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ABOUT Compressors - Xmit Audio Chain




 
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WBear2GCR
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« on: March 03, 2006, 01:16:13 PM »

About Compressors -

The way that almost all compressors work is somewhat counter-intuitive unless it's been explained first.

Imho, given a choice a "soft knee" peak limiter is preferable to a compressor for Ham xmit audio...

The compressor works by first boosting gain while sitting around, then reducing it when presented with an input signal! So, if the compression ratio is set high, the effect is to turn the mic gain all the way up!! When you talk, it turns the "mic gain" back down in proportion to the input signal's level...

It tries to keep the level constant, and high.

The higher the compression ratio and level the more it tries to keep everything at the same level (also time constants play a role here too...but we can ignore them for now).

IF you use heavy compression, it should in fact keep you from overmodulating - but the resulting audio probably won't be pleasing.

OTOH, a peak limiter does nothing until presented with a signal near a threshold. Once passing that threshold, it reduces gain sharply to keep the output signal from going beyond a proscribed maximum. Usually it will permit ~3dB of output change for an input change (above the threshold) of several 10s of dBs...

In summary:

- Light compression can keep your average modulated levels up and if you move around on the mic, keep the variation in level less.

- Peak Limiting will prevent overmodulation no matter what, but have very little effect otherwise.

Many of the commercial products for pro audio and broadcast audio perform both functions, compression and peak limiting. However not all compressors have peak limiters. Some do and some do not have adjustable thresholds (and other parameters) for the limiter section. Caveat Emptor.

          _-_-WBear2GCR

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David, K3TUE
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« Reply #1 on: May 08, 2006, 08:04:58 PM »

Based on all I have heard and read I anticipate a need for the following in my audio chain:

Microphonium
Phantom Power (for condensor mic potential)
Mixer
Limiter (this seems essential)

And the addition of the following would be nice:

EQ
Compressor

I was looking at the behringer UB-802 Mixer with a Behringer VX-2000 a while back.  The VX-2000 seems to have been replaced by the VX-2496.  But now I see that the Behringer MDX-2600 has 2 channels AND a limiter, which would make it an all-in-one solution for the above list of needs, except it does seem to be missing 48V phantom power).

QUESTIONS:
1) Does anyone see some essential audio-chain component I forgot?
2) Does anyone have any experience with the MDX-2600?
3) Am I just totally off base and should be looking at something else.

I ask all of this because I would like to make sure I get something decent, keep my conponent count low, and make sure I have not missed anything.

Thanks.
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David, K3TUE
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« Reply #2 on: May 09, 2006, 07:20:43 PM »

David,

Is there something that says you have to have a condenser microphone?

Lots of good dynamics out there. Let me know price range and I can make some suggestions.
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David, K3TUE
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« Reply #3 on: May 09, 2006, 07:54:22 PM »

Is there something that says you have to have a condenser microphone?

Lots of good dynamics out there. Let me know price range and I can make some suggestions.


Nope, the point was just to keep my price down and my options open.


I have considered condensor mics based on what I have heard and read (much on eHam) and the number of nice mikes at affordable prices ($200 or less) that are also condensor:

   Marshall MXL-990 Mic
      This seems to be noted on eHam as perhaps one of the best cost:performance condensor mics in this price range
   Behringer B-1
      Behringer is much maligned in the music community, but I am not making music, and many seem to like this, and I have heard quite a few which sound quite nice
   Studio Projects C1 Microphone
      I have heard recording, but none on the air, but it sounds nice to my ears


Of course, I would not ignore any of the following, which I hear come highly recommended, but seem to cost a bit more (around $350):

   Sennheiser MD-421 II
      Many have said they like this, but not as many seem to keep it
   Shure SM-7B
      I think W2DTC uses this, and he has a good sound
   Electro Voice RE-27 N/D
      I have heard so much about the RE-20, and then started reading that the RE-27 N/D, while not a successor to the RE-20, is even more suited amateir AM use


I have a couple of mics that will get me going just fine (I hope):

   Astatic D-104
      Too popular to not be worth trying, and many I have heard sound fine
   Turner 22X
      I just liked the way it looked, but don't have a clue what it sounds like
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David, K3TUE
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« Reply #4 on: May 09, 2006, 08:33:05 PM »

OK David, I should have also asked you what kind of transmitter this is coming together with. The choice of microphone is the EASIEST to avoid its being the weak link in the chain, but past a certain point you might not hear much difference.

SO, do tell what you're going to be running there, OM, over over

(Oh, and since you're a neighbor I can probably arrange some loaners)
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David, K3TUE
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« Reply #5 on: May 09, 2006, 08:56:52 PM »

OK David, I should have also asked you what kind of transmitter this is coming together with. The choice of microphone is the EASIEST to avoid its being the weak link in the chain, but past a certain point you might not hear much difference.

SO, do tell what you're going to be running there, OM, over over

I am on a very slow path (personal life slows things down lately) to getting on 75m with a class-E rig.  I like the idea of a class-E modulated by the class-H circuit Steve, WA1QIX uses.  If a weekend allows, I may get the Globe Scout Deluxe I have on the air to test the antenna system and other pieces out.  But I will be looking at a class-E/class-H as my goal.  I plan on keeping my audio bandwidth under 6 kc most of the time, but would like to be able to open things up to 8-12 kc on rare occasions when the band permits and just to show off, just for fun, not often though.

(Oh, and since you're a neighbor I can probably arrange some loaners)

That is very generous of you.  I'll keep this in mind.  Frank, KB3AHE was generous with his time when I was talking about receivers (Frank, if you see this, I still have that D-104 I promised you, just have not had the time to drop by).  I can use all the help I can get.  Thank You.
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David, K3TUE
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« Reply #6 on: May 10, 2006, 08:46:25 AM »

Having just returned from Hosstraders (New Hampshire) where there was not one but TWO of the MOSFET-based transmitters you are considering, I got a good chance to hear in local monitors what the rigs sound like.

For a few hundred bucks you can get a nice dynamic whose strong points include cutting back any off-axis room noise, ruggedness, and not needing any power supply.

Condenser mics are generally fine, and you can get a couple of them for the same money as a good dynamic. I don't know your views on marketing and value for dollar, but my money has gone to the dynamics.

Most of the condenser models are made in China with common capsules in a variety of housings.  There are reports the quality control varies such that if you get a good one, it will stay good, and if you get a bad one. it may fail early and need warranty satisfaction.

The dynamics that I would consider have been around a long time, as have the manufacturers.
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David, K3TUE
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« Reply #7 on: May 10, 2006, 01:57:04 PM »

Most of the condenser models are made in China [and] reports the quality control varies [...]

I have heard this from many, actually, especially in music board threads.  But I discounted this because of the environment differences between road/studio music duty and ham shack duty.


The dynamics that I would consider have been around a long time, as have the manufacturers.

Would your list include any I listed above:

I hear come highly recommended, but seem to cost a bit more (around $350):

   Sennheiser MD-421 II
      Many have said they like this, but not as many seem to keep it
   Shure SM-7B
      I think W2DTC uses this, and he has a good sound
   Electro Voice RE-27 N/D
      I have heard so much about the RE-20, and then started reading that the RE-27 N/D, while not a successor to the RE-20, is even more suited amateir AM use


And do you have others you would suggest?
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David, K3TUE
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« Reply #8 on: May 10, 2006, 03:11:11 PM »

David,

You'll find a lot of support for the RE-27 for two chief reasons: High magnet/coil output, which means your board doesn't have to work as hard to provide gain, and the response rise around 4-4500 that helps with articulation and sibilant sounds. A secondary reason is that it looks cool.

But the Sennheiser 421-II comes very close to the RE-27 characteristics for about $250 less (street price, and after you include the EV's 309 suspension cage). The downside to this one is that you need a windscreen since the diaphragm is very close to the screen and you easily pop the pees.  I have had three of them, two of the II and one of the originals, and I sold one of them only to go buy something else.

Ken, W2DTC recently bought an RE-27 and discontinued his SM-7, finding the differences so obvious and superior. He bought the '27 after a discussion among several of us running the '27 that took place at Frank's Post-Timonium party.

If your voice is more in the tenor range than the basso-profundo range, you could get by with less expensive vocal dynamic mics, including offerings by Shure, Sennheiser, EV, AKG, Audio-Technica and bunch of others. You've already done a lot of research so I presume you've come across recommendations for those. 

One of the best field mics used at the AM Festival Stations has been an EV RE-50, followed by the RE-16. The low end response can be touched up with EQ if need be, but the excellent windscreens, and the anti-handling noise construction (RE-50) make them really strong contenders if you ever plan any rugged outdoor or party situations where spilt beer, cigar smoke, and other hazards abound.



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ab3al
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« Reply #9 on: September 05, 2007, 10:33:51 PM »

on the subject of microphones/// if your looking into marshals look at the v67  $99 online has an almost perfectly flat response from 20-20  look at the curves of all of marshals mikes this is a good starting point. A mike that colors the input is ok but for me tinkering around with recording one of the wisdomes in the sport is input the signal as flat as possible then use your other tools to distort it, not the mic  I like this mike a lot for recording acoustic guitar and vocals.
Have a nueman or two but they are over rated.  Dynamics  mmmmmm love those re20-27s
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Bacon, WA3WDR
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« Reply #10 on: September 06, 2007, 01:39:55 AM »

Mikes are funny - they are supposed to be accurate, but they generally all sound different.  Some sound good on some voices, and others sound good on other voices.  The thing to do is try a few and see which you prefer for your own voice.

You can look at the response curves, and the detailed directional characteristics at various frequencies, and the proximity effect at various distances - but it really doesn't tell you what you think it does about the mike.  Try the thing, that's how you'll know.

I mean, I tried some old bi-directional ribbon mikes that tested sooo flat... and they sounded so muddy on most voices that I couldn't use them for speech at all... except I recorded one country singer, and nothing sounded right except that type of mike - and he sounded fantastic with that same mike that sounded like booming CRAP with everybody else.  An acoustic piano sounded gorgeous with a boomy bi-directional ribbon mike above it and a super-cheapo cardioid electret condenser mike under it, mixed together.

Some condenser mikes are perfect for cymbals, and useless for anything else.  In a closet-sized room with carpet over softboard walls, a low-cost stage dynamic can be the knock-your-socks-off best choice for voice and acoustic guitar.  There are so many variables that it's magic sometimes.

You can get -some- of the sound from the wrong mike if you use heavy equalization, but the right mike is like magic, it's so much better.  And you'll still want equalization to brighten it and maybe diddle the bass, etc.

Compressor-limiters - for voice, an asymmetrical peak limiter with complex time constant is my favorite single-band choice.  The asymmetry works well with the dynamics of speech, and it's good for AM that way too, and the complex time constant makes it behave like a compressor and a peak limiter.  I wish I knew who made a good one.  I built my own.

Equalizers - the old five band graphic types were about right - a few mods, and it's heaven.  But some CEO found out that they were good, and stopped making them.  The lesson of this is: never let a CEO know that a product is good.  Only talk to them about markets and demographics.

   Bacon, WA3WDR
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« Reply #11 on: September 06, 2007, 02:04:33 PM »

I'm with Bacon on this one. Some of the guyz with the RE 20 & 27s sound great. Others who have switched to them didn't achieve anything over their original mikes.

I too, David, had a 22X and it sounded pretty good with a compressor and 5 band graphic eq. But the switch to the marshall 990 was mind blowing to say the least.

In the end the best advise someone gave me was to try as many as possible until you get the station sounding the way YOU want it to sound. If you wanna sound like Tron or VJB or KBW radio shoot for that. But remember, your station is a representation of You. If you were behind me at a fester talking would I be able to recognize your voice based on what you presented on the air ? The AM mode helps a lot with that but ultimately it's your station..... your sound.
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