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Microphone and transmit audio problems with my Flex 6400

For some reason, I can't seem to get my transmit audio to sound decent. I've tried using the "MIC" connection on the back of the Flex 6400 using an 8 pin foster to 3.5mm" audio plug allowing me to use my Yaesu microphones (MH-31 Hand Mic & MD-100 desk Mic) and I've also used a "HyperX Cloud Stinger" Computer Headset into the microphone input of the Windows Computer I'm using and choosing the "PC" selection for the Microphone.

Regardless of which microphone, or microphone source, I'm using the group of Ham's that I usually talk with, that know my voice and hear me on my other radios, tell me that the audio is nowhere near as good as on my other radios (Ten-Tec, ICOM, and Yaesu). I have the other radios providing transmit audio that is pretty much the same and indistinguishable from one radio to the other but the Flex 6400 stands apart as being the poorest audio quality transmitted.

I love the Flex 6400 and the received audio is great but something has to give with the transmitted audio quality because I know others have great audio with the Flex radios because I have heard too many that sound good so I have to be doing something wrong.

One other comment. I've attempted using a Heil PR-10 Mic package using the XLR to 3.5mm connecter cable yet the audio level from the Heil PR-10 is so low that I can't get enough audio into the radio even maxing out the Microphone level slider and activating the Processor function. Is it possible I have a defective PR-10 or do I need some kind of interface box (equalizer/amplifier) between the PR-10, or any other microphone, and the Flex 6400?

Any thoughts or comments? Which are the best microphones to use with the Flex-6400 using the 3.5mm connector on the rear of the radio?


  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin
    edited November 2021

    I answered this in Facebook for you.

    What does it sound like when you listen to yourself using Full Duplex? I never ever have someone else tell me how they want me to sound to their ears. Doing so allows you to play with the EQ and always downmix first. Next, make sure your Level never ever exceeds -5db (or less if you are boosting in EQ).

    The next surprising part is that radios that 'splatter' sound great since they are now using more radio bandwidth that your Flex which is a very controlled signal. You need to check your HighPass and LowPass mic filters.

    If you watch enough SSB signals on your radio, you will some of the best sounding signals are really dirty and splattering.

    Posting screen shots of your Settings (EQ, Mic Gain, Low Cut and High Cut) filters will have to give you a more detailed answer.

    You also have to ask, is the audio you want for rag chewing or working DX as they are different audio shapping.

    This video might help

  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Hi Gary, Is your mic gain set too high?

    Make sure that your mic gain is such that the peak indicator never goes into the red. It should be adjusted so that the indicator is somewhere between -10 and 0. I try to get mine to peak at somewhere around -5 dB.



    You might also want to take a look at some YouTube videos my Ken Wells, NM9P. He has done a great job of explaining how to use the full duplex feature of Flex radios to set the TX Equalizer.

    The two mics that I use are the FHM-3 (stock hand-mic) and the Yamaha CM-500 headset. I get good audio reports consistently with these mics. I do have the equalization set differently for each mic, and it makes a big difference. Note that you do need an adapter for the CM-500. I found it very easy to build, but not everyone wants to melt solder...

  • John KB4DU
    John KB4DU Member ✭✭✭✭

    Can you describe how the Flex sounds to the others? I use settings very similar to Kens and only get good unsolicited audio reports.

    Maybe start with everything set to a flat baseline, all to eq set to zero, no boost or cut, processing set to normal, bandwidth set to 2700 (I use 300-3000). Then record yourself talking and determine what needs to change. If changing eq, always cut before boost, especially important on the flex because the mic level meter is before the eq, so boosted frequencies can overdrive the audio chain.

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