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Audio Distortion on 6400

DaveM Member ✭✭

I am unable to get clean, undistorted audio on my 6400 running remotely on SmartLink. I have adjusted and re-adjusted all of the audio settings without any success. I am 100% certain that I am not overdriving. In fact, I have duplicated on my 6400 the exact settings and mic that are known to give clean audio on another 6400 remote station - without success.

FWIW, my station works flawlessly on CW and digital modes.

The only difference in operatizing characteristics between the two stations is the internet connection. My station has an "excellent" connection 90 per cent of the time, but the latency is 50-60 ms, never less, and sometimes more which I assume has an impact on audio. The other station with clean audio has latency in the single digits.

When I operate at the fixed station on the LAN (not remote), the audio is very clean.

I might try talking to the ISP to see if any internet adjustments can be made pending comments to this discussion.

Any thoughts or suggestions for improvement?

Dave, N4CQ


  • Ha Gei
    Ha Gei Member ✭✭✭


    the same here. Also, you can find a lot of other stations that have the same problem. Flex seems to be the master of making software worse each update to me. The problem was introduced 2 or 3 updates ago.

    Unfortunately you cannot go back enough, due to authentication changes . We are very dissapointed what happens with these otherwise fine radios. I also own old hardware ( 3000 ) and there the software is flawless and gets improved every now and the by ONE single person with strong will to be perfect and satisfy his users for free.

    Workarounds posted elsewhere:

    Stop DAX usage when using windows standard audio. Maybe use DAX for SSB instead of standard TX path. Use a 3rd Party audio solution to the MIC input .



  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin
    edited February 6

    Most of the time, when we hear about bad TX audio it is related to overdriving the audio.

    Dave didn't mention that he was actually watching the Level Meter which is key.

    When it is related to a SmartLink connection, there are many places Audio can get overdriven. Again, the first place to watch is the Level Meter in SmartSDR. Keep it at -5db and if you do any EQ boosting, you need to reduce the maximum peaks on the Level Meter.

    We could help further if there was more detail on what 'bad' is. So many customers call in and say it is bad, but only because someone said it was 'bad'. Sometimes 'bad' means it isn't flawless perfect but yet, it is certainly communications quality.

    If the problem was in the software, then you would have your entire install base with the same problem as everyone is running the same software and the software does not change between installations of SmartSDR at the same version. We know this when we test Alpha software and all members of the Alpha team report the same symptom.

    So, what can cause bad TX audio on a SmartLink connection?

    • Overdriving the Mic input on the PC - you can us the PC to actually monitor your Mic input - this is a Windows feature
    • Network packet loss - this is very possible especially if the client that SmartSDR is running on is on WiFi. WiFi networks are not the best at VoIP streaming audio. You might hear this on Skype Test Calls.
    • The Router on the user network doesn't handle upstream data very well? It happens
    • MTU values are too high and this results in fragmented packets going to the radio and lots of UDP packets being dropped
    • And, of course, it could be the radio. However, since you mention that it is ok on a local LAN, that likely isn't the issue, at least at this point. This is why focussing on the above would be the first place to start.
    • A recording of the 'bad audio' is hugely helpful. Is there any chance you can do that? What happens if you listen to yourself in Full Duplex? Next time you get a report of 'bad audio', slide off frequency and listen to yourself.

    Remember, the 'bad audio' is just the symptom of the problem. It is not the root cause of what is happening. So, like good hams, we need to do a bit of diagnosis next. And, that is to find out what works and what doesn't. That then will help eliminate parts that can contribute to the symptom.

    For Dave, I opened a support ticket for him.


    BTW, many of us use 3.3.33 all day long on SmartLink with no 'bad' audio

  • Ha Gei
    Ha Gei Member ✭✭✭

    It´s not overdriven, and when i reduce gain, it´s beeing reported as even worse. There is no router , just a pair of WIFI bridges ( Ubi 100Mbit link at superb fieldstrenght. ) . I have all bars green.

    The Audio input , fed into the FTDX100 here locally is perfect, as well as the same mic feeding the 6500 directly also is perfect.

    It sounds harsh, like many random microdropouts. Only at normal USB using the standard sound uplinking. FT8 , used by a friend from the internet into my home net and then over the same link to the 6400 is also flawless. Even rerouting it thro rcforb into the ftdx is perfect. Same when he runs VaraC. I here the same sound from a bunch of remote operated 6xxx on the band. Also HB9RYZ and others have reported that effects . It was all perfect until 3.3.32 . I will give a try using DAX as the upload path, but as i remember this had added delay when used earlier.



  • John KB4DU
    John KB4DU Member ✭✭✭✭

    Dave, have you tried listening to yourself using a remote receiver like on webSDR? May give a better sense of how the audio sounds.

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

    The only issue with TCP/IP is that if you have packet loss you will hear that on a transmitted signal. The bars are for RF Strength and do nothing to tell us about any packet loss of collisions. It is a great alignment tool but that is about it.

    How are you listening to your audio on the FTDX10? Are you listening to your transmitted FlexRadio signal?

    If it was my hardware, I would run iPerf (https://github.com/esnet/iperf) on both ends and actually test the RF link for packet loss. It is possible there are items like mismatched MTU settings resulting in packet fragmentation. One of the things they teach you in Networking school is that it is easy to get a network to communicate. It is hard to make it work at 100%.

    You didn't mention what the audio level meter is doing.

    The next step is to actually listen to yourself. First, do it on the Windows computer https://www.cyberacoustics.com/how-to-get-microphone-playback-windows-10. We want to make sure the Mic isn't part of the problem.

    Next, can you provide an audio recording from either listening to yourself in FDX or via a WebSDR? I still have no idea what it sounds like, other than bad.


  • DaveM
    DaveM Member ✭✭


    Thanks for the feedback and comments. I will attempt to summarize my comments on all of the above comments.

    I have had the distorted audio since I installed the 6400 (v 3.3.33) and began to operate remotely at the turn of 2023. There is no difference running less than 100 watts or 1500 watts. Both digital modes and CW work as expected. I do not have distorted audio when I operate on the LAN using the mic plugged into the back of the radio. I am aware that there are many Flex radios operating perfectly with no problems. KEEP READING TO THE END.

    Over the last week or so, I have had numerous email exchanges with Ken Wells on this issue. He suggested that I was overdriving the radio which may have been somewhat true, but I do not now believe that this is the likely driver of the problem. (BTW, I really do appreciate Ken's expertise and the time that he puts into replies as well as the promptness of his replies. Frankly it would be somewhat difficult to improve on his service in that regard.) So let me explain further on my position.

    I have listened to the output on a recording made by my ham buddy, WB4KSP. It is clearly distorted and muffled. I have also had numerous comments from stateside and DX stations telling me that the audio was distorted and unintelligible. Unfortunately I do not have a recording to share at this time.

    Today, I stumbled into two professional broadcast engineers on 40 meters, and they listened to my transmission and reached a mutual conclusion. They believe that I have RF getting into the transmission thru a separate path that does not exist when operating on the LAN (since on LAN operation there is no distortion.) This hypothesis would eliminate a malfunction of the radio/software and maybe other station components.

    I was not aware of, nor did I consider this possibility, but it does make sense now that I think about it. Both engineers suggested that I run some tests at the station - operating remotely on a separate internet connect and computer/laptop. I can do this since I have separate, redundant Internet suppliers at the station location. (There was a time when I had no internet, now I have two separate connections.)

    I am totally unfamiliar with how to troubleshoot this problem and am hoping that somewhere the issue has come up before. Ferrites of course help the usual RF problems. The only idea that comes to mind is that the ethernet connection to the computer and radio is fairly lengthy and is acting as an "RF Antenna." of sorts. The ethernet cable from the router connects to a switch which feeds multiple items` including the radio, computer, and TGXL.

    Any ideas how to attack this problem would be appreciated. I plan to open a ticket on the problem as suggested by Ken for record purposes. If a ticket is already open, I won't need to do that. Thanks again to all for listening.



  • John KB4DU
    John KB4DU Member ✭✭✭✭

    The idea by the engineer types sounds plausible. One approach mentioned in another thread is to use fiber optic cables which are much more RFI resistant.

  • DaveM
    DaveM Member ✭✭

    I am aware of the advantage of fiber cable, but I would need media converters on every cable where there is a fiber interface.

    My station uses fiber from the ISP service point to the modem due to the long distance from the service point, then I use a media converter to connect a short cable to the ISP modem.

    The common mode ethernet chokes from DXE isan interesting idea - something to look into

    Thanks for the suggestions

    Dave, N4CQ

  • John K3MA
    John K3MA Member ✭✭
    edited March 1

    In my opinion, you need to first confirm if it is RF or not. One potential way to do that easily is to have another Flex user that has a known good remote setup working to use SmartLink on his computer and location to sign in to your remote station and see if his audio also has the same distortion. If it does then you know for sure the problem is at your remote station and not something at your operating location and equipment. It does not rule out your ISP provider but you could verify that in other ways.

    Of course, you would need to provide your SmartLink login to this person so either you need to trust them or change the password afterward.

    Of course, this does not solve the issue but it does provide location-specific information that is useful for more troubleshooting.

  • DaveM
    DaveM Member ✭✭

    Hi John,

    Great comment and I have already done that test. I share another 6400 with a friend in Florida, and we ran that exact test from his location using his setup on my station. The result was the same.

    I am going to make a recording of the audio and get it to the Flex guys and see what they think. I have heard it and it sounds like RF to me.


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