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Setting up an audio chain




 
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WZ8J
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« on: January 28, 2019, 07:42:03 PM »

So I have messed a tiny bit with outboard audio on both a Globe King 500A and a Valiant and have been encouraged by the results.
Shure M68FC mixer feeding Sony 7 band graphic EQ from my college days stereo (think 1980's) feeding the audio to the cathode of the 6C4 in the Valiant and to the first audio in the GK. Mic is a Suzuki SMD 258 picked up in an instrument micing set for 15 bucks new.
disclaimer (I did a cursory search on this site to make sure this hasn't been covered 98 times already and to avoid the ensuing backlash from the collective. If it is already posted I was too lazy to find it)
Just bought a Behringer VX2000 from a friend which sports a limiter, compressor, downward expander and EQ. The goal is to get a new toy to replace the lash-up described above and to get a new toy. Should arive this week  Cool

So what is the correct sequence to follow to set up the new audio processor? i.e, adjusting the limiting, compressing, eq, etc?
Are there starting point values you would recommend for each of these audio tools?
I have a scope and can make use of the web SDR sites to get recordings of transmitted audio.
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KK4YY
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« Reply #1 on: January 28, 2019, 10:05:26 PM »

I have one of those. The correct sequence for set-up begins with reading the manual. Grin

Don

* vx2000.pdf (1544.43 KB - downloaded 30 times.)
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WZ8J
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« Reply #2 on: January 29, 2019, 06:35:45 AM »

You sound like my late father (AC8EL) Don,
"If all else fails, read the directions" Roll Eyes  Cheesy
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N1BCG
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« Reply #3 on: January 29, 2019, 07:29:27 AM »

Like most mic processors, the VX2000 has its audio components set up with the equalization placed after the compression (the popular 528 series does this as well). This is ideal for studio recording and disasterous for transmission processing. Here’s why...

You’ll certainly want to be boosting your “presence” frequencies around 2-4kHz to enhance clarity. This is a form of audio pre-emphasis particularly important to help overcome band noise and narrow receiver roll off. If this is done using an EQ placed after the level controlling stage (compressor / limiter) then your higher vocal frequencies will cause overmodulation and splatter because they are boosted higher than the lower frequencies.

The solution in some microphone processors is to use “inserts” connections on the units to manually re-arrange the order and place the compressor (definitely the limiter) as the last function before the output. With this done, you can cut or boost any frequency to optimize your audio and the compressor/limiter will ensure nothing exceeds max modulation.

Another solution is to add a separate limiter after a microphone processor. This could be one that is designed specifically for audio peak management and bandwidth limiting such as the Inovonics 222, to name one of the more common.

As for the order of adjustment, leave the EQ “flat” then set the compression to provide the amount of gain control you desire (this is wildly subjective) and make sure that whatever performs the limiting function is set to its fastest response time to best handle peaks. Your final output level is adjusted during this process to maintain no more than 100% modulation. Next, adjust the EQ first by gradually boosting the 2-4 kHz range until to reduce the muffled sound you likely have without any EQ.

It’s generally unnecessary to boost any low frequencies, but some ops do and end up with fake sounding audio and muddy lows. This also fights against the presence boost you just established.

Have fun with the new box!
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VE3ELQ
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« Reply #4 on: January 29, 2019, 08:45:00 AM »

Just for info I have a 10 band stereo EQ on order from our favorite Asian country as the price was right. My intent is to make a box for it and see how it plays.  Frequency control points 35HZ, 75HZ, 160HZ, 350HZ, 700HZ, 1000HZ, 1800HZ, 3500HZ, 6500HZ, 12000HZ.   It should be able to tailor my mics and steeply roll off the highs using the last 3 sliders to keep my AM bandwidth respectable.

https://www.ebay.com/itm/10-Band-Stereo-Two-Channel-EQ-Equalizer-Effects-Adjustable-Audio-Tone-Board-/322469044266

73s  Nigel
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KL7OF
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« Reply #5 on: January 29, 2019, 08:55:04 AM »

Just for info I have a 10 band stereo EQ on order from our favorite Asian country as the price was right. My intent is to make a box for it and see how it plays.  Frequency control points 35HZ, 75HZ, 160HZ, 350HZ, 700HZ, 1000HZ, 1800HZ, 3500HZ, 6500HZ, 12000HZ.   It should be able to tailor my mics and steeply roll off the highs using the last 3 sliders to keep my AM bandwidth respectable.

https://www.ebay.com/itm/10-Band-Stereo-Two-Channel-EQ-Equalizer-Effects-Adjustable-Audio-Tone-Board-/322469044266

73s  Nigel
Nigel....This is interesting...Please keep us informed on  how this project works out....Good Luck   Steve KL7OF
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N1BCG
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« Reply #6 on: January 29, 2019, 10:03:06 AM »

For those who have basic stereo compressor/limiters and EQs, here's an arrangement that puts all the channels to good use and mimicks the function of high-end broadcast processing. I used a DBX 166XL and a Yamaha GQ2015 simply because I had them. Other models can easily be used in this configuration:

Microphone PreAmp -> Compressor/Limiter Left -> Equalizer Left -> Compressor/Limiter Right -> Equalizer Right -> Transmitter


1) Compressor/Limiter Left Channel:

Role: Automatic Gain Control (AGC)
Benefit: Maintains consistent modulation for varying input levels due to normal fluctuations in voice level or moving closer or further from the microphone

Since most of these units are designed to operate from either consumer line level (unbalanced RCA or Phone jacks) or professional level (balanced XLR jacks), the audio from the microphone will need to be amplified by a preamp or audio mixing board. With the proper input level, the left channel would be set to automatically regulate the audio levels.  Here are some typical settings:

Threshold: Set for around 12dB of gain reduction with normal speech
Compression Ratio: 2:1 to 4:1
Attack Time: Fast or shortest time
Release Time: This sets the density or aggressiveness of the audio, increasing with faster or shorter time
Limiter/Clipper: If present, set this so that it has minimal effect
Output Level: Set so that the output level is comparable to the level being fed into the compressor


2) Equalizer Left Channel:

Role: Pre-Emphasis Curve
Benefit: Increases intelligibility by boosting audio frequencies that the ear is most sensitive to

Many receivers begin to roll off frequency response above 1 kHz, so to compensate and to sound less "muddy", the "presence frequencies" between 3 and 5 kHz are amplified more than the rest.  The following are approximate settings since equalizers vary in design and band assignments, but the sliders beginning around 1kHz should be set for a smooth increase to achieve the following:

2-4 kHz: 4dB boost
5-6 kHz: 8dB boost
All bands below 1kHz and above 6kHz: Flat or unity gain


3) Compressor/Limiter Right Channel:

Role: Peak Limiter
Benefit: Allows for maximum modulation and prevents peaks from causing splatter or even damaging transmitter or amplifier components

While the first stage of compression helps to smooth out audio levels, the pre-emphasis function of the equalizer further boosts audio frequencies that would cause overmodulation if not kept in check. Average levels have been handled so this stage will address the short-term peaks with these common settings:

Threshold: Set for around 3dB of gain reduction with normal speech
Compression Ratio: Infinity:1 or whatever the highest ratio is
Attack Time: Fast or shortest time
Release Time: Fast or shortest time
Limiter/Clipper: If present, this should be set to do most of the work. See following discussion.
Output Level: This is what sets modulation using and oscilloscope or modulation monitor.

Compressor/Limiters vary greatly in their ability to limit peaks and how this function is measure varies as well. For example, a DXB-166XL features a "Peakstop Limiter" and a single LED. The control would be set on this kind of unit so that the LED flickers with normal speech. A Symetrix 565E has several LEDs that indicate limiting between -12dB and -3dB. The control would be set for -3dB (one LED) with normal speech.


4) Equalizer Right Channel:

Role: Low Pass Filter
Benefit: Limits excessive bandwidth generated from limiting/clipping while passing useful audio frequencies

Many receivers begin to roll off frequency response above 1 kHz, so to compensate and to sound less "muddy", the "presence frequencies" between 3 and 5 kHz are amplified more than the rest.  The following are approximate settings since equalizers vary in design and band assignments, but the sliders beginning around 1kHz should be set for a smooth increase to achieve the following:

All bands below 5kHz: Flat or unity gain
All bands above 5kHz: Minimum gain (sliders all the way down)



* Figure 1.jpg (115.98 KB, 1032x434 - viewed 87 times.)
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KK4YY
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« Reply #7 on: January 29, 2019, 06:05:10 PM »

Clark,

My only change to your scheme would be, on "Equalizer Left Channel", to set all sliders above 6kHz to minimum. This would stop "Compressor/Limiter Right Channel" from responding to sounds above 6kHz that won't be going on-air anyway. Why have an ess at 8kHz cause compression that won't be heard? It pumps the compressor for no reason.

P.S. I'm also using series compression.

Don
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N1BCG
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« Reply #8 on: January 29, 2019, 07:37:22 PM »

My only change to your scheme would be, on "Equalizer Left Channel", to set all sliders above 6kHz to minimum.

Absolutely! There's a lot of merit to that suggestion. In fact, that would also steepen the high frequency rolloff, providing even more precise bandwidth control.
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KK4YY
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« Reply #9 on: January 29, 2019, 08:20:47 PM »

My experience with the Behringer VX-2000 was:

- The mic preamp didn't have enough gain to properly drive the compressor. At first, I though the compressor wasn't working. I used an external mic preamp and all was well. This may have just been my particular VX-2000.

- I bought it used on Ebay. I noticed that one of the op-amps had been replaced. Subsequently, a different op-amp crapped out that I needed to replace myself. This is a fun thing to do - if you like figuring out Chinese puzzles!

- Some of the front panel nomenclature is ambiguous, at best. I needed to read the manual (I hate to say that again) to figure it out.

- The Expander, Tube Emulator, and De-esser were of no value to me. I didn't use them.

- It has a phase reversal button. Awesome!

Clark decribes the AGC/leveling function. If all you do is achieve that with your VX-2000, you're ahead of the game. My rule of thumb is: If it sounds compressed, you're using too much.

Don
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Steve - K4HX
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« Reply #10 on: January 29, 2019, 10:43:16 PM »

It's best to break into an existing QSO, preferably one with many in the group. Then ask for audio reports. Make adjustments while transmitting, with lots of yeah..yeah....test...ahhh...sshhh. Then ask for another round of audio reports. Continue this cycle until everyone signs out. Bonus points if you have a very weak signal as received by all other stations in the QSO.

This is what AM is all about.
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WZ8J
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« Reply #11 on: January 30, 2019, 08:47:22 AM »

It's best to break into an existing QSO, preferably one with many in the group. Then ask for audio reports. Make adjustments while transmitting, with lots of yeah..yeah....test...ahhh...sshhh. Then ask for another round of audio reports. Continue this cycle until everyone signs out. Bonus points if you have a very weak signal as received by all other stations in the QSO.

This is what AM is all about.

This never happens... Roll Eyes Wink

Thanks Clark, Nigel and everyone who replied with helpful detail and some humor too. I'm in Grand Rapids and might not be getting out today with the foot of snow, more on the way and -4 degrees and 30 mph wind.
When I get home if the box has arrived, I will give the suggestions a try, report results and then get into  a round table on low power and ask everyone for an audio report.
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WD8BIL
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« Reply #12 on: January 30, 2019, 11:28:18 AM »

And ifn you're really pissweak, your old buzzards MUST be, at least, 10 minutes long!
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N1BCG
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« Reply #13 on: January 30, 2019, 12:02:04 PM »

There's an interesting EQ trick that enhances important presence frequencies. Instead of fully boosting the 2k-4k range, some ops add a gradual low end roll off beginning around 200Hz. This is particularly effective when being heard on receivers with limited low end response (which are quite a few!)

In some cases this also increases asymmetry by reducing the frequencies that often contain opposite polarity peaks than what is found in the presence frequencies. Even when mics are "phased" correctly, it is usually just for the majority of frequencies.


* LowCut.jpg (97.02 KB, 770x617 - viewed 68 times.)
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K1JJ
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« Reply #14 on: January 30, 2019, 01:34:32 PM »

Continue this cycle until everyone signs out. This is what AM is all about.

 Grin Grin


A classic exchange heard every so often:


JN = Johnny Novice    OT = Old Timer



JN: "Break-break - How's my audio quality?"

OT: "You need to talk longer to tell - but you have no highs and no lows..."

JN: "Is this better?"

 OT: "About the same - but you still need to talk longer."

JN: "Hold on - let me try a different carbon hand mic"  (a minute passes)   "OK, better now?"

OT: "  [sigh]  Yeah,  sure... sounds absolutely fabulous now... just like a broadcash station - don't touch a thing."                                                    
  
JN: " Oh, thanks, OM! - You just made my day!   I gotta go now, 73's's's"



BTW, Clark, very interesting info you posted above about audio chains - and the use of both channels.

T
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KK4YY
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« Reply #15 on: January 30, 2019, 08:35:33 PM »

A while back I set-up and used parallel compression. In my case, I split the audio into two channels:
   Channel 1 had a minor amount EQ'ing and just a little bit of compression (rag-chew audio).
   Channel 2 was EQ'ed to a bandwidth of 300hz - 3khz and had quite a bit of compression (DX audio).

I sent both channels to a mixing console where I could vary the ratio of the two into one mix. The idea was to have the density and punch of DX audio while still maintaining a good dynamic range to prevent listener fatigue. When received at full bandwidth (as with good conditions), it was fairly transparent rag-chew audio. If the receiving station narrowed his bandpass (as with poor conditions), he'd mostly hear the very compressed DX audio. How well did it work? You'd have to ask the guy with the receiver. Grin

Buying rack audio equipment, and experimenting with sound, is addicting. The possibilities are limited by your wallet, and your imagination.


Don
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Steve - K4HX
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« Reply #16 on: January 31, 2019, 09:37:51 PM »

All seriousness aside, below are links to four article worth reading.

http://amfone.net/Amforum/index.php?topic=4780.0

http://amfone.net/Amforum/index.php?topic=7138.0

http://amfone.net/ECSound/K1JJ8.htm

http://amfone.net/ECSound/K1JJ1.htm
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K0OKS
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« Reply #17 on: February 02, 2019, 01:03:19 PM »

I would definitely do a gentle high frequency boost curve. I start around 800Hz or just above. Then ramp up slowly such that the peak is around 2.5KHz. For AM I would have 3 KHz the same as 2.5 KHz.

If you voice is “muddy” or people do NOT naturally tell you you have a beautiful voice then it is worth experimenting with bring DOWN (1-6dB depending) the frequencies around 300-500 Hz, with the most reduction around 400 Hz for most people. This will make you sound much more “professional” and “broadcast.” Seriously, try it. Electrovoice knows this and actually builds a notch filter into some of their mics. Note that if your EQ isn’t granular enough then these setting may not work well, because you really do not want to be pulling down 250Hz unless you like to sound like you are on a 70s telephone.

As others have said, be careful boosting lows. They can muddy the transmissions up, even though they sound good through a monitor. A small boost (1-3 dB max) around 160Hz is probably OK, but test it. A reduction around 60Hz is always good to help reduce inevitable hum.
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« Reply #18 on: February 03, 2019, 03:11:08 PM »

Once the audio is perfected, having a switch to go to NASA audio mode is helpful when qrm shows up. It's even better than a 70s telephone.
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WZ8J
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« Reply #19 on: February 07, 2019, 04:03:16 PM »

I played around and made adjustments using the GK500A with the VX2000 and a Suzuki dynamic mic.
Used the SDR websites to record parts of my QSO's and did some experimenting.
I found that my "esses" were bulging out 20 kc's so used the de-esser and reduced the "breath" frequencies which helped.
Here are the current settings:

EXPANDER: Threshold -10db, Depth - Medium (1:00 o'clock) I use this to keep the background noise down
COMPRESSOR: Hard Ratio-ON, and Threshold - (-20db), Release - MEDIUM, Output (0), Enhancer - (Normal)
EQ: Tuning- (175ish), Warmth (-10db), Presence (+2db), Breath (-8db)
De-Esser: Threshold (-15db), Cut Freq (6k2)

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Steve - K4HX
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« Reply #20 on: February 10, 2019, 11:41:59 AM »

My guess is the the 20kc stuff was distortion since it's doubtful the GK500 mod tranny has much response at those frequencies. You do have to be careful when trying to push more high frequencies through iron that has limited high frequency response.
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