Phase reversal on MIC2200 pre-amp

Hookin up those Audio Boxes without gettin yourself Perplexed.
Post Reply
JJ2013
Voodoo Audiophile
Posts: 140
Joined: Sat Apr 27, 2013 9:16 pm

Phase reversal on MIC2200 pre-amp

Post by JJ2013 » Tue Jun 03, 2014 1:31 pm

Hi y'all Audioheads, Audiophiles and VooDoo Gurus!!

As I was playing around with my Michael Joly Engineering condenser mic, I pushed the phase reversal button in just for kicks and noticed that my presets took on a more basy timbre thereafter! Also, it seems that the ALC on my TS870 behaves somewhat differently too after the phase reversal : ))

NOT all bad actually and I will probably continue fiddling with this a bit, but wondered if anyone else has done this and what their findings may have been?? All this may not be relevant to my situation as my rack, mic, rig etc. are different from yours but just curious about the phase reversal (input signal undergoes a 180 degree phase shift when using this feature).

C'mon, let's hear it :lol:

Cheers!

JJ

BillPaul
Digital Voodoo Guru
Posts: 66
Joined: Wed Jan 19, 2011 11:52 am

Post by BillPaul » Mon Jul 07, 2014 12:36 pm

(I know this question has been languishing for a while, but I only just noticed it. I figured I may as well chime in.)

The phase reversal feature on the MIC2200 basically flips your audio waveform upside down. It's sometimes used for noise cancellation in pure audio applications (audio engineers sometimes set up a second mic near a noise source and set it to the opposite phase of the main mic so that the signal from the "noise mic" cancels out the noise picked up from the main mic.)

However it shouldn't make much of a difference if you're operating in single sideband mode (USB/LSB). Your output RF envelope should look much the same regardless of how it's set, and at least for me, I don't notice much change in the way I sound when listening in the monitor on my TS-950SDX.

On AM mode, it has the effect of swapping your positive and negative peaks, which may be useful if your voice has some asymmetry in it (which most voices do -- mine does). Asymmetry means that you may have higher peaks in one direction compared to the other. You see this in complex audio waveforms like speech, as opposed to a simple waveform like a whistle (which is just a pure sine wave).

Ideally, when operating in AM mode, you'd like those higher peaks to correspond to your positive peaks, since that means you may get more positive modulation without your negative peaks going completely to zero. If you examine your RF envelope on a scope and you see that things are the opposite (i.e. your negative peaks are more pronounced than the positive), you can hit the phase reverse switch to swap things around.

When I do this on AM, at least with my rig and my voice, the resulting oscilloscope display shows higher positive peaks than negative and the audio sounds clearer (I think this is because with the phase the wrong way, the excessive negative peaks cause overmodulation in the negative direction which results in distortion, but I could be wrong).

If you're operating in SSB though, I can't account for the apparent difference in how your audio sounds, because it shouldn't change that much. However, it's possible that the way the MIC2200 works, they're feeding the audio through a separate buffer stage in order to achieve the phase reversal, and maybe that buffer amplifier is changing the characteristics of the audio waveform somehow, aside from just flipping the phase (which really it shouldn't do).

Note that I think Mike WZ5Q is in the middle of moving to a new QTH so it might be a while before he throws his two cents in. :)

-Bill, N1GPT

JJ2013
Voodoo Audiophile
Posts: 140
Joined: Sat Apr 27, 2013 9:16 pm

Post by JJ2013 » Sat Jul 19, 2014 8:44 pm

Hi Bill,

I sure appreciate the answer which was pretty clear and unambiguous enabling even me to understand :wink:

Thanks again and I hope we get to meet on the air some time although I can only do 20/15 and 10 at present.

73 de JJ
NI2M

User avatar
Voodoo Guru
VooDoo Site Admin
Posts: 717
Joined: Wed Feb 23, 2005 8:47 am
Location: Down there on the right...

Post by Voodoo Guru » Tue Aug 19, 2014 12:47 am

Howdy Y'all,
Yes, Still moving the QTH,
WOW what a PITA. Now trying to get the old QTH ready to list.

Terrific information as always Bill.
I might add that the phase reversal is also handy to have in the headphone amplifier for your TX monitor. Reason being is that once the audio chain is set up for correct positive peak polarity, you will want the headphone audio phase to be switchable at the headphones due to skull bone conduction.

Steve, W1QIX stated this:
"When monitoring in headphones at the same time your are speaking on the air, it is vitally important that you be able to change the phase of the headphones. Due to bone conduction, you will always hear your own voice, even when your ears are closed off, while you are speaking. You want the sounds coming from the headphones to be in phase with the sounds your ears are receiving directly from your voice. There is a dramatic difference in the sound you will hear through headphones, monitoring your own voice, when the sound from the headphones is in phase or out of phase with what you hear through bone conduction. Be sure your modulation monitor or monitoring system (if you build your own) has a headphone phase switch!"
http://www.classeradio.com/review.htm

Take Care,
Voodoo Guru
From Deep in the IDD of the Sub-Harmonix Realm

JJ2013
Voodoo Audiophile
Posts: 140
Joined: Sat Apr 27, 2013 9:16 pm

Post by JJ2013 » Thu Aug 21, 2014 7:12 pm

Hi VooDoo Guru!

That headphone piece was great!! Much obliged 8)

Cheers!!

JJ

Post Reply