronic.  Do you have a noise problem?  Maybe better to remedy rather than mask it...

I'd locate it (if you use it) just after the noisiest place in the chain, providing the impedance and levels agree with it.

73DG
Logged

Just pacing the Farady cage...
Gito
Guest
« Reply #2 on: May 04, 2011, 04:30:43 AM »

Hi

 It depends how we use a Mike, a mike doesn't only amplify Our voice,but also amplify,the noise that all are around us,maybe the sound of a fan,or the sound of rain outside,all thought it's not as loud as our voice but it will be amplified to.

In the other hand a compressor will make a  weak sound loud/amplified and also compress /limiting the loudest sound/leveling it ,so the dynamic audio volume is small.


So when we open the mike ,and we don't talk into it ,the compressor wiill amplify the sound/noise around us to a high level ,and injected  to the modulator amplifier .

As we know ,our sound/speech is much louder then the noise around us,so we set the noise gate (place it before the compressor) till the gate will not pass the noise around us.it only open when we talk into the mike.

Is the noise around Us amplified ?yes,but since our sound/speech is much louder than it,it will mask the noise.

And when open the mike and we don't speak ,the modulator is "noise free",since there's no noise to amplify.


Gito.N


Logged
W2VW
Contributing
Member
*
Offline Offline

Posts: 3489


WWW
« Reply #3 on: May 04, 2011, 05:51:11 AM »

Noise gates are annoying when used on AM IMHO.

If I were to use one it would be installed soon after the mic.

Mic - pre - gate.....
Logged
flintstone mop
Contributing
Member
*
Offline Offline

Posts: 5055


« Reply #4 on: May 04, 2011, 06:30:33 AM »

From an expired listing on eBay it is a 4-channel gate. 4 separate channels that will operate and cut off noise as Gito explains.
Some audio forums found them to be annoying. Mainly used to gate a low impedance source into a high impedance device.
I thought I read that the attack and release times where pre-set.
Logged

Fred KC4MOP
K1JJ
Contributing
Member
*
Offline Offline

Posts: 8893


"Let's go kayaking, Tommy!" - Yaz


« Reply #5 on: May 04, 2011, 09:52:30 AM »

First SSB, then AM comments -


SSB Use:

Audio gates make great tools on SSB. Many of us have blower noise. A gate set properly will mask it - and make it sound like a VOX.  The downside is other stations will sometimes start talking while we still have the PTT keyed, thinking we really are on VOX.  

I use a gate very effectively here on ssb.  Though there is a limit to the level of noise being masked. First of all, without a noise gate, we need to TRANSMIT a signal containing at LEAST a 40db signal to noise ratio on ssb or it may sound like a machine shop in the background. A 30db S/N or less just begins to grate on listeners.  20db S/N is very distracting.  10db S/N is a joke. The S/N is easily seen by watching the S-meter of a calibrated receiver when keyed with no audio and then talking at full power.

I've found that starting with a S/N of no worse than about 28db can be masked well on ssb - and tailor it to about 50db S/N using the gate settings.  The problem with starting with LESS than about 28db S/N room noise is we get inter-mod with the voice. Have you ever heard a guy talking with blower noise mixing with his voice? Strange sounding, indeed.


AM Use:

Do not use an aggressive noise gate on AM if possible. As the Tron always says, "It sounds unnerving".  Work extremely hard to eliminate the background noise using standard acoustical procedures, or simply move the blower outside the room or far away.  However, when running a big AM mawl, a certain amount of blower noise in the background can sound cool. It is the sound of power, but be sure it is low enuff not to cause voice mixing intermod.

Room ambience is always desireable on AM and part of the experience, as long as it's not too loud. Background TV's, XYL yelling, etc, is not a good thang... a quiet background is highly desirable. Grin  


* In most cases, close-talking the mike can help improve S/N dramatically.  Using a pop filter, almost touching the lips to the filter and using minimum audio processing (minimum compression) can usually solve background noise problems.

T
Logged

Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
Gito
Guest
« Reply #6 on: May 04, 2011, 09:58:21 AM »

Hi

I agree Mike ----preamp----gates ----compressor --amplifier.

Like I wrote before "place it(noise gate) before the compressor".
and it depends where We used it in quit room,noisy room,or in a train station.

It depends on the threshold setting of the noise gate.

Even broadcast station used  noise gates,because the audio sources{PC,Tapes .CD ....) has it's own noise.since They also used compressors ,they must also used noise gates.

The point is setting the threshold control of the noise gates.
A good compressor always had a noise gate and it's threshold control ,input gain,compressor and it's Threshold control  ,output gain ...


Gito.N

Logged
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 8308



WWW
« Reply #7 on: May 04, 2011, 11:16:02 PM »

Thanks for the replies, i knew i'd get some good advice. I'll put it in the rack then and see how it wants to be connected. I can also modify it to bypass for AM if I have to. It's real open and easy to work on.

The noise problem here is mechanical. The electronic noises hum and hiss seems to be about 50-60dB down, more noise comes from shuffling papers trying to keep track of who's next.

In the worst offender unfortunately the most powerful AM transmitter where the blowers can't be reasonably relocated outside (what about high humidity +3500V?).

The blower noise from it is not any louder than the HVAC unit in the corner, that is a noisy piece of equipment, sounds like an old pickup truck going down a dirt road. It makes very wide band noises from the squirrel cage intake all the way down to motor hum and harmonics. I've run a few screws into the HVAC unit to stop rattling. Maybe an acoustic panel like a cubicle wall would help, but the intake is well-heard at the operating position. It's a 5-ton air handler.

When I use the speech compressor, it picks up a lot of room noise from the HVAC and the transmitter,  Looks like $20 well spent on the gate.

If I speak close to the mike the level is fine but I need a pop filter no matter how I try to speak. Isee them, a fabric disc of some kind. I've been using no compressor and speaking 10" from the mike loudly and watching the mod scope. I don't like talking so loud though.

Thanks,
PJ
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
Gito
Guest
« Reply #8 on: May 05, 2011, 07:17:11 AM »

Hi

 Reading from the manual Symetrix 425(compressor)  manual book.

It has an expander and followed by a compressor.
What is an expander?  it is a downward expansion,when the signal drops below the threshold control,the expander reduces the gain by it expansion ratio.a 10 db output change ,result a 5 db change in the input signal ,if the expansion ratio is 1:2

When setting the ratio  high it becomes A Gate ,and act like switch when the signal falls below threshold

Using the expander {gate} and compressor together


 These are times when me might to expand and compress simultancously.........
How about a track that has too much dynamic range needs to be squashed to fit into space available in your mix? after squashing,you notice a lot of room noise.amp noise etc. when the track is not active.425 is to the rescue,simply adjust the expander threshold to cause gain reduction during the quit parts of the track and You made these ugly noises disappear.

 Another application for expanding an compressing is Voice processing.
Close mik'ed voices tend to be a little unnatural,things that we don't hear at conventional distance are heard quite well by the announce microphone a bit of expansion will help to reduce lip -smacking noise and some compression will help even out levels and generally tighten up the sound.

An expander with a high  expansion ratio becomes a Gate (noise gate)

Using the expander .

You can used the expander to reduce body noises by an announce microphone.or to reduce amp noise from a noisy  guitar amp.or how about reducing ,the amount of room noise in a guitar track that was recorded in a little too loosely in a room that was too noisy ......how about using the expander  to tend an announce mic that needs  to be left on,but you don't really want picking up every whisper in its vicinity

....adjust the threshold control....

From the symetrix manual.



Gito.N
Logged
W3GMS
Contributing
Member
*
Offline Offline

Posts: 3063



« Reply #9 on: May 05, 2011, 08:33:42 AM »

First SSB, then AM comments -


SSB Use:

Audio gates make great tools on SSB. Many of us have blower noise. A gate set properly will mask it - and make it sound like a VOX.  The downside is other stations will sometimes start talking while we still have the PTT keyed, thinking we really are on VOX.  

I use a gate very effectively here on ssb.  Though there is a limit to the level of noise being masked. First of all, without a noise gate, we need at LEAST a 40db signal to noise ratio on ssb or it may sound like a machine shop in the background. A 30db S/N or less just begins to grate on listeners.  20db S/N is very distracting.  10db S/N is a joke. The S/N is easily seen by watching the S-meter of a calibrated receiver when keyed with no audio and then talking at full power.

I've found that starting with a S/N of no more than about 28db can be masked well on ssb - and tailor it to about 50db S/N using the gate settings.  The problem with starting with LESS than about 28db S/N room noise is we get inter-mod with the voice. Have you ever heard a guy talking with blower noise mixing with his voice? Strange sounding, indeed.


AM Use:

Do not use an aggressive noise gate on AM if possible. As the Tron always says, "It sounds unnerving".  Work extremely hard to eliminate the background noise using standard acoustical procedures, or simply move the blower outside the room or far away.  However, when running a big AM mawl, a certain amount of blower noise in the background can sound cool. It is the sound of power, but be sure it is low enuff not to cause voice mixing intermod.

Room ambience is always desireable on AM and part of the experience, as long as it's not too loud. Background TV's, XYL yelling, etc, is not a good thang... a quiet background is highly desirable. Grin  


* In most cases, close-talking the mike can help improve S/N dramatically.  Using a pop filter, almost touching the lips to the filter and using minimum audio processing (minimum compression) can usually solve background noise problems.

T


Right on Tom!  I have a noise gate in my Symetrics 528E and I really dislike the sound when its on while operating AM.  My background noise is not very high and as Tom has mentioned it add's a bit of "ambiance" to the signal.   If your background noise is somewhat high, I also prefer to turn down the gain on the console and get a bit closer to the mic.  If your using a dynamic be cautious about the extra bass boost with some dynamics when close talking them.  Thats when a good EQ of a mic low end roll off switch comes in handy.  Nothing worse than a PW signal with to much bass!  If you have plenty of fire in the wire thats another story as long as the audio chain can handle the low end.   

Then again on SSB, there is nothing worse than a 10 DB over 9 worth of blower noise between words! 

Joe, W3GMS       
Logged

Simplicity is the Elegance of Design---W3GMS
Gito
Guest
« Reply #10 on: May 05, 2011, 08:59:32 PM »

HI

Only one question ,

the symetrix is only one example, but all of the compressors I know and I used ,like Behringer ,DBX and a  lot of other compressor has an Expander /gate build in.

Why are these "profesional" compander/compressor have an Expander /gate build in.?


Gito.N





Logged
W2VW
Contributing
Member
*
Offline Offline

Posts: 3489


WWW
« Reply #11 on: May 06, 2011, 07:34:19 AM »

For the same reason some cars had vinyl tops.
Logged
Gito
Guest
« Reply #12 on: May 07, 2011, 04:07:48 AM »

hi

what happened when using a compressor without an expander/gate

Fig 21 an  input audio signal with a noise (ambient noise)below the quietest section(blue} the (the red band)

Fig 23A the output audio signal after compression

It is interesting to note that by comparing the input and output waveforms for the compressed mode Th Quietest section  of the input signal  have been effectively raised in level,where as the loudest section have been effectively decreased in level.
the overall effect is that is both ends of the dynamic range have been pushed towards the middle.

The quietest section has been Effectively raised in level including the level of the noise.

Figure 23 B What happened when we open our mike ,there are a high level noise (the ambient noise)(yellow band)  (comparing to the level of the audio).

Halo...SSSSS(high level noise) ...Halo  ..sSSSSSS (just an example}

In the bottom Picture we used a expander/gate to "stop" the noise before it  got. into the compressor.

Gates/expander  are used when we used a compressor
If we don't used a compressor and we are happy with the noise around us of course we don't need a expander/gate.

And if we are happy with the dynamic range of our audio we don't need a compressor.

But if we want a relatively constant level output ( leveling) like picture 23 A ,then we used a expander/gate (to " kill" the ambient noise ) followed by compressor

Gito.N





* IMG_1970.jpg (513.35 KB, 2048x1536 - viewed 458 times.)
Logged
W2VW
Contributing
Member
*
Offline Offline

Posts: 3489


WWW
« Reply #13 on: May 08, 2011, 11:33:04 AM »

A properly set compressor can provide a worthwhile increase in SNR without producing audible distortion.

A gate on a full quieting AM signal will provide little or no increase in SNR. Additionaly it will produce annoying audio artifacts.

Try it.
Logged
Gito
Guest
« Reply #14 on: May 08, 2011, 08:18:24 PM »

Hi

Yes what You wrote is correct.A properly set Compressor increase SNR ......

 I 've used Gates and compressors in life talks/show with 2 or 3 Mike open all the time.in FM radio broadcast studio. And at least to my opinion it works good,

Like You wrote .it works if we set it properly.


Gito.N




Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone © 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.083 seconds with 18 queries.