Microphone audio level

  • 2
  • Question
  • Updated 4 years ago
I use a PR781 microphone connected to the balanced input of my 6500. After installing 1.2 I had to increase my microphone audio level to 65. This is in addition to using the +20 db boost. What I'm wondering is if I wouldn't be better off using a Mic preamp external to the 6500. I've seen where others are doing so and thought I would solicit recommendations or what people are using.
Photo of Jon - KF2E

Jon - KF2E

  • 623 Posts
  • 180 Reply Likes

Posted 4 years ago

  • 2
Photo of Michael - N5TGL

Michael - N5TGL

  • 307 Posts
  • 101 Reply Likes
I think if you are running mic gain at 65 you are fine.  With my RE320, I have the +20db and mic gain at 100 and I'm still -10 down so I definitely could benefit from a preamp.
Photo of Tim - W4TME

Tim - W4TME, Customer Experience Manager

  • 9052 Posts
  • 3435 Reply Likes
It may be better to use a mic preamp from a signal to noise ratio standpoint (assuming of course that the mic pre isn't imparting additional noise into the input), but as Michael says, definitely not necessary in your case.  Setting the mic gain @ 65 with the +20 dB boost is a very acceptable configuration.  

I am a bit biased in this regard since I have "history" with audio sound reinforcement and recording.  I prefer to have all of the input gain needed to drive the radio at the analog input and not make up for it in the DSP stages of the radio.  There is no appreciable difference from this approach and using the DSP gain in the radio, just my preference.  Call me "old school.  I prefer the sound coloring of a tube based mic preamp.
Photo of k0eoo

k0eoo

  • 577 Posts
  • 78 Reply Likes
Jon, I have the 781 and had to increase the levels and add the +20 as well, but my audio reports are great and I sound better than ever in the monitor mode....   End result, I think its OK....  I tested the PROC mode last night with a group of locals on 6M AM.  They were impressed at how great my audio sounded with the new software and how loud it got with in the DX and DX+ modes, with NO distortion....  Dennis, k0eoo
Photo of Dale KB5VE

Dale KB5VE

  • 410 Posts
  • 56 Reply Likes
I am running the pr40 on bal input and I am having to run about 68 on the mic with 20 db on. I would prefer to run without the boost as I could with 1.1.3. The only real problem I had was the downward expanded was on after the download and I did not know why I was clipping for a while. Most say my audio was as good as before but the monitor does not sound as good to me.
Photo of Dale KB5VE

Dale KB5VE

  • 410 Posts
  • 56 Reply Likes
Ok so it is in a different place than 1.1.3?

Really miss the gain in the mic circuit so I did not have to run boost. I have no desire to run external audio gear. Jury out on new processor. Using the 1.1.3 on another drive to get comparisons. Dx appears to be best for punch and sound. Keeping a open mind.
Photo of Tim - W4TME

Tim - W4TME, Customer Experience Manager

  • 9052 Posts
  • 3435 Reply Likes
Personally I am finding that the PROC DX setting is "full bodied" and works well with my voice characteristics.  However, YMMV
Photo of Tim - W4TME

Tim - W4TME, Customer Experience Manager

  • 9052 Posts
  • 3435 Reply Likes
Dale - I just did a test with a PR40 directly connected and my settings are +20 dB Boost with an input gain set for 73; essentially your settings.  I always run the DEXP at 70.  Also I would't be too concerned about having to run the +20 dB boost (mic preamp) with any directly connected mic.  
Photo of Charles - K5UA

Charles - K5UA

  • 310 Posts
  • 86 Reply Likes
Tim, i run a Symetrix 528E pre-amp at mic level into the 6500's balanced input, but i need the +20dB and the mic level set at 66 to achieve decent output. Reading between the lines of your post, I'm wondering if I should drive the 6500 at line level with the +20dB turned off and a much lower mic gain setting on the 6500? That would satisfy having the sufficient mic level at the analog input. My question is.......how much higher is line level than mic level? Will I be exceeding the maximum analog input level by driving at line level?
Photo of Dale KB5VE

Dale KB5VE

  • 410 Posts
  • 56 Reply Likes
Yes with powersdr I always got the best sound with the dx setting. I will just play with it for a while.
Photo of Tim - W4TME

Tim - W4TME, Customer Experience Manager

  • 9052 Posts
  • 3435 Reply Likes
Charles - There are many ways to setup your audio.  The bottom line is if it sounds good to you, then get on the air and make QSOs.  If you want to demon tweak things, then it is all about maximizing the signal to noise ratio (SNR) of your input signal.  In the most simplest terms, you want to feed the radio with the highest SNR signal and not do configure anything in SmartSDR to mess that up.  What you describe is feeding the radio with a low gain input signal and then using the DSP gain in SmartSDR to bring it up to the max level.  I do the same thing too, but I am feeding the 6000 with a higher input gain level so that I do not have to use as much DSP gain in SmartSDR to achieve a 0 dB input signal on voice peaks.


Here is what I do.  I'll describe the physical / electrical connections first.  I have a Studio Projects VTB1 mic preamp (no compression, no EQ) that has a line level balanced output (XLR) that I feed into the XLR connector on the back of my  my 6700.  In SmartSDR, I select the LINE input.  Electrically the BAL and LINE are exactly the same, the only difference is the physical connector  (XLR vs. 1/4" TRS) and in the software, you can not enable the +20 dB mic preamp.  The impedance of the LINE and BAL inputs are exactly the same.

Microphones are low output gain devices so when directly connecting any mic, you should (must) be using the +20 dB boost (really boost is a bit of a misnomer, as it really is the microphone preamp in the radio).  SmartSDR and the 6000 have sufficient gain at different signal path stages to fully modulate the radio with a relatively low output device like a microphone, but not excessive gain so that you can overshoot the ALC and overdrive (clip) the input.

When connecting outboard equipment, you have a lot more gain from the balanced output to drive the radio to full modulation without ever having to enabled the radio's microphone preamp (+20 dB boost - see how I switched the terms on ya :-) ).

You have to visualize the entire audio input signal path and identify the different stages where you can add/subtract gain - known as signal chain gain management.  This includes the outboard hardware and the features in SmartSDR.  For best SNR you want to add just about all of your gain at the first input stage, because you have the least amount of noise at this point in the signal path.  Adding gain at later stages amplifies both the signal and the noise that comes from components in the signal path.

So let's discuss how I setup my TX signal chain.  I have my mic (PR40, SM58 or a variety of condensers) connected to the VTB1 with the proper input impedance set for the particular mic I am using (usually 200 ohms).

The VTB1 has only two gain amplification stages; the mic input and the final output.Your Symetrix 528E has multiple stages with different places to set the gain, the compressor, de-esser, parametric EQ, so you have to be a little more careful in gain management as you have more opportunities to overdrive a particular stage, but a more powerful voice processor to better tailor your audio too. 

I set the mic preamp input gain do that I am peaking at 0 dB most of the time.  The VTB1 has an output gain control that I set at to that the output peaks just sometimes at 0 dB, so I am cutting back just a little of the final output gain before I feed it to the 6700 XLR input.  This ensures that I have a little headroom in the first audio stage.  Be very careful setting the input gain at this stage.  If you overdrive or clip the audio at this point and create noise in the signal input, that noise will get amplified in all subsequent signal path stages where gain can be amplified decreasing your SNR.  Where you are most likely to clip is with percussive voice syllables; speaking words that begin with W and T for example.

Now I have a nice clean, high SNR signal which is close but not 0 dB in strength that I am feeding into the radio.  at this input signal level I do not need the 6000's mic preamp (+20 dB boost). A little more on why my input signal is not completely 0 dB in a second.

Now my VTB1 is only a mic preamp, not a voice processor like the Symetrix 528E (nice peace of gear), so I have to use the EQ in SmartSDR.  The EQ is a DSP gain stage in the TX signal path, so I set the EQ without paying any attention to the input signal level get it sounding good for my voice and the mic I am using.  If you are using the parametric EQ in the 528E and it is set right, you should not need to use the 10-band EQ in SmartSDR.

Same goes for the Downward Expander (DEXP), it can add a little gain when the gate opens fully.  I use the DEXP (everyone should as it increases the apparent dynamic range of your input signal) and set the thresholds so that background noise is attenuated.  On my system that value is around 65, as I have a fairly quiet shack.

At this point I have the PROC turned on and set to DX (my preference after listing to the different settings on a 2nd RX).  The PROC doesn't affect the input gain so changing PROC from off to DX+ should not show any appreciable change in your Level meter.

At this point all of the SmartSDR signal path stages are set so now I need to set the mic gain in SmartSDR (another DSP gain stage) so that it NEVER peaks greater than 0 dB, but gets as close as possible.  In SmartSDR if the input signal ever clips (the peak indicator turns red) that will impart distortion in your transmitted signal.  You need to be  peaking between -5 and -1 dB.  Don't break this rule or all your efforts in gain management have been thrown out the window.

In my radio, the mic gain is set at 8 to achieve peaking between -5 and -1 dB.  

So a vast majority of my input signal gain comes from the VTB1 and I do not have to crank up the DSP gain stages in SmartSDR to compensate.  In this manner I have done what I can to maximize the SNR of the input signal being fed into the radio.  And hopefully that clean input signal results in unsolicited "nice audio" comments when I am in QSO.

(Edited)
Photo of Dale KB5VE

Dale KB5VE

  • 410 Posts
  • 56 Reply Likes
Thank you Tim this is the best explanation of setting the audio on the 6000 series I have seen. I can set powersdr in my sleep but you hit on a key detail of SNR on the input. That explains some of the artifacts that are in some peoples audio. I have avoided external eq's but I might just get a preamp. I use to use a tube preamp and it gave a rich sound. Thank you for some very usefull infromation and Charles thank you for exploring deeper.
Photo of Tim - W4TME

Tim - W4TME, Customer Experience Manager

  • 9052 Posts
  • 3435 Reply Likes
I am glad you found the explanation useful.  The VTB1 has a plate starved 12AX7 in it and you can blend it into the audio.  For less than $200 is is not a bad mic preamp.  Here is a review
(Edited)